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Vegetable Production - Transplant Production Approaches

Growers use transplants to grow long-season crops in short-season areas, improve land use efficiency, save costs when growing expensive hybrid seeds, and get early production for early markets. Using transplants can improve water savings, manage early weed problems more efficiently, ensure more uniform production, and assure better stands.

High quality transplants are almost always grown in Production heated greenhouses where growing conditions are carefully managed. To grow quality transplants, it is important to optimize inputs like growing media, temperature, fertilization, water, and spacing needs. General Recommendation Table provides seed spacing and temperatures for seed germination and plant growing, and the time required to grow the plant to transplantable size. Quality plants are grown by using the appropriate trays and soil media, controlling germination, temperature and nutrients, and properly conditioning the plants for the field.

  Flats, Trays, and Pots

Use new flats and liners for transplant production to avoid pathogens that cause damping-off and other diseases. If old trays or liners are used, they should be thoroughly cleaned. Dip them in 10% chlorine bleach several times, then cover with plastic to keep them wet overnight. The bleach solution should remain below pH 6.8 to effectively kill disease pathogens (make a new bleach solution every 2 hours or whenever it becomes contaminated or diluted). Wash the trays with clean water to eliminate the chlorine, and let the flats dry prior to use. Wash exposed surfaces like benches, frames, and walls in the greenhouse to sterilize them as well. If plastic pots are reused, disinfest them as described above.

Seedling performance depends on cell size. Generally, transplants grown in larger cells (50’s, 72’s) produce earlier yields. Cell size does not affect total yield when growing seasons are long. If earliness is important, use larger cell sizes or bigger pots. While you may grow more plants per unit area of greenhouse in small cells (128’s, 256’s) and keep costs down, these trays may not be appropriate for some vegetables like melons. Transplant production cost depends on the number of plants grown per unit area and the length of time needed to grow the plant to plantable size.

Plant-Growing Mixes

There are many different pre-mixed growing media available and the best are lightweight, disease-free, and made from peat and vermiculite. Most commercial mixes produce quality transplants when used with good management practices. Commercial mixes can vary in composition, particle size, pH, aeration, nutrient content, and water-holding capacity. Most growers find a mix that works well for them and then continue to use it year after year. Avoid fine particle mixes which may hold excessive water and have poor aeration. If switching mixes, have them tested to determine the pH and nutrient levels in the media. Some growers blend their own media to reduce cost and to create a uniform, consistent composition. See Transplant mixes for pots, flats, or transplants trays table for some simple conventional and organic transplant growing mixes.

General recommendations for growing transplants from seed.

Crop Seeds / ft2 Seeding
Optimal Growth
 Asparagus 36 1/4 - 1/2  75  8-10  65-70  60 8-12 
Broccoli  48   1/4 85   65-70 60  5-7 
Cabbage  48  1/4  85   65-70 60  5-7 
Other Brassicas  48  1/4  80-85  4-6   65-70 60  6-8 
Cantaloupe  36   1/2 90  75-80  65  3-4 
Cucumber  36  1/2  90  70-75  65  3-4 
Eggplant  36  1/4  85  5-6  75-85  65  6-8 
Endive  60  1/4  70-75  65-70  60  4-6 
Lettuce 60-80 1/4 70-75 3 60-65 45 4-6
Onions 80-100 1/4 75 4-6 65-70 60 8-12
Other Leafy Greens 60-80 1/4 70-75 3-5 60-70 45-60 4-6
Peppers 36 1/4 85 8 75-80 65 7-9
Summer Squash 36 1/2 90 3 70-75 65 3-4
Sweet Potato --- 1/4 --- --- 75-85 65 5-6
Tomato 36 1/4 85 5-6 65-75 60 6-8
Watermelon 36 1/2 90 3 75-80 65 3-4

**Average number of weeks required to grow to transplantable size. Note: Temperature, light levels, nutrients, and other factors can influence grow times.

Transplant mixes for pots, flats, or transplants trays.

Tipi Potting Mix Recipe(Organic) Organic Potting Mix
  • 2 bales sphagnum peat moss (3.8 or 4.0 cubic foot bales)
  • 1 bag coarse vermiculite (4.0 cubic foot bags)
  • 1 bag coarse perlite (4.0 cubic foot bags)
  • 6 quarts of a fertilizing mix comprised of:
  • 15 parts steamed bone meal
  • 10 parts kelp meal
  • 10 parts blood meal
  • 5 to 10 parts dolomitic limestone (80 to 90 mesh)
  • 1 part sphagnum peat
  • 1 part peat humus (short fiber)
  • 1 part compost
  • 1 part sharp sand (builder’s)
  • To every 80 quarts of this add:
    • 1 cup greensand
    • 1 cup colloidal phosphate
    • 1½ to 2 cups crab meal or blood meal
    • ½ cup lime
Standard Vegetable Transplant Mix Organic Soil Blocking Mix
    Equal parts by volume of:
  • Vermiculite
  • Peat moss
  • Perlite
  • (use common liquid feeding program after seedlings emerge)
  • 3 buckets (10-quart bucket) brown peat
  • 1/2 cup lime (mix well)
  • 2 buckets coarse sand or perlite
  • 3 cups base fertilizer (mix equal parts blood meal, colloidal phosphate, and greensand together)
  • 1 bucket good garden soil
  • 2 buckets quality compost
Mix all components thoroughly and moisten to point where blocks hold together.