A Comparison of the Profitability of Subsoil Heated and Unheated Hoophouse vs. Field Production of Cool-Climate Salad Crops in Central Lower Michigan

Final Report for FNC04-530

Project Type: Farmer/Rancher
Funds awarded in 2004: $3,033.00
Projected End Date: 12/31/2007
Matching Non-Federal Funds: $4,606.55
Region: North Central
State: Michigan
Project Coordinator:
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Project Information


Project Background:

The project was conducted at Wildflower Organic Farm, of Bath, Michigan, a family operated farm. The farm is located 10 miles northeast of Lansing, Michigan. The land is rolling and soils are either deep glacial sandy loams or loamy sands. Applications of compost are necessary to increase water holding capacity, mineral availability and enhance soil ecology. We grow and sell organic vegetables, fruit and flowers on 3 acres of land. Markets include subscription CSA, two local farmers markets (Lansing and Okemos, MI), restaurants, a local distributor and a grocery store (East Lansing Food Co-op). This project was initiated because of a need to optimize production and revenue from our limited land area, and over time by extending the season.

Project Description and Results:

Project goals:
The use of unheated plastic film hoop-houses, also called high tunnels (essentially a low tech greenhouse) over natural soil for production of cool season vegetables, nearly year-round, in central-lower Michigan and at similar latitudes has recently been demonstrated.

This technology offers the possibility for small farms to produce over a longer period of the year and potentially increase profits in the off-season. Such production may result in increased farm profitability while increasing the availability of locally marketed food. It is important to realize, however, that actual profitability using such technology has not been clearly compared to field culture and remains a critical component in the decision to adopt it. What are the actual net profit differences? This project addresses the question of net profitability of the a) cool-season hoophouse method of production, compared to, b) conventional field culture and in, c) a seasonally heated greenhouse. Profitability was addressed in the context of the various markets utilized and was compared and contrasted.

As stated, this project utilized three production methods to compare yields of cool season crops and profitability. It was decided that the comparison would focus on mixed lettuces (All-Star Gourmet Mix, Johnny’s Selected Seeds) and Komatsuna, since these two are reliable and consistent crops to grow and they are easy to distribute/market. Because of soil/site variability and differences in timing of crop planting and harvest under heated, unheated and field culture and without replications and statistical analyses, strict comparisons can’t be made, however, we were able to draw meaningful conclusions based on cropping period made possible, yield results and costs of production under each of the three methods.

Temperature differences were large between the three methods and it was hoped that that would override the other factors. Lettuce and komatsuna (a mustard) is harvested repeatedly from the same planting (often termed “cut and come again”) over a period of time as weather and the physiology of the plant allow. As temperatures increase in the summer, food quality is often reduced as these greens tend to become bitter, and the plants flower and begin their reproduction.

Yield data is presented is on a per foot of row basis with total combined yields over the season for each of the three growing areas.

Treatments were not replicated.

Production method a) unheated hoop-house: The initial concern was for site preparation. First, the site was cleared of brush. Next, topography at our farm is rolling, so it was necessary to do a rough grading with a bulldozer which entailed removing some topsoil from one area and moving it to a lower area on the hoop-house site. Next, ground elevation was measured with a land surveying level. The final leveling of soil was done by adding topsoil to low areas, using a tractor with a front-end loader. This site then required a bit of remediation after land leveling disturbances of the earth.

Since some topsoil was removed through rough grading (up to 8” on the south side) intensive applications of compost were applied, around 60 tons to the acre equivalent using horse manure/sawdust compost, straw/cow manure compost and chicken manure compost. Other amendments, including the equivalent of from 900 to 1800 lbs. per acre, rock phosphate, green sand and azomite were applied to enhance or maintain nutrient levels over time. After amendments were applied, materials were incorporated and deep tillage was done with a Granholm plow, which is essentially a very large moldboard plow. The site was then disked and allowed to settle.

Construction of the unheated hoop-house was completed in Fall 2005. It consists of a 26 by 96 foot round style frame covered by a single layer of 6 mil UV resistant polyethylene. This hoop-house incorporates wire and track fastening of plastic, which makes installation and adjustments such as tightening much easier (less labor cost) is long lasting and moderate in cost. It also utilizes roll-up sides for ventilation, negating the need for fans or electrical power.

After cropping spring 2006 the site was kept weed/plant free through cultivation with a troybilt rototiller until August, to reduce weed pressure (sterile fallow) notably, jimpsonweed from horse manure compost. Mid-summer the hoop-house space was again amended with 1-2 inches in depth of horse manure/sawdust compost and 100 lbs of chicken compost for a nitrogen equivalent of around 50 lbs/acre. Materials were incorporated with a rototiller.

Finally, August 25, 2006 crops were planted that included mixed lettuces and the mustard green, Komatsuna.

Lettuce planted Fall 2005 emerged poorly so no data was collected.

Mixed lettuce (All-Star Gourmet Lettuce Mix, Johnny’s Selected seeds) was planted in 3 inch wide rows at 60 seeds per foot spaced 1 foot apart 9/10/06. Seedling emergence began approximately 5 days after planting. Harvest was conducted over a period between 10/28/06 and 1/2/07. Cuttings of lettuce totalled 0.18 lbs per foot of row or a total yield of 65 lbs over 360 feet of row (90 foot rows) during that period. Gradually cooling temperatures slowed growth. Additional significant cuttings will likely be possible through winter and spring months 2007 as temperatures are unseasonably mild.

Komatsuna was planted in four 90 foot rows spaced eight inches apart. Planting rate was 30 seeds per foot. The site was planted September 15, 2005. First harvest was 11/4/05 (0.15 lbs/foot), 12/2/06 (0.16 lbs/foot of row) and again 3/15/06 (0.16 lbs/foot) and 4/15/06 (0.18 lbs/foot). Total harvest was 0.65 lbs per foot of row from all four harvests combined or 234 lbs for 360 feet.

Komatsuna was planted same as above 8/25/06 for a fall crop. First cutting was 9/25/06 and last cutting was 12/27/06 and yield for that period was .0.58 lbs per foot or 209 lbs total from 360 feet.

Total for Fall 2005 through Winter 12/27/06 was 443 lbs or 1.2 lbs per foot.

Crops were protected during <25 degree temperatures inside the hoop-house using 0.5 oz./ sq. yard fabric row covers (Agri Bon inc.), supported over 10 gauge wire hoops. Production method b) conventional field culture: A site was selected near the other two hoop-house structures and similar in soil texture and aspect. This was an established garden site previously. Mixed lettuce (All-Star Gourmet Lettuce Mix, Johnny’s selected seeds) was planted in 3 inch wide rows at 60 seeds per foot. The bed consisted of four 30 foot rows spaced eight inches apart. First lettuce harvest was 5/25/06 and average yield was 0.12 lbs per foot of row. Total row footage harvested was 120 feet for a total of 14.4 lbs harvested. Second cutting was 6/15/06 at 0.10 lbs per foot of row and 12 lbs for the 120 feet of row. High Temperatures in July reduced flavor quality and the crop was removed from the bed. Total harvest was 26 lbs or 0.22 lbs/foot. Since lettuce eating quality is reduced mid-summer due to high soil temperatures a final outdoor lettuce planting was done on 8/25/06. A 1” layer of cow manure/straw compost was applied and incorporated in the soil using a rototiller prior to planting. Harvest was done on 10/10/06. Yield was 0.11 lbs per foot of row for a total of 13.2 lbs. A final harvest was completed 11/15/06 at 0.12 lbs per foot or 14.4 lbs total.
Total yield on the fall planting was 27.6 lbs. or 0.23 lbs/foot

Total harvest through the outside growing season (4 cuttings) on 120 feet of row (two plantings, spring and Late summer/fall) was 54 lbs or 0.45 lbs per foot of row.

Komatsuna was similarly planted 4/15/06 in four 30 foot rows spaced eight inches apart. Planting rate was 30 seeds per foot. First komatsuna harvest was 5/20/06 and yielded 0.14 lbs per foot of row for a total of 16.8 lbs. Second harvest was 6/15/06 and yield was 0.15 lbs/foot of row or 18 lbs for the plot. High temperatures caused the crop to bolt so it was removed. Total yield spring season was 34.8 lbs at 0.29 lbs per foot of row.

In Late August, a 1” layer of cow manure/straw compost was applied and incorporated with a rototiller. Planting again was done on 8/25/06. A first cutting was made 10/15/06 with yields at 0.15 lbs/ foot of row over 120 feet or 18 lbs. A second final harvest on 11/10/06 yielded 0.13 lbs per foot of row or 15.6 lbs for 120 feet of row. Total harvest on autumn planted Komatsuna was 33.6 lbs for the plot or 0..28 lbs/foot of row.

Total harvest outdoors of Komatsuna (Spring and fall crops combined) was 68.4 lbs or 0.57 lbs per foot of row.

Production method c) a seasonally heated greenhouse: The heated hoo-house is a 35 by 40 foot gothic style framed hoop-house covered with two layers of 6 mil UV resistant polyethylene. The greenhouse is heated using a propane fired forced air ceiling furnace. Fan ventilation is installed. Lettuce and Komatsuna was grown in raised beds constructed of 2 x 4 ‘s. Beds are approximately 15” in depth and are 25 feet in length and 3.5 to 4 feet in width. Soils are based on seedling mix of peat, compost, topsoil, sand, limestone, green sand azomite and rock phosphate.

Mixed lettuce (All-Star Gourmet Lettuce Mix, Johnny’s selected seeds) was planted on 10/5/05. The bed consisted of four 25 foot rows (100 ft.) spaced eight inches apart. Seeds were planted in 3 inch wide bands at 60 seeds per foot, with rows spaced eight inches apart

During the first week only, the hoop-house was heated to a minimum of 55 degrees to allow fast germination. Because of cool temperatures growth was slow. Starting 3/25/06 greenhouse temperatures were kept at a minimum 60 degrees F.

First harvest was 3/28/06. Yield was 0.155 lbs per foot of row or 15.5 lbs.. Yield on 4/8/06 was 10.5 lbs or 0.105 lbs per foot. On 4/20/06 11.5 lbs was harvested or .115 lbs/foot. On 5/6/06 11.5 lbs was harvested or .115 lbs/ft. The total was 0.6 lbs per foot or 60 lbs for this Autumn to Spring crop.

Komatsuna was similarly planted 10/5/05 in four 25 foot rows spaced eight inches apart in 3 inch wide bands at 30 seeds per foot, with rows spaced eight inches apart.
56 lbs or 0.56 lbs was harvested between 4/22/06 and 5/20/06. Total harvest was 0.52 per foot or 52 lbs. High temperatures shortened harvestable period.

Unheated Hoop-house,field culture, Heated greenhouse
Lettuce,0.18 lbs/ft. (fall/winter ’06 only)still being harvested, 0.22 & 0.23 or 0.45 lbs./ft total(Spring & fall’06),0.60 lbs/foot(Fall ‘05 -spring ‘06)
komatsuna,**0.65 and 0.58 or 1.2 total. Planted
fall ’05-sp., fall ’06-Winter), ***0.29 & 0.28 or 0 .57 total(Spring & fall ‘06),0.56lbs/foot
(Fall ‘05 -spring ‘06)

(Table 1.) Yield in pounds per foot of row.

* This represents only part of the growing cycle and harvest in the unheated hoop-house.
**0.65 in fall ’05 through spring ‘06. 0.58 Fall and winter
*** represents spring and fall crops combined

Results and discussion:
It’s difficult to ascribe yield differences under the three methods tested. Variables in timing of planting and harvesting, soil amendments, weather and response to temperature extremes all affected yield. This was designed as an experience and not a replicated experiment. That said, it’s fair to say that we typically have more reliable cropping and better yields in the hoop-house compared to field culture, therefore, it makes sense that yields trended higher under protection in this trial. The period of active growth that favors greens eating quality is longer and more controlled in the hoop-houses. Greens tend to grow best under fairly cool to moderate temperatures. The soils in both hoophouses and outdoors are well maintained, fertile, well drained and favor growth.

The main factor that stands out in this project is seasonality of harvest. There was some overlap in harvests in autumn, otherwise field culture and production in hoop-houses fell on opposite sides of the calendar. Film protection offers additional time for production. Thus the obvious payoff is in income produced beyond the usual outside crop year. But what were the costs of production?

Cost of the 26’ x 96’ frame, plastic and hardware was $2389.47 in 2005 (FarmTek Inc.). Additional costs of the structure itself went to 2 x 6 baseboard at $87.00 and side wall lumber at $48.00. Labor cost was around $1,000 (100 hrs at $10.00) and contracting for earth moving was $300.00. The total was $3834. (Note these are material and labor costs to install and not for additional data collection and analyses as shown in the final budget.)

Additional costs will be for poly film replacement and the labor to remove and attach it. Poly film may be replaced every 4 or 5 years. Cost of 1 layer of poly film is around $300.00 (2006). Removing and attaching film takes about five to ten hours (2 people working 2.5 or 5 hours for a labor value of $50.00 to $100.00). Total cost every four to five years is $400 to $450.

Because of incomplete lettuce yield data in the unheated hoop-house fall ‘05 to spring ‘06, results were inconclusive. If we look at yield looking across treatment methods outside and in the heated hoop-house (Table 1.), yields of 0.50 lbs per foot over the Fall to Spring season seem feasible, and are in the high range others have observed with the above methods.

The unheated hoop-house can accommodate 12 ninety foot rows with headspace and an aisle down the middle. Assuming 0.10 to 0.50 lbs yield/foot of row, yields would be 108 to 540 lbs. Current price for lettuce and mixed salad greens is $3.00 to $6.00 per pound. At a sale price of $5.00/lb, and the above yields, revenue would be $540.00 to $2700.00 per year, assuming a ready market.

Pay-off of initial investment would take from 2 to 8 years in those ranges if only lettuce were grown. In actual practice, a wider diversity of leafy crops is grown in the hoop-house (and elsewhere) to avoid growing more than can be sold based on consumer demand, and to use in value-added greens mixes. It is important to realize that during this pay-off period it’s possible that no additional revenue is gained from protection. Additional farm revenue comes after the pay-off period thus benefits are medium to long term if payed for at installation. Finance costs and profits could be analyzed based on terms of loans available.

There is also a period between mid June and late August when other short season crops like turnips or radish may be grown. Also there is the possibility to intercrop with, for example, pole beans or seedless cucumber. This would add additional revenue by incorporating the conventional outdoor growing season with fall to spring production.

For example, one 90-foot row of seedless cucumber can average 36 pounds per week ($55.00 sales) or roughly $200 – $250 per month of harvest for the season. This could last until mid- to late September. Greens cropping would follow. This is enough to pay off additional investment in 15 to 20 years just by itself. Labor and input costs (seeds, amendments tools etc.) would add up also, the same as would be incurred in an outdoor growing situation.

In 2005, a workshop on hoophouse production was organized through MSU-Extension and conducted by Susan Houghton of Giving Tree Farm. Part of the workshop included site preparation and was conducted at our farm.

In addition, results or this SARE project have been shared informally with Michigan State University students, some of whom helped erect the unheated hoophouse. Others who benefited included customers that visited on-farm to pick up produce and through the local grocery (East Lansing Food Co-Op) where we have marketed our produce during the winter with pictorial documentation.

Local producers who are considering use of hoop-houses for season extension or are currently using them have joined in informal discussions about use of this technology.

An open house to discuss results will be held Saturday, February 20, 2007. The notice has gone through MSU Extension (Vickie Marrone). Reporters will also be contacted and the general public will be invited in an open invitation through local news forums.


Participation Summary
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.