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.
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 greenouse environment needs to be regularly cleaned and disinfected to reduce potential for diseases such as damping-off, crown and root rots. Weeds need to be removed to reduce the potential overwintering sites for many different insect pests. While the greenhouses are empty, between crop cycles, is an ideal time to clean and disinfect your greenhouses. 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, removing organic matter and mineral deposits without scrubbing. Apply with a foamer and allow to sit for 5 minutes before rinsing with a high-powered hose.
After the surfaces are thoroughly cleaned, you can then use a disinfectant. There are many commerically available disinfectants developed for greenhouse use. Each product has a specific range of activity on different types of surfaces (wooden benches are more difficult to clean than wire mesh benches). 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 2.0OG, Jet-AgOG, SanidateOG and PERPose PlusOG. All 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. It's half life, (the time required for a 50% reduction in strength of a chlorine solution) is only two 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.
Alcohol (70%) can be used to sanitize knives or cutting tools.
Clean and disinfect irrigation systems.
Avoid using Unvented Heaters in Greenhouses
One of the most critical features in greenhouses 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. Levels as low as 0.5 parts per million (ppm) can cause injury to some plants. Once the sulfur dioxide enters the plant through the stomates, it reacts with water to produce sulfuric acid that causes leaf burn, flecking and general chlorosis. Tomatoes and white petunias are very sensitive and will show damage in as little as one 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 temperatues are cold so there is more demand for heat and double poly greenhouses or hoophouses are tightly sealed.
Greenhouse Management Transplant Production Resources
Aldrich, R. and Bartok, J. Greenhouse Engineering, https://ecommons.cornell.edu/bitstream/handle/1813/69429/NRAES-033.pdf?sequence=1
Bartok, J. Greenhouses for Homeowners and Gardeners: PALS Publishing (Formerly NRAES), https://ecommons.cornell.edu/handle/1813/69450
Most recent version, New England Greenhouse Floriculture Guide: A Management Guide for Insects, Diseases, Weeds and Growth Regulators, available from: https://greenhouseguide.cahnr.uconn.edu/
University of Massachusetts Extension Greenhouse Crops and Floriculture Program: https://ag.umass.edu/greenhouse-floriculture
University of Conn Extension Greenhouse IPM Program: https://ipm.cahnr.uconn.edu/greenhouse/