In The Beginning...

This installment marks the beginning on what is intended to be a continuing observation and analysis involving the production of winter greenhouse crops using biological processing methods while enlisting modern horticultural analytical tests and methods.

The project is relatively small scale in nature, as it is confined to a backyard greenhouse measuring 3 meters X 3.6 meters X 2.25 meters of vertical height to the ridge. The greenhouse is a gothic steel arch coldframe covered with single four year poly ( Tuff Lite). One of the sidewalls rolls up manually to 1.5 meters above grade for summer venting and hardening off plants (“cold treatment”). The single poly (6 mil, four year) provides relatively high light transmission, and as a single sheet covering it provides a very airtight seal retaining heat. It also helps to diffuse light, noted to produce healthier crops. Regular vapor barrier is not very well suited as a greenhouse covering, although may suffice if a few months use is all that will be required. There are many types of greenhouse poly films available including anti-condensate formulations and infra-red reflecting to reduce heat loss.

The poly used will last at least four years as it was installed correctly. Polylock simplifies installation and helps to strengthen the structure. Preferably, the poly is installed during warmer weather as it stretches. When it cools to more average temperatures, it contracts like a skin tightening around the structure. Double layers of poly (6 mil) can be inflated with outside air via a small blower fan (45cfm). This airspace provides a very high degree of insulation and acts as a cushion to winds, etc. However, the double layers cut down light transmission. In South-West British Columbia we are blessed with very moderate winter temperatures, but receive very little in the way of strong light intensity during winter months. So, single ploy is a good choice. Although the poly is usually a little bit more advanced each time you re-install it, it is a continuing expense and chore. Single poly properly installed can look as clean and clear as glass, without all the cracks. Next fall the installation of a rigid polycarbonate covering will be explored.

The goal of the experiment is to determine the economic feasibility of producing mixed greens (Mesclun Mix) using a “living system”. The living system itself (for lack of a better name at the moment) is also an experiment. The greens are to be produced in a series of raised beds filled with an organically certifiable soilless mix and fed with an aerobic compost tea extracted in a biological reactor located in the greenhouse. The greenhouse will require moderate additions of heat to maintain acceptable ambient temperatures for the production of baby greens (15 to 24°C). A propane fired carbon dioxide generator controlled via hydronic thermostat will double as the heat source and as a catalyst to production to offset relatively lower light levels and duration during winter months. A 10” axial fan will provide winter cooling and air exchange as humidity rises as occasionally do temperatures. It is activated on rise via thermostatic control. A relatively inexpensive and ingenious device allows a transmitter to be placed inside the greenhouse while the temperature and humidity can be monitored from a remote unit. The device also has a programmable alarm so the operator is alerted if a preset temperature is exceeded or not met (i.e. out of heating fuel).

A large black polyethylene 300L+ reservoir is kept inside the greenhouse during winter months and will be moved outside during warmer months to free up valuable growing space. It is hypothesized that it is worth the loss in growing space during winter as the large volume of water will act as a heat sink thus help to radiate heat back to the crop collected passively. Also heating the reservoir without an insulted structure could prove to be very costly, even in a mild BC winter. The reservoir feeds three growing beds containing the organic soilless mix. Two of the beds measure 0.4 M X 3.6 M, while the central bed measures 0.8M X 3.3 M. However as indicated there is some sacrifice (0.4 M square) to growing space in winter months for a cozy reservoir, so the central bed only offers 0.8 M X 2 M. This gives us about 4.5 square meters of growing space. The floor space efficiency would go up relatively higher given the same arrangement on a longer greenhouse. The two aisle ways are about 0.4M wide running down the length on either side of the greenhouse. There is some room here for additional trays or containerized plants if required, but it is preferred to keep the aisle ways free from obstructions, particularly in a research setting.

A series of ½” PVC rigid pipe acts as a manifold to deliver water and organic solutions from the reservoirs injecting it beneath the surface of the soilless mix. There is a small hole drilled (about 4mm) about every 12 to 15 cm down the length of the manifold which runs from one end of the beds to the other in a parallel series spaced about 12 cm apart.

Organic compost tea extracts are brewed and added to the reservoir at levels and frequencies to be determined by experimentation and analysis of the soilless media and the organic tea solution. Readings can be compared to “optimal” input requirements for greenhouse lettuce production. However, these values will act only as a guide line as we are attempting to produce baby lettuce which will mature in 28 days or less, and organically to boot. It is also hoped that the elevated carbon dioxide levels will speed production and increase harvest levels.

The beds and soilless mix were prepared well in advance of the intended planting date (ideally at least a month), so that there was an opportunity for the biological processes associated with composting and the release and conversion of nutrients from organic materials added and used for extraction. After all, Rome wasn’t built in a day. The beds were constructed from un-treated 2” X 12” lumber and reinforced with steel corner brackets and wood lathing to prevent buckling and excessive distortion of the wood under warm and moist conditions. The soilless mix was prepared directly in each of the beds using the following materials in the following proportions. All amendments were OMRI certified organic, and note that the mix could also likely be certified as Vegan-organic. After all it’s maybe not such a bad idea to stay away from decomposing animal by-products such as bone and blood. Note that many commercially prepared soilless mixes are not certifiably organic, the wetting agents they contain are often the first strike against them.

Once well blended, the mixture was watered as needed to maintain even moisture. Although this may initially seem a little odd as there no plants involved yet, it allows time for the microbial process to begin digesting the organic materials added to become readily available and as stored nutrients that will be required to fuel plant growth. About 10 days prior to the initial planting/seeding date, the process of the organic tea extraction began, as it was determined through moderate research that a brew/extraction time of four to five days was considered optimal. Several days should also be allowed to pass after the initial application of the biological brew to the growing beds to allow sufficient time for the organic compounds to be taken up into the biological matrix. A strong understanding of processes such as the Nitrogen Cycle is invaluable when supplying nutrients in biological form.

The tea extract was brewed in a homemade reactor constructed of black 20L food grade pails with lids. The design was from a culmination of articles and studies found on the internet. Although significantly modified, most of the influence for the construction of the apparatus was gained from a study performed by Richard Merrill et al at Cabrillo Community College, Soquel California and published in the Organic Research Foundation Journal (Winter 2001, Number 9).

ATTRA ( Appropriate Technology Transfer for Rural Areas) also offers a wide range of informative online journals including “Notes on Compost Teas: A Supplement to the ATTRA publication-Compost Teas for Plant Disease Control” by Steve Diver (March 2002).

The extractor apparatus is located in the greenhouse, occupying mostly vertical space. The ambient temperature of the greenhouse was maintained above 16°C constantly and rose to as high as 40°C during peak hot spells. A poly bag with a fine meshed bottom used for extraction of plant materials the following organic materials were measured and combined. The filter bag was suspended in the upper chamber of the reactor. From a well aerated fish pond, about 25L of water was gradually added to the reactor. The lower chamber pumps the solution up and through the filter bag, were it passes through an aerated bio filter before returning again to the lower chamber. It was intended to operate continuously, but was not practical as the bag did not drain fast enough, no matter what the flow rate. As a result, the solution was cycled from the lower chamber to the upper chamber intermittently. This may also allow for a more complex range of microbes as the organic materials used for extraction do not remain completely submersed at all times. The tea was brewed for five days.

The following batch of tea was modified slightly. Primarily the organic materials for extraction were placed in a fine poly mesh zippered bag. The entire bag was “filter” material instead of just the bottom, so the solution could flow freely through the material and aerated biological filter before returning back to the lower chamber. The cycle is timed with 15 minutes “On” and 15 minutes “Off” for 24 hours per day during the four to five day extraction period. The second batch of tea also had slightly higher additions of fine, dark earth worm castings.

The biological tea will supply the crop with some soluble plant nutrients and continue to add organic matter and beneficial activity throughout the cropping cycle. Based on some experimentation teas will be blended to supplement nutrient levels in the raised beds as indicated by periodic analysis of the growing media. Ideally, we would like to determine soil N (nitrogen as NH4, and NO3), P (phosphorous as elemental and phosphate PO4), K (potassium), Ca (calcium), Mg (magnesium), and Fe (iron). We would also like to measure those elements and their relative proportions in the biological tea preparations so that we may adjust levels accordingly. As the media and brew is experimental more frequent testing is required as all variables are relatively unknown. Using a commercially prepared tea with certified levels of nutrients may be more practical for commercial applications although periodic analysis of the growing media is still recommended for more decisive application rates and intervals. The relative acidity (pH) of both the media and tea solution will require testing to make necessary adjustments for maintaining optimal levels for healthy biological activity. Professional laboratory analysis of the tea extracts and growing media will be performed by Grotek (Langley, B.C.).

About 20 days after the beds were mixed and initially wetted, the first sample(s) of the media were taken from a depth of 7cm and 20cm. In the first sterile mason jar, a small portion was taken at a depth of 7cm from each of the three beds for a total volume of about 500ml. In the second sterile mason jar, a small portion was taken at a depth of 20cm from each of the three beds for a total volume of about 500ml. The samples were immediately frozen after the jars were sealed to prevent changes in nutrient levels which will occur as temperatures and other variables change. We want a sort of frozen picture in time in terms of the soil’s life. A 500ml sample of the organic tea was collected into a sterile mason jar and also frozen after completion of the extraction process and at the time of placement into the reservoir.

After four days of brewing 12L of very fine (and odiferous) tea was pumped from the lower chamber into the reservoir, containing 100L of fresh water (TDS >30 ppm, pH 7.3). It was allowed to aerate for eight hours via air pump in reservoir prior to application. The temperature of the solution was near 20°C, the pH was 6.2 without any further additions. The solution was free of debris before entering the system, and an inline filter before the injection manifolds helps to prevent blockage of irrigation orifices. With a ½ H.P. pump the solution was emptied from the reservoir in less than two minutes. This appeared to achieve deep penetration into the growing media while providing a high level of aeration and promoting even moisture levels in the substrate. Four days after the tea solution had been applied, and another (modified as discussed) batch of tea had commenced brewing soil samples were retaken with previous methods and at previous depths, also kept frozen to the time of delivery to Grotek analytical services.

In the next installment we will have received our laboratory results and should have begun to formulate and apply a crop nutrition management plan. At present we are awaiting the arrival of our commercial mesclun seed mix and a few special varieties that may help to tailor a blend of our own. Note that greens produce better under slightly cooler conditions, so seeding will not occur until mid to late September.