Low Tunnel Materials for Protection and Phenological Acceleration of Figs

Progress report for FNE21-973

Project Type: Farmer
Funds awarded in 2021: $3,420.00
Projected End Date: 03/31/2023
Grant Recipient: Finger Lakes Grape Program/Annelise Farms
Region: Northeast
State: New York
Project Leader:
Don Caldwell
Finger Lakes Grape Program/Annelise Farms
Expand All

Project Information

Project Objectives:

This project seeks to find a combination of protection materials in a low tunnel system that will allow figs to both survive winters in the northeast, and accelerate the ripening of figs for increased production.

  1. Winter fig survival through protection materials in low tunnel system.
    1. Temperature data: Within/without low tunnel. Inside 1st/2nd
    2. Phenology data: How many shoots emerged from the buds left after pruning and protecting over the winter.
  2. Accelerating fig ripening with the same materials used in low tunnel system.
    1. Temperature data: How much hotter/cooler depending on combination.
    2. Phenology data: When did bud break occur? When did the first fig form? When did the first fig ripen? How many figs per tree, per treatment?
    3. Pruning weights. Did the phenological boost result in increased growth?

If a combination of materials can be found that protects figs, and accelerates their ripening for increased productivity, farmers will have a system capable of being applied to other semi-hardy perennial crops. Figs, and many of these other crops, require few chemical inputs and outside of low tunnel setup, little labor.


Figs are a semi-hardy woody perennial that suffers significant damage when the temperature falls somewhere under 20 degree Fahrenheit. The second impediment to growing figs in the northeast is their need for a long season. While short season varieties exist that reliably ripen in zone 6, many of the longer season cultivars are regarded as superior. Figs also ripen sequentially, so the quicker the first fruit ripens, the longer the harvest season will be, and the more the trees will yield overall. Figs are a fruit high in nutritional value and require few, if any, chemical inputs to grow well. If a method reliably protecting, and accelerating their ripening, were developed, figs could go from a niche curiosity to a dependable niche tree fruit crop for small scale sustainably minded farms.  Such a protection and ripening scheme could also then be applied to similar semi-hardy perennials such as pomegranates, pistachios, black mulberries, che, and loquats.

               The creation of a farm scale protection and ripening scheme for figs would decrease my reliance on a high tunnel to protect the potted figs. In years past, this high tunnel was heated, representing a significant energy and economic sink. If the protection scheme were adopted by area farmers, they could potentially decrease their reliance on crop systems that are seeing increased pressure from herbicide resistant weeds, insecticide resistant pests, and fungicide resistant mildews. Less chemical inputs in the field mean less in our foods and drinking waters. To find a combination of protection and ripening materials I will use a low tunnel system. These systems are economical and have been shown to provide enough protection to reliably grow winter hardy vegetables. The study of the materials used for these systems has been limited, do not often use a second, interior hoop, and have rarely been studied with a woody perennial in mind. A combination of greenhouse poly plastic, row cover, and mylar film will be used in low tunnels with either a single or double hoop system. Temperature data will be recorded to differentiate the materials used in the low tunnel system, and the outside temperature. Phenology, including timing of bud break, number of shoots emerged versus buds left from pruning, first fig forming, first fig ripening, and total figs ripened by tree, will be recorded in the growing season. This will tell us how well the protection scheme worked, and if it accelerated phenology, ripening, and total yield.

               Once the hoops are in place, and techniques related to the setup of the low tunnel system are learned, farmers will find that overall, labor costs are acceptable. Of the few successful fig farmers in the northeast, Threefold Farm, is able to sell their figs at $1 apiece (Clymer, 2018). Depending on the variety this could mean upwards of $10 per pound. Aside from the fig mite, native to areas of California and other Mediterranean climates, and rust, a fungus prevalent in very warm and wet areas like Florida, figs suffers from few pests. Some minimum of weeds control will be needed, but overall figs need few chemical inputs. Some back of the napkin economics suggest a 533% increase in fig fruit production if trees can emerge winter unscathed and ripen every fig they set (Caldwell, Google Sheet). This could mean $1872 difference per 12 tree row. Farmers may find that figs can be profitable, and very sustainable, if the proposed protection scheme is found successful and duplicable.

Description of farm operation:

Annelise Farms received its nursery grower’s license in March of 2019. I grow figs, pomegranate, and mulberries from cuttings that I then sell as plants to the public through word of mouth and at local farmers markets. I’ve expanded into limited sales of fresh figs to local restaurants, and bakeries. This summer I rented a several fig trees for ambiance and seating demarcation in a restaurant parking lot. I use space in a hoophouse for the cuttings and potted fig trees, otherwise the three (soon to be four) fig tunnels at two locations are my operation.


Click linked name(s) to expand/collapse or show everyone's info
  • Judson Reid - Technical Advisor


Materials and methods:

Research Plan:

Low tunnels will be setup on rented land at two locations: Lake Drum Orchard, 79 Stark Street, Waterloo, NY, and Anthony Road Wine Company, 1020 Anthony Road, Penn Yan.

The low tunnel setup will consist of 10’ long electrical conduit pipes bent to make hoops that are three feet wide, and about 42” tall. The trees will be spaced eight feet apart, in a 100 foot long row (so 12 trees per row). There will be three tunnel rows at one location (site A), and one tunnel row at a second location (site B). All four tunnels will have interior hoops made from 9 gauge soft vineyard wire that are four feet in circumference (one foot wide). All four tunnels will be covered with 6 millimeter thick greenhouse plastic on the exterior hoops. The interior hoops will be covered with different material combinations that will serve as the treatments for the study. As seen in Table 1, tunnel 3 will serve as the control. In the spring, when the threat of sub 20F temperatures abates, all materials will be removed from tunnel 3. Tunnels 1, 2, and 4 will serve as the separate treatments and will keep their materials in place until growth begins to touch the material. So first the interior material will be removed, then the exterior as growth continues.

Table 1: Tunnel Treatments and Locations

Tunnel Name

Exterior Material

Interior Material



Tunnel 1

6 mil poly

1.5oz row cover

Site A

Leave materials until growth touches top.

Tunnel 2

6 mil poly

6 mil mylar

Site A

Leave materials until growth touches top.

Tunnel 3

6 mil poly

2.5mil overwintering poly

Site A

Control. Remove materials after threat of sub 20F temperatures abates.

Tunnel 4

6 mil poly

1.5 row cover/2.5 mil overwinter poly

Site B

Leave materials until growth touches top.


All figs will be trained in a cordon-cane or cordon-spur manner. This requires, and allows, pruning and tying in the fall to fit under the protection scheme of hoops and plastic. Being low and fairly wide creates a large ground footprint under protection. The theory is that ground heat, and not the R-value of the protection materials, is the most important factor in moderating temperature extremes. My familiarity with cordon pruning and growing systems through grapevine production will make phenological tracking easy and reliable.

Three out of four of these tunnels are already planted with fig trees. Six trees were planted in 2018, the other 30 were planted in 2019. This will allow data to be collected regarding fruit production immediately, as 36 out of 48 total trees will be of mature bearing age. Twelve trees will be planted in spring 2021, using the same spacing and will be protected, grown, and trained in the same manner as the older trees. I hope to plant six of the trees to the same variety, and the other six to either another variety or at least the same family. The one downside of the existing plantings is that variety is scattershot. The new planting will help to cut down on some noise. That being said, this study is focused on temperature protection and phenological acceleration regardless of variety.

The temperature probes used for this proposal are made by Ambient Weather/Ecowitt and connect with a sensor hub/monitor via radio wave. The sensor hub/monitor connects to the internet via Wi-Fi and results are available, and recorded, by the minute. There is no local backup of data in the event of Wi-Fi failure. This is potentially problematic but keeps the cost of the project down. Temperature probes will be placed outside of the tunnels, within the tunnel between the interior and exterior hoops, and within the interior hoop if that hoop exists. I will attempt to protect the probes from solar radiation throwing off the temperature during the day by shielding them. The recorded temperature data will be analyzed, comparing lowest, highest, and average temperature experienced. This data can be used to make a growing degree days chart for each treatment, showing the presumed acceleration of ripening through materials used. These probes also measure humidity, so dew point can be calculated. The temperature data from the probe placed outside the tunnels will be corroborated by the closest available weather station.

The material coverings will be applied in the fall when the forecast shows consistent sub-freezing temperatures, or a low under 25F. My guess is early December. The materials will be removed in the spring, from the interior materials to the exterior materials, as the shoots of the tree threaten to touch each layer. If temperatures reach over 95F in the spring, the tunnels will need to be vented by pulling up the plastic on the sides.

Phenology will be recorded first by counting the number of buds left post-pruning and tying to the low cordon system. My goal is 12-15 viable shoots per mature tree. I may leave slightly more, anticipating some damage, then prune those away in the spring with bud emergence. The buds that emerge as viable shoots during bud break will be counted to see how well the protection worked. Any frost damage incurred from advancing bud break through the protection materials will be noted. The date of bud break will be recorded for each tree, in each treatment as well. Next, when figs first form by tree will be recorded. After that, the date on which the first ripe fig is picked will be recorded. Each tree will be tracked by harvest to show total figs per tree over the course of the season. A five to ten fig sample of each variety will be used to find average fig weight so yield weight can be estimated. Pruning weights will be taken in November, before installing the protection materials, to see if the (presumed) phenological boost affected the total growth of each tree. Any unanticipated results that may have a relationship to the protection scheme will be recorded.

Research progress 2021-2022

While my project didn't receive funding until the end of March of 2021 I did have aspects of the project proposal in place prior to funding so I will briefly discuss the results of my protection schemes from winter 2020-2021 as they have bearing on my phenological recording during the growing season of 2021; they also informed my protection scheme for this winter (2021-2022).

Protection 2020-2021

@Site A (Waterloo, NY), 1 tunnel (12 trees)

Clear Poly (6mil) + Clear Poly (4mil) + Row Cover (1.5oz)

@Site B (Dresden, NY), 2 tunnels (24 trees)

North Tunnel- Clear Poly (6 mil) + Clear Poly (4mil)

South Tunnel- Clear Poly (6 mil) + Mylar (2 mil)

The site A tunnel was partially protected on 12/11/20 (outside, clear poly layer only). Site B tunnels were fully covered on 12/23/20 while the site A tunnel was fully covered on 12/24/20. 

Phenology 2021 Growing Season

Budswell was observed towards the end of March and by 4/9/21 a few buds close to the ground had just opened. Despite these early signs, and congruent with the cool April of 2021, the trees really didn’t experience budbreak till close to 5/1/21. And even then they didn’t pick up much steam until about the second week of May. This can be attributed to possible vascular damage from impaired cold hardiness, as well as the cool spring temperatures.

The first fig primordia (bumps before figs emerge from shoot) were observed on 5/31/21 on the early varieties (mostly Mt Etnas like Chicago Hardy). At 6/15/21 the early varieties were at pea size while fig primordial bumps were observed on the later varieties like Galbun, Gros Monstrueuse and Lebanese Red. By 6/29/21 the early varieties were at cherry size, which is very close to lag phase, while the late varieties were at pea size. By 7/9/21 most later varieties had reached cherry size.

On 8/30/21 the first color change was observed on a Chicago Hardy tree at Site B. Color change was then seen on a somewhat later variety (Giant Amber) on 9/5/21 at Site A. Sometime between 8/30/21 and 9/5/21 the first ripe figs were enjoyed by a non-human. As a reference point, the first ripe figs from potted fig trees not associated with this project were enjoyed on 8/7/21. On 9/20/21 the first VdB showed color change. On 10/10/21 the first Galbun was ready for harvest. On 10/15/21 the first AJH ripened (tied with VdB for last to ripen in most years).  

Ideal Tree Case Study 2021

At Site B one tree, a Graye’s Greenhouse (heirloom fig from Mt Etna family), came through the winter with little damage. This tree was observed as an ideal case study on 9/28/21. It had two trunks and one retained sucker to be used as a possible renewal trunk. There were four shoots on one trunk, and seven on the other. From the shoots, including the renewal, 181 figs were counted as being at cherry size or larger. I’m using cherry size as a proxy for the figs being at lag phase. I think 20 figs were already picked by this time, meaning this tree set 201 figs total.

On 11/04/21 this tree was observed as having 83 figs at cherry size left unripened. It stands to reason that between 9/28/21 and 11/04/21 close to 100 figs were picked off this tree.

The full data can be viewed here- https://docs.google.com/spreadsheets/d/1nK3NRFfyOtA3xm4PgP4MBeMI02oc4LrG8mnQXYlbkfY/edit?usp=sharing

Harvest Notes 2021

Around 40-50 figs were left unripened on Gros Monstrueuse. Around 40 ripe figs were picked off four VdB trees. These trees did not benefit from a head start (phenological acceleration) in the spring from the protection materials, in fact they suffered due to the protection materials due to compromised cold hardiness, and struggled to ripen figs in the limited zone 6a season. For anyone planting I’d concentrate on planting early varieties unless the late varieties pull a premium to make up for lack of production. I hope that I’ll see better results (i.e. accelerated growth) this spring with better protection materials.

Pruning Weights 2021

I don’t think too much can be gleaned from this data except that trees that survived the winter better produced more wood in the growing season. The ideal case study tree, Graye’s Greenhouse, grew 5.75 pounds of wood in the 2021 growing season. The average for the site B south tunnel (without Graye’s) was 1.6 pounds, while the north tunnel was 1.48 pounds. The trees at colder Site A, having taken more damage, produced an average of 1.09 pounds per tree.

Full data available here- https://docs.google.com/spreadsheets/d/1nK3NRFfyOtA3xm4PgP4MBeMI02oc4LrG8mnQXYlbkfY/edit?usp=sharing

Tunnel Construction 2021

A new fig tunnel, site B middle, was planted around 6/1/21. It has six trees of one variety, and six that are from the same family (Mt Etna). This uniformity should lend itself to data comparison. All 12 of these trees are early ripening, which should help production. The construction of this tunnel was slightly different than the previous three. Rebar stakes were driven into the ground, and the EMT hoops were placed onto the rebar. The rebar and EMT were joined by EMT couplers. Unlike previous tunnels, the landscape fabric was laid down prior to planting in the spring (much easier than retrofitting). This tunnel, Site B north, and the tunnel at Site A, use a draping wire for the inner protection layer. Site B South uses small hoops made from nine gauge vineyard wire. All tunnels now have a “purlin” wire that runs through the EMT hoop at its apex and is secured to the end posts. This prevents the hoops from wiggling free from where they’re attached to their stakes.

Unfortunately, lack luster planning and a late grape harvest season pushed back the completion of this tunnel until 12/27/21. Protection was put into place at all tunnels by 12/27/21, but was not fully buttoned up until 1/7/22. Supply chain issues delayed the placement and activation of temperature sensors until 1/8/22 at Site A and 1/15/22 at Site B.

Protection 2021-2022

Site A- Clear Poly (6 mil) + Row Cover (1.5oz)

Site B, South- White Poly (4 mil) + Mylar (7 mil)

Site B, Middle- Clear Poly (6 mil) + Mylar (7 mil)

Site B, North- White Poly (4 mil) + Clear Poly (4 mil)

This setup will allow us to decouple the influence of the white poly, outer, and mylar, inner, layers. Unlike the mylar from the 2020-2021 season, this mylar is white on one side. The reflective side was faced inward, to retain the ground heat. We’ll see how the white outside layer does in reducing heat spikes from the winter sun.

2022-2023 Disasters and Pivoting

During the winter of 2021-2022 voles damaged or destroyed 90% of the fig trees overall, and 100% at the Dresden location. Around 1/3 of the trees in Dresden were not salvageable and had to be replaced in the spring of 2022. The remaining 2/3rds were set back to the soil line due to girdling. Some trunks may have suffered winter damage in addition but it was difficult to decouple the two effects. My best guess is that the cozy conditions of the low tunnels caused first a slow build up (the first few winters) then an explosion of the vole population (2021-2022 winter). The sheer numbers of the voles prevented their control by poison alone, and encouraged feeding on the fig trunks due to competition and food scarcity.

Some relevant data was collected by the temperature sensors which will be discussed in the results section, but from a farming perspective the voles effectively killed any hopes for growing season research--recording pruning weights, phenology dates, or crop weights and counts. With this in mind I pivoted this project to paying more attention to vole protection, and a discussion of what went wrong. 

Mid fall vole damage on fig trunk.Mid fall vole damage on fig trunk.

Vole damage to fig trunk.Vole tunneling under landscape fabric.Replacement figs waiting for their planting date.

Landscape Fabric

After the full scope of the destruction caused by the voles became apparent in the spring my first move was to remove the landscape fabric. My original idea forthe fabric was to warm up the soil, accelerating phenology, and keep the weeds at bay since as a side project I'm not always able to devote as much time to the figs as I'd like. Unfortunately, it proved an ideal habitat for the voles. Upon removal I found extensive tunneling, often leading up to, under, and through the roots of the fig trees. I left landscape fabric on one fig tunnel row (out of the four total) as a "high pressure control" of sorts, to see if my other vole damage prevention measures are enough on their own. In the 2022 growing season weeds were controlled with a combination of weed whacking and contact (non systemic) herbicides. The landscape fabric did seem to encourage a strong native snake population, but unfortunately they aren't active during the winter when we need their help.

Evidence of snakes living under the landscape fabric.Early vole damage on trunks.Extensive vole tunneling.

Vole Protection 2022 Edition

Previously my vole protection consisted of PVC bait stations filled with zinc phosphide bait, generally two per 100 foot tunnel, and hardware cloth around at least 50% of the trunks for each tree. After watching the voles dig under the hardware cloth, first eating through the roots and then emerging to girdle the trunk, I decided to ditch this method entirely. I do think it could be effective if you are able to place the hardware cloth deep enough at the same time as planting the tree--but it would need to be wide enough to accommodate future growth. In the late summer of 2022 I started overhauling the vole protection program by first digging around the root ball of each tree. I removed as much dirt as I could then back filled with no.2 stone. The idea being that the voles would be discouraged by trying to dig through the stones and find easier meals. That left above ground protection, which I attempted to solve by painting the trunks with a paint and castor oil mix. I used interior latex as it's supposed to be both persistent and permeable. Castor oil is supposed to be a strong rodent repellent. I did not dilute the paint and the ratio was something like 5:1 paint to oil (this is significantly more oil than recommended but their use cases weren't with paint). A few extra trunks were left unpainted as a poor man's control for this experiment. And again one tunnel at the Dresden location still has landscape fabric so it's the "high pressure control" of sorts. The bait stations will be refilled more aggressively over the winter of 2022-2023 than they've been in the past. 

Step 1: Digging out the root ball before filling back with rocks.Step 2: Halfway through filling in root mass with rocks.Step 4: Latex paint and castor oil for vole protection.Another example of vole protection, multi trunk.

2022 Changes to Low Tunnels

A few changes were made to the low tunnels at both locations in preparation for the 2022-2023 winter. The clear poly used for the 2021-2022 winter at Dresden was 2 mil overwintering clear plastic instead of the intended 6 mil clear plastic. This was a bone headed mistake and will be discussed further in the discussion section. So this winter the correct 6 mil clear poly is in place. No row cover will be used this year at the Waterloo tunnel location. Instead, a double outer layer (white 2 mil overwintering plastic, then 6 mil clear poly inside) is in place, with an inner layer of mylar.

At the Dresden location the north most tunnel suffered extensive wind damage in the fall when covering materials were left attached to the ends but not secured to the individual hoops. In response, I took down all the hoops and am instead calling the north tunnel the low-low tunnel as it's a 20 inch tall triangle shape (the regular hoop tunnels are 42" tall). This tunnel has two layers: white 2 mil overwintering plastic, then 6 mil clear poly. Both layers have been doubled up by folding them over top of themselves, and secured using tarp clamps and vineyard wire. If temperature data shows this method to be beneficial it's an attractive and simple alternative to the EMT hoops which require several onerous steps before and during setup. 

Misc Notes: Irrigation stakes (1/2") are a cheap and useful option for anchoring the plastic to the ground, especially next to where the rope tie downs are secured as that creates a natural gap. The tunnel ends have always been tricky to secure and I've found spring clamps to be simple and effective. In the summer of 2022 I left some of the covering materials in the field by securing them to the purlin wire that connects the EMT hoops. They didn't suffer any significant damage though they would sometimes fill with rain water (I found tying them tight together to the wire at least once between the hoops to help cut down on this). It did make the fall covering easier, though it likely shortens the lifespan of the covering materials. 

Wind damage of low tunnels.Wind damaged low tunnel.Tarp clamps, useful for securing covers to wire.Replacement trees lined up ready for new homes.



Research results and discussion:

Results & Discussion 2021

Temperature data is only available for site A. The lowest recorded temperature that the fig trees experienced under the inner layer of protection was 13.5F on 1/30/21 when the outside ambient temperature hit -1.3F. On 12/18/20 the trees experienced 15.3F while outside it was 3.6F. I mention that because the trees only had one layer of protection and in mid-December they may not have been at peak cold hardiness.

Snow cover heavily influenced the level of protection. For example, on 2/20/21 site A received around eight inches of snow. On 2/21/21 the outside temperature dropped to 0.7F while under the inner protection the figs enjoyed a balmy 30F. When time permitted I tried to bolster this affect by mounding snow onto the tunnel using a snowblower. In contrast, on 1/9/21 with no snow cover the difference between outside (15.4F) and the inner layer (18.9F) was only 3.5 degrees.

The full data set and charts can be accessed here-- https://docs.google.com/spreadsheets/d/1DZWZkTFkATfm0AITchveZ5xHrkKgEyjMJv-Ui5WZIOI/edit?usp=sharing

For protection from deep winter lows the protection scheme of layers of clear poly worked very well. Fig trees should be able to survive 13.5F with low/acceptable levels of damage that can be worked around by leaving extra buds and canes. Unfortunately the clear poly also resulted in sharp spikes in temperature on sunny winter days that very likely disrupted the cold hardiness of the fig trees and may have also resulted in some trunk cracking. For example, on five separate days in January the innermost layer of protection recorded higher than 90F. In the spring, most trees showed heavy signs of damage. Most died to their trunks (around 12 inches off the ground), while some died to the ground. No trees died outright. The only exceptions were the trees on the outside of the tunnels, which may have resulted from air infiltration due to poor sealing. The trees at Site B with the mylar inner protection layer fared better than the other tunnels as well. I suspect the reflective properties of the mylar mitigated the heat spikes while also reflecting ground heat.

These results motivated the PI to change the materials used for the winter of 2021-2022 to include white poly to decrease the chances of temperature spikes on sunny winter days.

Initial Results, Winter 2021-2022

As noted above data collection for winter temperature readings did not commence until 1/8/22 at Site A and 1/15/22 at Site B. Initial low temperature recordings at Site A are discouraging.

1/11/22, 3am. Outside Temp: 7.0F. Outer Layer: 8.0F. Inner Layer: 12.4F

1/15/22, 3am. Outside Temp: 0.7F. Outer Layer: 5.3F. Inner Layer: 8.5F

1/15/22, 11pm. Outside Temp: -2.1F. Outer Layer: 0.3F. Inner Layer: 5.3F.

So the fig trees at Site A have already experienced a much lower temperature (5.3F) than they did in the winter of 2020-2021 (13.F). Also problematically, the trees have experienced temperatures over 67F on four days already (though only one day over 80F).

From just two days of real data from Site B no interpretations should be ventured. But venture I shall. The daytime data is encouraging. The outer white poly stayed 3-6 degrees cooler than the clear poly outer layer. The mylar inner layers actually read cooler than the outer (between layers) probes, suggesting the mylar material was actually reflecting the coolness of the partially frozen ground. Unfortunately the inner layers recorded abysmal temperatures on the morning of 1/16/22. The south tunnel read 0.9F, the middle -1.8F, and the north 3.6F. If these were true readings it would be likely that all trees will be reset to the ground. I’m holding out hope it was some kind of fluke due to radiative cooling or the sensors hadn’t grown their winter skin yet.

Photos available here-- https://photos.app.goo.gl/ChgKbTAYxUdAEays9

2021-2022 Winter Results and Discussion

Sensor Issues

For this study I used a combination of Ambient Weather and Ecowitt wifi gateways and sensors (they appear to be the same hardware). The gateway unit needs a wifi connection to log the data and the sensors need to be within radio range (around 300 feet). The benefit to using this setup is that it is very inexpensive, can be monitored on the fly, saves to the cloud, and can be setup with temperature alerts (helpful for say greenhouse growers who can turn on a heater, aka do something other than chew on their nails). I ran into several of the drawbacks, however. For one, both of my growing locations were farther than 300 feet. At the Dresden location this meant that the closest tunnel uploaded data the most consistently and the farthest was the least reliable. Using lithium AA was a big help but at low temperature the sensors could become less reliable (just when you want them to be the most reliable).

Using mylar as one of my covering materials caused interference rendering the normal sensors useless. The work around is to use sensors that have a wired probe so you can put the sensor body outside of the mylar but have the probe measure the temperature under the covering. This works great until rodents start chewing on the wires. This happened multiple times over the course of the winter. 

Alternatives to these sensors seem to be coming into more widespread use. SensorPush makes a bluetooth connectable sensor that uploads its data once you come within bluetooth range. At the moment they're too expensive for widespread use ($90/piece, the Ambient/Ecowitt sensors are $15-20/piece), but the price may fall. 

Cold Temperatures and Low Tunnel Materials

The right combination of materials for protection of fig trees (or any sensitive plants) from winter low temperatures remains elusive but mylar is cementing itself as part of the solution. Greenhouse plastic, whether 6 mil poly or 2 mil white overwintering poly, has performed in an underwhelming fashion and the temperature sensors have even reported figures below ambient temperature perhaps due to radiative cooling (where IR waves escape at a disproportionate rate due to the transparency of the plastic). Whereas clear 6 mil or 2 white 2 mil poly had a minor effect on temperature (between -2.2 and +2.6F difference), mylar had a consistently positive effect generally adding 6-7 degrees over ambient temperatures in four different cold episodes between 1/22/22 and 3/4/22. Sensor malfunctions prevented data from all materials being compared in some cases but in all cases some contrast was evident between the temperature under the mylar and outside of the mylar. 

WP=white poly. MY=Mylar. CP=Clear Poly. 

Location Date Tunnel Material Temp (F) Diff from Amb
Diff from Outer Material
ARWC 1/22/2022 South WP -8.00 0.50  
ARWC 1/22/2022 South WP+MY -1.30 7.20 6.70
ARWC 1/22/2022 Mid CP -10.70 -2.20  
ARWC 1/22/2022 Mid CP+MY -2.40 6.10 8.30
ARWC 1/22/2022 North WP -4.60 3.90  
ARWC 1/22/2022 North WP+CP -4.00 4.50 0.60
ARWC 1/22/2022 Ambient Ambient -8.50    
Location Date Tunnel Material Temp (F) Diff from Amb
Diff from Outer Material
ARWC 2/5/2022 South WP 4.80 2.20  
ARWC 2/5/2022 South WP+MY 9.50 6.90 4.70
ARWC 2/5/2022 Mid CP 5.20 2.60  
ARWC 2/5/2022 Mid CP+MY 9.50 6.90 4.30
ARWC 2/5/2022 North WP 5.70 3.10  
ARWC 2/5/2022 North WP+CP      
ARWC 2/5/2022 Ambient Ambient -2.60    
Location Date Tunnel Material Temp (F) Diff from Amb
Diff from Outer Material
ARWC 2/14/2022 South WP 0.90 -1.80  
ARWC 2/14/2022 South WP+MY 6.60 3.90 5.70
ARWC 2/14/2022 Mid CP -1.80 -0.90  
ARWC 2/14/2022 Mid CP+MY 0.70 -2.00 -1.10
ARWC 2/14/2022 North WP -2.20 -0.50  
ARWC 2/14/2022 North WP+CP      
ARWC 2/14/2022 Ambient Ambient 2.70    
Location Date Tunnel Material Temp (F) Diff from Amb
Diff from Outer Material
ARWC 3/4/2022 South WP 7.20 0.00  
ARWC 3/4/2022 South WP+MY 11.80 4.60 4.60
ARWC 3/4/2022 Mid CP 1.60 -5.60  
ARWC 3/4/2022 Mid CP+MY 9.90 2.70 8.30
ARWC 3/4/2022 North WP 3.70 -3.50  
ARWC 3/4/2022 North WP+CP      
ARWC 3/4/2022 Ambient Ambient 7.20    

The other consistently positive covering material in this study has been snow. At site B (in Waterloo, NY) I was able to use a snowblower to cover or seal the edges of the low tunnels when snow was available. The results stand out as outliers when looking through the data. Similar cold temperatures were experienced on 1/26/22 and 2/5/22 but the results are markedly different due to the influence of snow cover. Seen below, it looks like even partial insulation by snow could be responsible for as much as a 14 degree increase. 

RC=Row Cover

Location Date Tunnel Material Temp (F) Diff from Amb
Diff from Outer Material
Waterloo 1/26/2022 Back CP 2.7 11.4  
  1/26/2022 Back CP+(WP+RC) 11.1 19.8 8.4
  1/26/2022 Ambient Ambient -8.7    
Location Date Tunnel Material Temp (F) Diff from Amb
Diff from Outer Material
Waterloo 2/5/2022 Back CP 16.2 25  
  2/5/2022 Back CP+(WP+RC) 19.8 28.6 3.6
  2/5/2022 Ambient Ambient -8.8    

This effect of snow can also be seen when contrasting the effects of covering materials at the two different sites. Between 2/14/22 and 2/15/22 Dresden experienced a low of 2.7F while Waterloo experienced -1.0F. The cumulative covering materials in Waterloo bumped the temperature up 12.7F, while in Dresden similar materials only boosted the temperature 3.9F--the sole difference being the level of snow built up around each tunnel. 

Location Date Tunnel Material Temp (F) Diff from Amb
Diff from Outer Material
Waterloo 2/15/2022 Back CP 5.4 6.4  
  2/15/2022 Back CP+(WP+RC) 11.7 12.7 6.3
  2/15/2022 Ambient Ambient -1    

Snow cover at the Dresden fig tunnel.Using a snowblower to increase fig tunnel insulation value.

Overall, while it seems like mylar is part of the solution further research into better insulating materials is needed. Vegetable farmers often use a heavy felt material to cover their fragile greens in the spring, these kind of textiles could work well in tandem with an outside layer of plastic to keep them dry and hoops or a draping wire to support their weight. Organic materials like composting leaves could also play some role, particularly in sealing the edges of the tunnels. 

Hot Temperatures and Low Tunnel Materials

While not as obvious as the damage caused by voles and cold temperatures, damage to fig trees caused by heat should be a strong consideration for materials selection in a low tunnel system. The temperature spikes caused by a greenhouse effect with clear poly can wreck havoc on the cold hardiness of perennials and can also throw off your data analysis. On average, the covering materials for the Waterloo fig tunnel increased the temperature roughly between 7 and 10 degrees over ambient in January 2022. That sounds great. Except that much of that temperature boost may come from the afternoon sun, wasted heat that is possibly detrimental to the cold hardiness of the trees. 

Location Month Tunnel Material Avg Temp Avg High Temp Avg Diff from Amb Avg H Diff from Amb
Waterloo Jan Back CP 25.51 33.44 6.91 10.99
Waterloo Jan Back CP+(WP+RC) 28.58 36.12 9.98 13.67
Waterloo Jan Ambient Ambient 18.6 22.45 0 0

Another way to quantify this is to count the number of times the temperatures under the covers exceeded 60F. While this could be beneficial to getting off to a strong start later in the spring, in the winter it may pull the trees out of dormancy right in time for a killing cold snap. Below is a count (each count represents a four hour increment) of the times the temperature exceeded 60F between January and March. 

        4 HR Increments  
Location Month Tunnel Material CT: Times above 60F Avg Temp
CT: Times above 60F Avg H Temp
ARWC Jan South WP 0 0
ARWC Jan South WP+MY 0 0
ARWC Jan Mid CP 1 3
ARWC Jan Mid CP+MY 0 0
ARWC Jan North WP 0 0
ARWC Jan North WP+CP 1 1
ARWC Jan Ambient Ambient 0 0
        4 HR Increments  
Location Month Tunnel Material CT: Times above 60F Avg Temp
CT: Times above 60F Avg H Temp
ARWC Feb South WP 2 18
ARWC Feb South WP+MY 0 2
ARWC Feb Mid CP 8 29
ARWC Feb Mid CP+MY 3 9
ARWC Feb North WP 3 15
ARWC Feb North WP+CP - -
ARWC Feb Ambient Ambient 0 5
        4 HR Increments  
Location Month Tunnel Material CT: Times above 60F Avg Temp
CT: Times above 60F Avg H Temp
ARWC March South WP 32 61
ARWC March South WP+MY 15 34
ARWC March Mid CP 35 64
ARWC March Mid CP+MY - -
ARWC March North WP 29 52
ARWC March North WP+CP 26 40
ARWC March Ambient Ambient 11 20
        4 HR Increments  
Location Month Tunnel Material CT: Times above 60F Avg Temp
CT: Times above 60F Avg H Temp
Waterloo Jan Back CP 2 11
Waterloo Jan Back CP+(WP+RC) 2 18
Waterloo Jan Ambient Ambient 0 0
        4 HR Increments  
Location Month Tunnel Material CT: Times above 60F Avg Temp
CT: Times above 60F Avg H Temp
Waterloo Feb Back CP 8 32
Waterloo Feb Back CP+(WP+RC) 12 30
Waterloo Feb Ambient Ambient 1 1
        4 HR Increments  
Location Month Tunnel Material CT: Times above 60F Avg Temp
CT: Times above 60F Avg H Temp
Waterloo March Back CP 34 62
Waterloo March Back CP+(WP+RC) 39 66
Waterloo March Ambient Ambient 9 20

Gleaning through this data, it's immediately evident how detrimental clear poly can be while mylar has a strong mitigating effect on temperature spikes. It's also readily apparent how the sun picks up steam in the second half of February and has a very strong effect in March. Growers should consider venting their tunnels on sunny days late in February and certainly in March. There may be a point in March in which killing winter temperatures for figs is passed (mid-March), in which case removing the materials altogether is an option. This would prevent early wake up (when desired) and any preserve any remaining cold hardiness.

There is a material used in greenhouses that consists of alternating strips of clear poly and foil to retain heat. For a low tunnel it could also be used to reflect away excess sunlight. Another option is to spray on an overwintering paint, another technique used by some greenhouse growers. The overwintering white poly had a lesser effect than expected so outside of mylar the search continues. 

Vole Protection Revisited

While we're only a few months into the winter of 2022-2023 the results of our redesigned vole protection have been encouraging. First, it's important to note that rabbits and voles are not the same (:P). Rabbits have continued to do damage to the fig trunks regardless of whether they were painted or not. While rabbits do not seem to dig under the tunnel materials, and thus are excluded by them, they often do their damage in the fall before the covers are applied. The good news is that the stones seem to be discouraging the voles from digging around the root mass and the paint is repelling them from eating the trunks. WOOOOO. There is evidence of vole tunneling, especially around the bait traps, suggesting they are taking the bait. Several vole corpses have been discovered too, RIP. All that said I haven't had a chance to check the high pressure tunnel (landscape fabric remains), and there are plenty of months to go. It also looks like the paint is starting to degrade and there is evidence of the voles nibbling on trunks that did not get painted. We shall see. The first picture is of a shallow vole hole in the no 2 stone. 

Shallow vole hole.Vole tunnels near bait station and untouched trunk in background.Small (vole) nibble on unprotected section of fig trunk where paint didn't reach.Rabbit damage (vole and rabbit protection do not overlap much).Fig canes being tied out along the wire before winter covers go over.

The Fig Market

While the in ground fig trees that are the subject of this study contributed very little to fig sales in the fall of 2022, the potted trees and in ground in the greenhouse trees had a banner year. Around 40 pints were sold through a winery tasting room, on display in a case next to cheese and white wine bottles. About 25 quarts were sold to a local restaurant who used them mainly for a fig, cheddar and bacon flatbread (yum). A couple bags of fig leaves and around 6 quarts were also sold to a winebar, which made a fig negroni by soaking the leaves in gin and using the fig fruit in a sweet vermouth. With the production potential of in ground figs, wholesale opportunities will have to be explored in the future. Collaborations with local breweries and wineries--maybe a Fig Field Day in the early fall--are another possibility. Fig cutting sales in the winter of 2022-2023 have been particularly strong and represent a nice no waste opportunity--and help spread the fig gospel to future growers. 

Figs in pints ready for sale.


Participation Summary
1 Farmers participating in research

Education & Outreach Activities and Participation Summary

1 On-farm demonstrations
1 Tours
1 Workshop field days

Participation Summary:

24 Farmers participated
4 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

Fig open house flyer.

On Friday, November 18th 2022 I hosted an open house/demonstration day at Stark Street Gardens in Waterloo, NY. This day was designed to be fairly informal with a tour of the different aspects of Annelise Farms, and methods of growing fig trees, with a small tasting of figs (provided by Seneca County Cooperative Extension, along with nutrition information) and cider from Lake Drum Brewing available for pairing. Local growers and curious public showed up to pepper me with questions--everything from overwintering techniques to preferred potting media for rooting cuttings to "why figs?" Four members of Seneca County Cooperative Extension, including their director Ave Bauder, assisted with setup and support but for the most part it was a one person show. 

First we toured the potted fig trees which had mostly gone through senescence. This was followed by a tour through the greenhouse and a discussion of the challenges and benefits of growing in greenhouses in general, and any aspects specific to figs. Next we toured the outdoor in-ground figs and discussed my low tunnel techniques for overwintering. This mostly ended up centering on protection against voles. Finally we returned to the fire to warm up and try some dried figs prepared by Seneca County Cooperative Extension and some delicious cider provided by Lake Drum Brewing. Here we discussed some of the business aspects of growing figs and any questions I had failed to answer up to this point. 

The open house was a great success and the large turnout (20-25 people not including myself or Seneca CCE members) had me thinking of putting on a similar activity a little earlier in the fall next year (while fresh figs are still available). I hope I answered enough questions to satisfy or pique curiosity in growing these challenging but rewarding fruits we call figs. 

Picture of participants at fig open house 11/18/22. Picture of participants at fig open house 11/18/22.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.