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If you grow your own veggie transplants, it's a simple matter to grow extras for sale at farmers markets and farm stands. Customers will be pleased to see unusual varieties not available from the big-box stores, especially those recommended by a local farmer.

Transplants for sale should be handled slightly differently than those for the field. They should be larger than those you would transplant outside, and grown in individual pots or cell packs. As a result, transplants for sale will require more time in the greenhouse, larger cells, and sufficient fertility to keep them thriving.

Large plants such as tomatoes and peppers are commonly grown in 3" or 4" pots. Some growers find that plants that don't sell at that size can be potted up into larger containers as big as a gallon pot and sold later in the season when they are flowering and fruiting. Small plants such as lettuce and leafy herbs can be grown in four-cell or six-cell packs.

Because of the growing popularity of organics with backyard gardeners, it may be wise to grow transplants according to organic standards, whether or not you're certified organic. That includes using growing medium and fertilizers that are approved for organic use. Johnny's 512 mix is a custom-blended mixture of peat, perlite, and compost that is designed to carry seedlings through to transplant size. If you prefer to mix your own potting medium, recipes are available at the ATTRA website. Eliot Coleman's book The New Organic Grower also provides valuable advice on making your own.

Research at the University of Kentucky showed that fish emulsion can be used to fertilize organic tomato and pepper transplants. In fact, transplants fertilized with fish emulsion were much bigger and healthier than those grown in a soilless mix amended with composted manure or worm compost.

The goal of transplant production should be healthy, rapidly growing plants. Here are the most common factors that cause plant growth to be checked, according to the Ball RedBook. Be sure they don't occur in your greenhouse, and you'll have a profitable crop of transplants to sell in spring.

  1. Poor physical condition of soil. The growing medium must be loose and porous to provide adequate drainage and oxygen to roots. Potting mixes with small particle size tend to get tight and hard.
  2. Seedlings must be transplanted before they get root-bound; in most cases, that's when they have their first pair of true leaves.
  3. Too low or too high nutrient levels. Follow the label instructions for fertilizing transplants.
  4. Diseases. Root rots and viruses can go undetected until it's too late if you're not watching for growth slowdown.
  5. Insects. Aphids, spider mites, whiteflies, and fungus gnats are common greenhouse pests that should be monitored.
  6. Lack of water. Transplants must be watered thoroughly and frequently. Water properly, as this tends to be one of the most common greenhouse errors.
  7. Too cold. The ideal temperature depends on the crop, but remember that unnecessarily low temperatures will check plant growth.
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Reprinted from JSS Advantage February 2011