Begin the season with a clean, weed-free and disinfected greenhouse. This means clearing the growing area of any plant debris, weeds, and any discarded flats or tools. After clean-up, wash and disinfect empty benches, potting areas, storage shelves, tools, and leftover cell packs and flats that you plan to reuse.
It is important to note that chlorine bleach is an effective sanitizer, but there will be a 50% reduction in strength of a chlorine solution after just two hours. Therefore, you should prepare a new solution each time you plan to sanitize.
Once you have the growing area and equipment sanitized, be sure to avoid recontamination. Dirty hose nozzles or tools can contaminate potting soil and the general growing area. Be sure that everything brought into the sanitized area is also clean. The floor or soil in the growing area is a good source of insects and diseases. Do not stand on the benches after they have been cleaned, as you can easily move diseases up from the floor with your shoes. Use hooks to keep your hose nozzle off the floor.
Ideally, grow your transplants off the floor as well, either on benches or pallets. The floor in your greenhouse should be well drained and cleaned before plants are started there. Some growers have taken to covering the entire floor with black fiber cloth to both prevent weed growth and make clean up easier after transplant production. Once dry, plant and soil residues are easily swept-up and removed.
Does your growing area have good air movement? Circulating air not only distributes heat more evenly but can also reduce condensation in the greenhouse. Consider installing a horizontal airflow (HAF) system in your transplant production area.
I’ve heard growers ask if allowing the greenhouse to ‘freeze’ for several days in cold weather means that insect pests will be killed; and the answer is no. Heat can be more effective than freezing for pest destruction. For example, heat has been shown to be more effective for the control of thrips, according to Leanne Pundt of the University of Connecticut.
In one study, high temperature (104ºF) combined with very low humidity (less than 10%) for three to four days killed most adult thrips. However, your greenhouse must be completely weed-free for this method to work. If you have constant thrips problems, this control method might be something to try this summer.
Finally, always use disease-free media for transplant production. If using soil, be sure it is pasteurized before you bring it into the growing area. Successful soil pasteurization requires 30 minutes at 180ºF. Be sure to frequently sanitize and maintain clean areas where soil is mixed and pots are filled.
If you are producing both vegetable transplants and ornamentals, I strongly recommend that you have separate growing areas for each group of plants. Bringing cuttings of flowering plants into the vegetable area can introduce pests, such as thrips, and diseases, such as tobacco spotted wilt virus (TSWV). Look at your available space(s) and plan accordingly.
Take some time to prepare your vegetable transplant greenhouse now to reduce disease and insect problems later this season. Waiting until seeding time to start this chore may not leave enough time to do the job thoroughly. This could result in a great deal of time and money spent later to control a disease or insect infestation that could have been prevented.
This article appeared in the January 2014 Vegetable and Small Fruit Gazette, the Penn State Extension newsletter for vegetable and small fruit growers.