Creating a Sustainable Year-Round Greenhouse Cropping System Using Straw-bale Culture and LED Lighting

Final Report for FNC09-747

Project Type: Farmer/Rancher
Funds awarded in 2009: $6,000.00
Projected End Date: 12/31/2011
Region: North Central
State: Minnesota
Project Coordinator:
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Project Information


[Editor's Note: To see this report with photos and with the tables properly formatted, see the PDF version of the report listed as an attachment.]

Little Foot Farm is a 35-acre farm that has 3 main enterprises: seasonal greenhouse business, perennial fruits and vegetables, and heritage breed pasture hogs. We manage all operations with an emphasis on sustainable and conscientious growing methods. We employ one part-time staff person. Most of our sales are direct marketed from the farm.

We have always employed sustainable practices for all of our operations. We grow all of our own greenhouse product, use bio-degradable containers, soy based fertilizers and organic products for pest and disease control. We do not use pesticides or herbicides on our fruits and vegetables and manage our hogs and chickens using Animal Welfare Institute standards.

GOALS: The goal of this project was to create and evaluate a year-round growing system that could utilize the traditionally dormant greenhouse seasons. The use of LED lighting and straw-bale culture was chosen as an alternative to traditional forms of greenhouse season extension such as plastic containers or in-ground growing, in an effort to minimize energy inputs and maximize cropping flexibility.

Layout and Schedule. The first task was to design the layout of the straw bales to create as much growing area as possible (230 sq. feet) in the greenhouse. See Attachment Number 1 as an example of our winter layout. We also wanted to establish a cropping schedule that would allow for 3 phases to be completed in a calendar year. Phase 1 would be June 1-October 15. Phase 2 would be a short season of Nov. 1-Jan.1. Phase 3 would be Jan. 15- May 15.

Establishing growing media to use on straw bales. We wanted to determine the best topdressing medium so that we could replicate year over year and have a baseline for making adjustments and controlling variables. The greenhouse was divided into 2 sections. In Phase 1, on Side A we used straight compost and on Side B we used Sunshine Organic Potting Mix and Sustane fertilizer. In Phase 2 and 3, bales on Side A were top dressed with Sunshine Natural and Organic Planting Mix and Paramount Green Pure Natural Organic Worm Castings while bales on Side B were top dressed with Sunshine Natural and Organic Planting Mix and Sustane Fertilizer. See Attachment Number 1 and Number 2.

Lighting. For Phase 1 (June-Oct15) we did not use supplemental lighting as day-length and light intensity was sufficient. In Phase 2, (Nov. 1-Jan.1) 25 Red, 220 diode, LED lights were arranged above the bales so that each light covered approximately 2 bales. The light came on at 3 pm and went off at 9 pm to create a total of 14 hours of light in the greenhouse (8 hours natural daylight and 6 hours LED lights). For Phase 3 (Jan 15-April 15) we focused on a more rigorous research process to determine the effects of different lighting treatments on the crop.

The greenhouse was arranged so that we could apply 3 different lighting treatments with four replications for each treatment. The treatments were: 4 red LED lights only; 2 full spectrum/blue LED and 3 red LED lights; and no LED lights. Mark Fleck, an LED expert with Grow with LEDs, was consulted to discuss the various treatment options. The lights come on at 4 am and turn off at 12 am for a total of 20 hrs of supplemental lighting. We chose this maximum amount of lighting based on previous research and the desire to maximize the differences in lighting treatments vs. no lighting.

Crops. A variety of crops were grown through the three Phases year 1. The Phase 1 (summer) trial included tomatoes, peppers and strawberries. The Phase 2 (fall/winter) crops included lettuce, arugula, carrots, beets, sugar snap peas, radishes, spinach and tatsoi. The Phase 3 (winter/spring) crop is exclusively sugar snap peas.

In year 2 we focused on just the crops that we felt had the potential to be economically viable so we grew sweet peppers during Phase 1 and sugar snap peas in Phase 2. We decided that heating the greenhouse in January and February was too economically risky regardless of the crop we chose, so we would limit non-bedding plant production to just summer thru late fall.

We received guidance from Prof. Bud Markhart as to both crop options for marketability, Mark
Fleck for advise on LED lighting options, and produce managers from both Mississippi market and the Wedge for guidance on pricing strategies and marketability of "out of season" or "first to market" products

(During the course of this project, I determined that the use of LED supplemental lighting as an input for the "out of season" production of sugar snap peas, was worthy of more detailed study. In doing so, I dovetailed my Masters Integrated Project with this SARE project. I presented the finding in a public forum in December of 2011 at the University of Minnesota. I have attached the full research project and slide presentation.)

Straw bales. While we began lying the bales with strings up, we eventually placed bales on their edges with the strings on the sides. With the twine on top, there was more degrading so that when bales had to be moved the twine would often break and replacement bales or reinforcement of some kind such as rebar pounded into the ground was required. This did influence moisture retention as water more easily penetrated through the bales oriented in this manner. Another drawback of placing the bales on their sides is that it reduced the growing area, thus requiring more straw bales per square foot. Despite these issues, for the most part we were able to use the bales for two phases and determined that bales placed on edge was preferred.

Media/top dressing. It was determined that there were no noticeable differences in germination results or plant growth between the different topdressing treatments. The top dressing chosen going forward will be based on what is most cost effective for the season. Most likely compost during the summer and bagged when compost is not available. We will use Daniels Plant Food, a natural soy based fertilizer in conjunction with Sustane. We determined that fertility using just Sustane as a side-dressing in the bell peppers was not adequate. We will supplement with Danials Plant Food, a water soluble fertilizer in every other watering for both peppers and sugar snap peas.

Environmental Conditions. The straw bales did not break down or compost enough to create any significant root zone heat for the plants. Greenhouse heat retention was improved by approximately 3 degrees F when an inner cover was used. We maintained a minimum night temperature of 40 degrees F during the winter months. Our biggest challenge however, was controlling moles and mice in the greenhouse during all season. These rodents seek shelter in the straw bales and damage a number of crops in both early and late stages of growth. We have decided that rather than fight the mice and moles we will focus on growing crop that so far have not been appealing to them. Despite not being certified, our organic approach makes the controlling of rodents very difficult.

Summer Crop- Year 1
Tomatoes had a lot of vegetative growth but not a lot of fruit. One remedy may be to pollinate the tomatoes in the greenhouse. Another issue with the tomatoes is that a taller structure is needed to accommodate the height growth of the tomato plants grown on a raised bale. We also lost a lot of tomatoes to mice and moles that seek shelter in the greenhouse and straw bales. We observed that strawberries could be a potential crop, but damage by mice and moles would have to be overcome in order to make it a viable summer crop.

Summer Crop- Year 2
Peppers were our best summer crop both in growth and in yield, averaging .5 lbs and yielding 3 lbs per linear foot of bales. We had no disease or pest pressure. The mice and moles did not bother the peppers and we were able to harvest an average of 4 peppers per plant without sun scald or blossom end rot both of which were encountered in our outdoor plantings. We learned that using water soluble Daniels Plant Food, a natural soy based fertilizer, in conjunction with Sustane as a side dressing provided the best results. We also learned that the peppers need to be well established before the severe summer heat sets in. Peppers (2 inch liner transplants) planted on June 15 faired much better than those planted on July 1. We also learned that staking was very helpful for peppers grown in bales as the looseness of the medium doesn't allow for great anchoring. A summary of our final pepper planting is represented below.

Expense Item, Number of Units, Cost /unit, Total Cost, Cost/Crop
Bales 24, $ 2.50, $ 60.00, $ 30.00
Soil (6 )2.8 cu ft bags, $ 11.00, $ 66.00, $ 49.50
Seeds 1/2 lb/1000 sds, $ 6.50, $ 3.25 $ 3.25
Fertilizer 6 lbs, $ 1.20, $ 7.20, $ 7.20
Electricity 0, $, - $, - $ -
Nat. Gas, 0, $, - $, - $ -
LED 60 diode Full Spectrum, 0, $, - $, - $ -
LED 200 diode Red Spectrum, 0, $, - $, - $ -
Labor (hrs) 8, $ 8.00, $ 64.00, $ 64.00
Total $ 153.95
Income yield in lbs
lbs. peppers harvested in summer 2011, 40, $ 2.00, $ 80.00, $ 80.00
Net Profit (Loss) $ (73.95)

This yield represents a 14 foot row of peppers that were transplanted on June 15. These peppers were harvested over a 6 week period from September 2 to October 7, consistently producing between 6 and 8 lbs per harvest. We had a frost on September 14 and 15 that probably would have damaged any remaining field planted peppers. Whereas the small number of garden planted peppers suffered from sun scald and blossom end rot, no disease damage was found on the greenhouse grown peppers. The remaining 46 feet were transplanted on July 1, but did not produce market quality peppers. The 100°F temperatures during the early part of July really set these plants back and they never fully recovered. The plants were small and the peppers they produced were also small and misshapen. If all rows had been planted in mid June and been successfully grown to harvest [we would have expected] a yield of 160 lbs and a profit of approximately $167.00 or $.75/sq. ft of greenhouse space. Going forward we will transplant peppers from 4 inch containers, by June 15 so that harvest can start 2-4 weeks earlier.

Fall/Winter Crop-Year 1. Due to either poor germination, predation, or excessively slow growth, it was determined that most of the winter crops would not be carried forward after year 1. Spinach, however was the exception. Spinach had no observed injury due to predators in the greenhouse, germinated in a close and short window, was ready to harvest in less than 60 days, and had an excellent sweet and mild flavor. The spinach also grew well without any apparent sensitivity to the amount of light in the greenhouse. We hope to interplant spinach with sugar snap peas for in our next late summer planting.

Winter/Spring Crop- Year 1 and 2. Based on our first year Phase 2 results, we chose to focus on sugar snap peas for Phase 3. As a high value crop that utilizes the vertical space in the greenhouse, does not need outside pollination, and can be grown at reasonably cool temperatures it presented us with a very appealing crop option. As such, we began a detailed research project to identify the best lighting options for sugar snap peas. The finding from this component of our project were detailed in a Masters of Agriculture in Horticulture Integrated Project. A summary of the results are included in the table below.

Expense Item, Number of Units, Cost /unit, Total Cost, Cost/Crop, Cost/Sq Ft/Crop
Bales, 24 $ 2.50 $ 60.00 $ 30.00 $ 0.13
Soil, (6 )2.8 cu ft bags, $ 11.00, $ 66.00, $ 49.50, $ 0.21
Seeds, 1/2 lb/1000 sds, $ 6.50, $ 3.25, $ 3.25, $ 0.01
Fertilizer, 6 lbs, $ 1.20, $ 7.20, $ 7.20, $ 0.03
Electricity, 468 kWh, $ 0.10, $ 49.00, $ 49.00, $ 0.20
Nat. Gas, 180 therms, $ 0.71, $ 127.80, $ 127.80, $ 0.53
LED 60 diode Full Spectrum, 8, $ 24.00, $ 192.00, $ 6.00, $ 0.03
LED 200 diode Red Spectrum, 28, $ 68.00 , $ 1,904.00, $ 60.00, $ 0.25
Labor, 16 hrs, $ 8.00, $ 128.00, $ 128.00, $ 0.53
Total $ 460.75 $ 1.91
Sugar Snap Peas Harvested-Spring 2011, 9 lbs, $ 6.00, $ 54.00, $ 54.00, $ 0.23
Net Profit (Loss) $ (406.75) $ (1.68)

Future Work/Changes Some possible changes that effect energy inputs might include: planting peas in mid-September, thereby heating and lighting on the backside of crop time, reducing heating cost, and maximizing lighting efficiency (while this timing would not provide a 'first to market' advantage, it would provide an out of season advantage); reducing the hours of lighting per day and/or increasing the coverage area by raising the initial lighting set-up; and finally, altering the minimum night time temperature to reduce heating cost or reduce the crop time.

In conjunction with the above possible changes, yields may be influenced by; taking proactive measure to limit the risk of disease, monitoring for micro nutrient deficiencies and/or by altering planting density to maximize space, especially if horizontal airflow fans (HAF) are used. Based on an average of the 4 highest yielding blocks in our second sugar snap pea planting of .5 lbs./ lf (with high disease pressure), if bales were run lengthwise and plants were not spaced to separate blocks, it is conceivable that the same greenhouse space could support 60 lf rather than 30 lf. For this layout, there would be 720 total plants and 30 total lights equaling 260 watts. In this scenario, the same space yielding .5lb/lf, could have yielded a total of 30 lbs. of edible pea pods. At $6.00/lb, a loss of $114 would have occurred.

Table 2 reflects hypothetical expenses based on Dec. 5, 2011 LED cost per light, a 2 ft light spacing, a 70-day growing period requiring approximately 30 days of supplemental light and heat, 10 hours of supplemental lighting, 60 lf of planting and .5 lb/lf yield. These alterations reduce the heating and lighting inputs to just over one third of total expenses. If disease pressure was managed and yields of .2lb/plant (a typical amount for field grown sugar snap peas) were achieved, a yield of 144 lbs and a profit of $570.00 could be realized. While strictly speculative, it is believed that these scenarios do offer enough incentive to warrant additional cropping attempts.

Expense Item, Number of Units, Cost / unit, Total Cost, Cost Per Crop, Cost/Sq Ft/Crop
Bales 24 $ 2.50 $ 60.00 $ 30.00 $ 0.13
Seeds, 1/2 lb/1000 sds, $ 6.50, $ 4.87, $ 4.87, $ 0.02
Soil + Compost, (6 )2.8 cu ft bags, $ 11.00, $ 66.00, $ 33.00, $ 0.14
Fertilizer, 6 lbs, $ 1.20, $ 7.20, $ 7.20, $ 0.03
Electricity, 116 kWh, $ 0.10, $ 12.06, $ 12.06, $ 0.05
Nat. Gas, 80 therms, $ 0.71, $ 56.80, $ 56.80, $ 0.24
LED 90 diode Full Spectrum-2011, 10, $ 20.00, $ 200.00, $ 6.25, $ 0.03
LED 200 diode Red Spectrum-2011, 20, $ 54.00, $ 1,080.00, $ 33.75, $ 0.14
Labor, 14 hrs, $ 8.00, $ 112.00, $ 112.00, $ 0.47
Total $ 295.93 $ 1.24
Sugar Snap Peas Harvested-Scenario #1, .5lb/ft =30lbs, $ 6.00, $ 180.00, $ 180.00, $ 0.75
Net Profit /Loss $ (114.31) $ (0.49)
Sugar Snap Peas Harvested-Scenario #2, .2lb/plant=144 lbs, $ 6.00, $ 864.00, $ 864.99, $3.60
Net Profit /Loss $570.68 $2.36

Table 2. Hypothetical Expense Report- Fall Grown Sugar Snap Peas 2012- 224 sq. ft Greenhouse space

We replaced out small greenhouse this past fall and were not able to plant sugar snap peas in the fall season. We have however, doubled our LED lighting and will use what we learned from the previous two years to begin a pepper-pea rotation this year. Peppers have been seeded and will be transplanted on June 15 from 4 inch containers rather than 2 inch liners. We plan to follow with peas by September 15th. We hope the fall planting will allow for harvest to be completed by Dec. 1.

One of the most important things we learned from this project was that if the scale of the production isn't big enough to produce a meaningful income, then it isn't worth the management time to carry it forward unless a passion for the product is an underlying factor.

Even though we are a small operation that relies on diversity and multiple income streams, the opportunity cost of our time to manage an enterprise isn't just measured in hours of labor. If we can't reasonably scale something to produce a profit in the thousands of dollars rather than hundreds of dollars there has to be a real passion for the product.

We will in all likelihood approach the use of straw-bales in a different way. As we grow our hog operation and have straw from winter deep bedding, the production of compost has taken on a larger scale. The seasonal timing of straw removal from our hog hoop building may offer the opportunity to "hold" the straw for the late spring thru fall in a greenhouse setup for the production of peppers and sugar snap peas. I have designed a greenhouse bench that would serve as framing to hold the composting straw bedding pack. This would save the cost of bales for growing and would still produce compost after growing to apply in our orchard.

We also learned that in a typical winter, like the one we had in 2010-2011, the cost of heating the greenhouse mid-December thru mid-February makes producing a profitable crop difficult. Because we have an established use for the greenhouse in spring, we could not justify the risk involved to try to produce a winter crop that would potentially have a low yield, or a high cost due to heating requirements. We do, however, feel that the additional 2 seasons of greenhouse use is a worthwhile use of this resource.

The use of straw-bales as a growing medium has pros and cons. On the positive side, they do allow flexibility, they offer a raised bed that makes many growing tasks easier, weeding is minimal and when required, easier than in the ground weeding and they can be recycled. The main negative features were the difficulty in moving them once used and the habitat that they created for moles. Because we used a greenhouse that had polycarbonate end wall and a 36 inch door, we had to move the bales manually. We put up a larger open ended greenhouse this past fall that will allow for tractor access and a much easier means to move straw in and out. To solve the mole and mice issue, we will focus on two crops that seem to not be of interest to moles and mice.

The use of LED lighting also had its pros and cons. Stringing the lights in an economical manner was labor intensive. Because LEDs have a narrow lighting arc and low light output per bulb, they have to be positioned close to the plant canopy. This required adjustments both between crops and during crop production. We hope to limit this issue with sugar snap peas by growing them in the fall when their lighting requirements will increase as the plant grows thus lessening the need for lighting until the plants have reached a height where the lighting can be hung in a fixed location. Also the cost of LEDs has come down over 20 percent since we purchased them, making their use more economically viable. If costs continue to come down, utilizing them for season extension will become much more viable. As our research established, they are effective as a grow light.

We also learned that it is difficult to grow specific high value crops in a window that allows multiple seasons of use. If we can get peppers grown and harvested by September 10 and get pea seedlings in by September 15th, we might be able to manage both of these crops successfully. We could conceivably be "first to market" with peppers sold direct from the farm as apples begin to come in, while selling peas to co-ops during an "out of season" timeframe there by getting a premium price.

In the spring of 2011, I gave an in-house field trip presentation to St. Ambrose ECEC in
Woodbury. We had 3 separate sessions with about 40 students attending each session. The focus was on edible pea pods and making the connection from seed to plant to pod. The kids all snacked on freshly harvested pea pods and did a pea-germination experiment in their classrooms.

In December of 2011, I presented much of the what I learned from this project through a Masters of Agriculture in Horticulture Integrated Project presentation. There were approximately 40 students and faculty from the University of Minnesota in attendance.


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.