Greenhouses

Vegetable transplants are commonly grown in New England in greenhouses for field transplanting or spring sales at farm market stands. Many vegetable crops are grown from transplants in New England due to the late spring, short growing season, and desire to obtain mature, harvestable crops as soon as possible. There are many types of greenhouses, including glasshouses, high tunnels, and poly-covered greenhouses. The benefits of each greenhouse style depend on the size of the operation and goals. Large greenhouse operations typically produce under glass, while smaller greenhouses for local markets produce in simple hoop houses. 

Transplant production is a specialized part of vegetable production that requires a protected environment such as a greenhouse and careful attention to detail. Although vegetable transplants may only be in the greenhouse for a short period of time, it is important to produce high quality pest-free transplants. Scheduling, plant nutrition, greenhouse management, and pest management influence quality. Some vegetable producers choose to purchase transplants while others grow their own.

Cleaning and Disinfecting the Greenhouse 

The protected greenhouse environment needs to be regularly cleaned and disinfected to reduce potential for diseases such as damping-off and crown and root rots. Weeds need to be removed to reduce the potential overwintering sites for many different insect pests. An ideal time to clean and disinfect your greenhouses is while the greenhouses are empty between crop cycles. Remove all weeds, plant debris, spilled potting media, and organic debris. Thoroughly sweep, and then scrub or power wash to remove all organic crop debris off greenhouse floors, benches, and walls. Follow this with a high-pressure water cleaning. 

Many growers use specific greenhouse cleaners, such as Strip It Pro, which is a blend of acids, surfactants, and wetting agents that can be applied with a foaming attachment, CleanGro, or GreenShield. There are many other cleaners that remove organic matter and mineral deposits without scrubbing. These can be applied with with a foamer, allowed to sit for 5 minutes, before rinsing with a high-pressure hose. After the surfaces are thoroughly cleaned, you can then use a disinfectant. There are many commercially available disinfectants available for greenhouse use. Each product has a specific range of activity on different types of surfaces (e.g., wooden benches are more difficult to clean than wire mesh benches). Many disinfectants kill fungi, bacteria, and viruses, however, bacteria tend to be the most persistent even with treatment. Follow all label safety precautions including recommended rates, use of personal protective equipment (PPE), and plant safety precautions. Some of the products commercially available include Q salts such as KleenGrow; hydrogen peroxide products such as ZeroTol 2.0, Jet-Ag, and Sanidate are strong oxidizing agents. 

Use chlorine bleach with caution, as it is highly volatile, and can irritate skin and eyes. It should only be used in a well-ventilated area. Mix fresh solutions just before use. Its half life (the time required for a 50% reduction in strength) is only 2 hours. Chlorine is also corrosive. Repeated use may be harmful to plastics or metals. Chlorine bleach is also phytotoxic to some plants. Walks, benches, and plant containers can be treated in nurseries. 

Containers to be re-used should be washed thoroughly to remove media particles and plant debris before being treated with a disinfectant. The smaller the container, the harder it is to effectively remove debris. Smaller plug trays are much more difficult to clean than larger containers. Plant trays should also be thoroughly cleaned and disinfected. 

Heating in Greenhouses 

One of the most critical features in a greenhouse is a source of heat to provide appropriate temperatures. A frequent question by growers is regarding the use of supplemental heaters in the early spring. Do not use unvented heaters when growing transplants in the greenhouse or high tunnel. An unvented heater is one that is designed without a flue connection so that the heat and products of combustion are exhausted into the greenhouse. Unvented heaters can be fired with natural gas, propane, or kerosene, which all contain traces of sulfur. During combustion, sulfur in the fuel is combined with oxygen to form sulfur dioxide. Sulfur dioxide levels as low as 0.5 parts per million (ppm) can cause injury to some plants causing leaf burn, flecking, and general chlorosis. Tomatoes and petunias are very sensitive and will show damage in as little as 1 hour. 

Ethylene gas is another pollutant formed during combustion. Ethylene levels as low as 0.01 ppm can cause damage, including malformed leaves, epinasty (downward bending of leaves), and flower senescence. Tomatoes are a good indicator plant for ethylene because they develop downward bending of the leaves when exposed. Some growers place tomato plants in each greenhouse when they begin heating in the winter. Problems are more common when the outdoor temperatures are cold so there is more demand for heat and double poly greenhouses or hoop-houses are tightly sealed.

Heaters should be installed by a professional to ensure they are functioning properly. Many heaters and fuel types are available and growers decide on the heat source based on cost and availability. Heaters use a range of technologies and having an up-to-date heater can save on fuel costs and reduce energy. 

Greenhouse Management Transplant Production Resources

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New England Vegetable Management Guide