The problem this project was designed to address was: how early warm season vegetables can be produced to extend the growing season on the front-end by using low energy input, a greenhouse and other season extension techniques to offer produce for higher-value specifically to the early season market. We planned to convert an existing ornamentals coldframe to an inflated double layered hoophouse with additional internal row covers with a targeted transplant date in early April 2009.
Our farm is at 3,000 feet in the northwest mountains of NC where we have recorded a frost every month of the year except August. Our average frost free growing period is from May 15 thru September 27 giving us a narrow window for growing warm season crops.
Our local Farmers’ Market allows only produce and plants grown in our county to be sold at the Market. The existing produce growers all hit the Market with the same staple produce at the same time. This keeps prices down due to large quantities of the same staple vegetables. We want to offer our vegetables earlier so we do not contribute to the glut and price reduction and we want to support the market by enticing customers earlier in the season with a broad variety of quality fresh produce. Also by offering traditionally later season produce earlier we will be able to realize a premium price and support the sustainability of our farm.
Warm-season produce generally does not appear at our market until late-July and is not available in large quantities until August due to our colder climate. This leaves our Market customers waiting and drooling for most of the summer for their first ripe tomato!
With this project we hoped to learn the best methods for protecting tender plants from cold and freezing without supplemental heating so we can offer this to our produce mix by late June.
This project used an existing greenhouse that had been used to over-winter ornamental plants. It was covered with 1 layer of white one season poly (plastic). We replaced this with 2 layers of clear, non-drip greenhouse plastic one of which was an infra-red retentive poly. The 2 layers were separated by a layer of air circulated by an inflation blower. Irrigation was provided with drip tubes with 18″ spacing with emmiters rated at 1GPH. The greenhouse had 3 growing beds in it: 2- 3’x 95’ and one 7’x 85’ with 1.5’ aisles. The beds were covered with low-tunnels for the test, either agribon+ 30 or clear 6 mil. plastic to provide an additional level of freeze/ frost protection. Other plants were protected with only a wall-o-water. The soil surface was covered with IR retentive plastic or woven black fabric. We placed maximum/minimum thermometers and soil thermometers under each type of protection for each type of vegetable planted. We recorded both inside and outside temperatures daily. This data was collected until the plants outgrew their protection. We were able to collect the data for 4 weeks, from early May through early June. We planted 1 variety each of tomato (88 plants total for two varieties), pepper and eggplant (44 plants each) so there were enough plants for the test repetitions.
The test involved 11 plants of each vegetable under each type of protection plus 11 control plants of each. Though the control plants were not expected to survive they did so we did not have to replant that area with greens as we had expected. We measured the growth of select plants weekly, recorded when they flowered, set fruit and when the fruit ripened. We kept track of when we had the first saleable fruit and how much weight we sold from the plants in the study during the growing season. This was done for each type of protection and vegetable type involved in the study.
The plants were grown under their respective covers with the planned addition of a very heavy spun-bonded fabric we already had on site which would have been used to cover the rows if the nights got extremely cold. This added layer was not needed in 2009.
We amended the soil as indicated by a soil test and planted a cover crop of annual rye for November through February 2009 to prepare for 2010 crop. We talked with a nearby worm farmer about using worms to aerate the soil in our greenhouse. He said we should be able to keep the worms in the greenhouse beds so we began a worm population by adding 2 pounds of worms per bed.
The plan for this greenhouse also included planting a vegetative farmscape border down one side to attract beneficial insects and offer “trap” alternative plants for insect pests. Because of our existing ornamental and cut flower operation, this farmscaping was deemed unnecessary.
All of the transplants for this project were produced on site in our heated greenhouse. They were ready to transplant into the test greenhouse by early April.
The bed space in the greenhouse not planted in plants for the research were planted in lettuce, spinach, endive, and mache for the early market. These vegetables proved to be excellent sellers for us last season.
Conversion of the target greenhouse began in February 2009 with the sale and transfer of the existing ornamentals inventory. This was followed by removal of existing ground fabric and removal of approximately 30 cu. yards of gravel to the bare soil level. An equipment breakdown with delay for parts replacement led to completion of the transformation at the end of April. Soil Amendment, installation of drip irrigation, and laying of bed covers was completed in late April. Transplanting into the converted structure and covering with the double poly layers and row covers was completed in early May.
Meanwhile, seed was sown from Feb. 15 thru mid March in flats placed on soil heat mats in a screened seed box in our “heated” greenhouse with the greenhouse air temperature maintained at no lower than 34 degrees F. The seed box was held at 68 degrees with the heat mats and nighttime reflective tekfoil and agribon covers. Seedlings were moved to 2 1/4” x 3” pots from March 1 thru April 3 and grown on with air temperatures at 50 degrees minimum until transplanting into the hoophouse. Most of the transplants were ready by April 10th but waited for completion of the greenhouse conversion.
All transplanting to the hoophouse was completed by May 5th and double poly, row covers, wall-o-waters, and recording thermometers were in place by May 11th. Daily temperatures were recorded, periodic plant measurements were taken, and date of flower set, fruit set, and harvest data were taken. Because temperatures were high enough in the hoophouse and some plants had outgrown their row covers or wall-o-waters all inner covers were removed by June 5th. Data collection continued thru Oct 18 with only outside temps, inside air temps, and inside soil temps collected after June 6th. Flowering dates, fruit set, and harvest data also were recorded thru Oct 18th.
The test data revealed that a combination of agribon+ 30 row covers with inflated double poy hoophouse covers utilizing an IR retentive inside plastic layer provided the best protection during the period of coldest outside temperatures. Daytime high temperatures in the hoophouse began to reach and exceed 100 degrees F during the first two weeks in June requiring opening the plastic endwalls to the full height of the hoophouse and raising the sidewall plastic layer 3-4 ft. to ventilate the house and maintain lower temperatures. Sidewall and endwall covers were raised and lowered manually as needed to maintain higher nighttime lows. After June 6th row cover protection became unnecessary and in some cases kept temperatures too high around the plants. We applied these findings to our growing methods in 2010. After an April 6th initial transplant date into the hoophouse in 2010 Agribon AG-70 row covers were utilized for temperature management inside the hoophouse around the plants. We successfully held low temperatures under the row covers to 37 degrees or higher even when the outside lows reached the low 20’s. As a consequence of earlier planting and improved temperature management we harvested an earlier crop in of tomatoes on June 11, 2010, 1 ½ months ahead of the beginning of tomato harvest for conventional outside growing techniques.
One of the lessons learned in this 2009 study was the need for better temperature monitoring equipment. The inexpensive Taylor maximum- minimum thermometers we requested for this project suffered from repeated failure due to the fluid escaping around and above the recording indicators making that day’s data unuseable. A preferred alternative would be to use recording digital data monitors for all air temperature and soil temperature data. An additional data element we should have tracked would have been outside soil temperatures to highlight any soil temperature gains from using the hoophouse and row covers.
In 2010 we added tests for five additional determinate or semi-determinate tomato varieties. The five new varieties were Orange Blossom, Carolina Gold, Green Zebra, Legend, and Cold Set. All of these varieties performed well under the row covers except Cold Set which had limited growth and yields. Orange Blossom proved to be the earliest producer after identical initial transplant dates.
Educational & Outreach Activities
As indicated above the targeted data collection and analysis was completed for this project in 2009 and was applied to our methods and procedures this season (2010) with successful introduction of early warm season produce to our market by mid to late June. We were able to eliminate the row cover protection methods that did not work in 2009 and continue the test while adding determinate type tomatoes to the mix. The combination of double layered hoophouses with agribon+ 30 row covers kept our air temperatures around the plants above 37 degrees F and raised soil temperature levels under the row covers earlier than our outside unprotected soils. An added benefit from our 2009 harvest data confirmed earlier Cornell research that Prudens purple yielded more pounds of harvestable fruit than Cherokee purple in our heirloom trial even though the Cherokee purple plants began to produce earlier. Eggplant and Pepper harvests were also almost one month earlier with the first eggplant harvest on June 18th and the first pepper harvest on July 10th. The bulk of the harvest for these crops occurred during the period traditional for these crops in our area during August – September.
We did not plant as extensive a farmscape as we had originally planned because many of those plants already existed along the side of the test structure. We have a cut flower and ornamental nursery operation that complemented the farmscaping plan.
We also did not need to introduce beneficial insects into the hoophouse because many of them were already present. They would have been helpful late in the season when aphids and whiteflies briefly infested our tomato plants. One application of organic controls cleaned up that problem.
Another earlier observation we had made concerning late blight control was proved with this hoophouse. Even though we had extremely high amounts and frequency of precipitation ( over 32 inches of rain May – September ) we had no evidence of late blight in our hoophouse tomato crop. Our outside tomato crop was completely decimated in late August by that same rainfall and subsequent late blight even though we followed a regimen of Oxidate, Serenade, and copper sprays. The hoophouse cover and controlled drip irrigation controlled the moisture levels on the tomato leaf surfaces as well as soil splash on the stems. This reduced conditions conducive to late blight and kept us from using any protective or curative sprays in the hoophouse. (Rainfall totals by month were: May 9.27 in., June 5.46 in., July 3.26 in., Aug. 6.91 in., Sept 7.42 in.)
Other growers, particularly Steve Moore of the NC Center for Environment Farming Systems (CEFS), had warned us of the problem of poor phosphorus uptake in plants under cold conditions. We too observed these conditions in our early tomato crop and corrected with a watered in application of bone meal. The plants improved as temperatures warmed.
In our area 8 farms received NRCS grants to install hoophouses on their farms. One additional farm constructed a moveable hoophouse at their own expense. Of those farmers four farms have adopted some of the same techniques used in this project. The NRCS hoophouses only paid for a single layer of plastic on those houses, but at least one farmer is considering adding a second layer based on data from our project. We have also shared data from our project on a national webinar on hoophouse culture as well as through extension meetings and local ag. agents. We have provided advice to other growers on organic fertilizer blends we developed in growing our transplants, on pruning and trellising techniques, and on variety trials for tomatoes, peppers, and eggplants. On August 4, 2009 we hosted a field day on our farm to tour the project and summarize our results at that point. We are developing a handout to concisely present the results from our project.
Further monitoring projects like this one should absolutely consider better monitoring instruments, particularly temperature data loggers. We would like to see further studies of the benefits of soil covering plastic mulches particularly the new IR retentive mulches. Other valuable research might address better ventilation control methods during the warmer periods of the growing season. Drip irrigation and fertigation techniques would be another valuable area for more information.