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
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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.

Introduction:

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.

Cooperators

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  • Judson Reid - Technical Advisor

Research

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

Location

SOP

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.

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

 

Participation Summary
1 Farmer participating in research
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.