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Chapter 9: Transplant Production

9.1 Cultural Practices

Many crops are transplanted in New York because of the late spring, relatively short growing season, and desire to obtain maturity as early as possible. Transplants can be grown in greenhouses, plant beds, or field nurseries operated by vegetable growers or commercial plant growers. A good transplant is healthy, stocky, and relatively young with four to six true leaves. Such plants require uniformly fertile soil or mix, good light, even spacing, and proper temperature and water. Exposure to full sun outdoors or reduced temperature and watering near the end of the growing period toughen the plant and allow it to accumulate food reserves for starting the new root system after transplanting. Tender, very young, or weak plants often die. Overmature or hardened plants usually resume growth slowly and often have reduced yield and smaller fruit. Cabbage, broccoli, cauliflower, celery, and onion plants used for early spring planting may go to seed prematurely or "button" if subjected to cool temperatures during the growing period. Desirable daytime and minimum nighttime temperatures for growing plants and the approximate time required at these temperatures are listed in Table 9.1.1.

Table 9.1.1 Temperature requirements for plant production. (Temperature values are given in °F)

Crop Day Temperature Night Temperature Weeks from seed
Broccoli, Cabbage, Cauliflower 65 55-60 4-6
Celery 65 60 8-12
Eggplant 70-80 60 6-8
Lettuce 60-65 50 3-5
Melons 70-75 60 2-3
Onions 65-70 55-60 6-8
Pepper 70-75 60 6-8
Tomatoes 65-70 60 5-8

9.2 Growing Media

9.2.1 Soil

A good soil is characterized by at least four percent organic matter to give it good structure; medium texture (fine sandy loam or silt loam); medium to good fertility level; low soluble salts; pH of 6.0 to 6.8; and freedom from diseases and pests. Sufficient phosphorus (about two pounds of 0-20-0 per cubic yard) must be mixed thoroughly and uniformly with the soil. A soil test should be run well before use of any soil or compost, so necessary corrections in soluble salts, pH, and fertility levels can be made. Soluble salts should be kept below a K x 105 reading of 100 to 125, although muck soils can tolerate a somewhat higher amount without injury. Leaching and keeping the soil in the flat moist are partial solutions for high soluble salt problems. Refer to Section 9.6.1 for information on soil sterilization and control of diseases.

9.2.2 Artificial Mixtures

The artificial mix formula listed in Table 9.2.1 has proved practical for all vegetable plants. This mix is lightweight, does not crust, holds water well, and does not require sterilization. 

Table 9.2.1 Artificial mix

Material Amount for 1 cubic yard of mix
Shredded Sphagnum peat moss 11 bu
Horticultural vermiculite 11 bu
Ground limestone 10-12 lb
20% superphosphate (powdered) 2 lb
Calcium or potassium nitrate 1 lb
Fritted trace elements 3 oz
Iron (chelated such as 138, 330) 1 oz

Fertilizers should be spread evenly over the peat and vermiculite. Two ounces of nonionic water wetter, such as Aquagro, in ten to 20 gallons of water per cubic yard help to wet the mix. Mix the ingredients thoroughly on a clean floor or in a concrete mixer. Fill the flats, packs, or pots, and water thoroughly; wait approximately 15 to 30 minutes and water again. Transplant seedlings or sow seed in mixture. Do not plant too early because plants grow rapidly in the mix. For information on planting dates, see Section 9.5. In flats with transplants, apply a soluble fertilizer (one pound per 100 gallons of water) approximately three weeks after thinning or transplanting, and repeat once or twice a week. Calcium nitrate works well for this purpose.

9.3 Plant Containers

Old flats should be steamed before reuse because they may be contaminated with fungi capable of causing damping-off in seedlings. See Section 9.6 for details. Seeds are planted in wooden flats and plastic or Styrofoam® containers. The roots of vine crops (melons, cucumbers, and squash) need to be surrounded by a good mass of media, so seeds should be planted in plastic trays with individual cells filled with artificial mix or thin-walled peat pots filled with mix or soil. Peat pots must be soaked thoroughly before planting and set deep enough in the field for the soil to cover them completely. If few roots have penetrated the pots at time of setting, it may help to break out the bottoms. If conditions are dry after transplanting, extra water or irrigation may be needed to keep the soil moist inside the pot until the roots become established outside. In the trays, the mix will hold together well in pulling and setting if the root system is fairly well developed and the mix is moderately moist. These containers sometimes are used for early tomatoes, peppers, eggplant, and other transplanted vegetables.

9.4 Transplanting

Set plants in the field as soon as possible after pulling from field-seeded beds. Protect the roots from sun and wind between pulling and setting. Freshen roots of southern plants by running fresh water over them. To transplant, set plants one to two inches deeper than they were in the plant bed and firm the soil around the roots. Apply water using the transplanter or by irrigating immediately after transplanting, especially if the soil is somewhat dry. High temperatures or strong drying winds at the time of transplanting increase mortality and delay recovery. If possible, avoid planting under such conditions or be prepared to irrigate immediately.

9.5 Planting Dates

Table 9.5.1 includes approximate minimum and optimal temperatures for seed germination, the usual method of establishing the crop (use of transplants or crowns, root division, or direct seeding), and the range of dates on which each crop normally can be planted in New York State. See also Planting Method sections in individual crop chapters. Dates are given for planting commercial fields with either transplants or seeds as indicated. Plants to be grown in field nursery or plant beds should be started four to eight weeks earlier. Certain crops that are usually transplanted can also be seeded directly in the field under some conditions. Seeding should be done two to four weeks ahead of the usual transplanting date. Usual frost dates and other local weather or soil conditions must be considered in making final determinations of planting dates in each area. Most growers start planting when the first, favorable weather break occurs in or near the planting range indicated. Earlier plantings are possible with the use of row covers, hot caps, and other crop protection systems. See Chapter 7.

Table 9.5.1. Planting dates for commercial vegetable production in New York

Crop Germination (°F) Usual method of
establishing crop
Usual planting period
Minimum Optimal Plants Seed Fresh market Processing
Asparagus 50 75 crowns   April 15-May 15 April 15-May 15
Beans, dry 55 75   X   May 20-June 15
Beans, snap 55 75   X May 1-July 25 May 15-July 15
Beets 40 85   X April 1-July 31 May 1-June 30
Broccoli 40 85 X X April 1-July 31 July 1-July 20
Brussels sprouts 40 85 X   June 1-June 15 June 1-June 15
Cabbage 40 85 X   April 1-July 31 May 1-July 10
Cabbage 40 85   X April 15-July 10 April 25-June 25
Carrots 40 85   X March 25-June 30 May 1-June 15
Cauliflower 40 80 X X April 1-July 31 July 10-July 31
Celery 40 70 X   May 15-June 30  
Chinese cabbage 40 75   X May 15-July 15  
Cucumbers 60 75 X X May 15-June 30 May 25-June 15
Eggplant 60 85   X May 20-June 10  
Endive 35 75   X June 15-July 15  
Lettuce 35 75 X X March 25-July 15  
Muskmelons 60 95   X May 20-June 10  
Onions 35 80 X X March 25-April 30  
Peas 40 75   X April 1-May 15 April 10-May 15
Peppers 60 85 X   May 15-June 15  
Potatoes, muck - - tubers   April 25-May 15 April 25-May 15
Potatoes, upland - - tubers   April 1-May 31 April 1-May 31
Pumpkins 60 95 - X May 15-June 10 May 25-June 15
Radishes 40 85   X April 1-August 31  
Spinach, spring 35 70   X March 15-April 30 March 25-April 30
Spinach, fall 35 70   X July 15-August 31 July 25-August 10
Squash, summer 60   95 X May 15-June 30  
Squash, winter 60 95   X May 15-June 15 May 15-June 15
Sweet corn 50 85   X April 15-July 10 May 15-June 20
Tomatoes 50 75 X X May 1-June 15 May 20-June 10
Turnips 40 85   X July 1-August 10  
Watermelons 60 95   X May 25-June 5  

9.6 Disease Management

Minimizing disease problems in the greenhouse starts long before planting. Maintain a one-month crop-free, weed-free period to break pest cycles. Disinfect walls, walkways, benches, and pipes in production houses, and seal for three to four days prior to planting. Routinely disinfect walkways and tools. Continuously remove and destroy any old or diseased crops and all weeds, from inside and bordering outside of greenhouse, as these may harbor insects and diseases. Avoid piling plant residues near the greenhouse to minimize potential disease reintroduction. Finally, clean hands, tools, and boots or shoes prior to entering a clean greenhouse to minimize disease spread.

Growing transplants successfully involves control of damping-off fungi often present in the soil. Seed treatments alone are not enough. Unfortunately, few chemicals are registered for vegetable bedding plants; any chemical usage must go hand in hand with good cultural practices. Ridomil Gold EC may be used on broccoli, cabbage, Chinese cabbage, cauliflower, cucurbit vegetables, head lettuce, spinach, legume vegetables, onions, and tomatoes for the control of Pythium damping-off. Consult the label for the appropriate rates and method of application. Note that this is for seedlings planted in beds and not transplants grown in flats in an enclosed environment, such as greenhouses or glasshouses.

Rely on the use of light, well-drained soils or soilless mixtures free of pathogens; careful control of moisture, light, and relative humidity; and soil drenches (on certain crops) to reduce disease.

Damping-off becomes more troublesome when plants and soils are overwatered, excessively shaded, and permitted to remain wet for long periods. Water only in the bed or flat. Keep humidity as low as possible by ventilating properly. Automatic fan ventilation is ideal for plant-growing houses.

9.6.1 Soil Sterilization

Soil to be used for growing transplants in flats can be sterilized by steam or chemicals. With steam, the entire soil mass should be brought to a temperature of 180°F for 30 minutes. Add organic matter, superphosphate, and other fertilizers before sterilization. Leach the soil after sterilization to reduce soluble salt accumulation. Store the soil for two weeks before use to avoid plant damage from toxic materials released during steaming. Use a plastic seal with chemicals; be sure the soil temperature is 55°F or above, and provide waiting periods of four to 14 days. With adequate ventilation, the following chemical is suitable for this purpose: one quart of *Vapam HL in five gallons of water over 1/2 cubic yard. For outdoor plant beds or seedbeds in fields, the following chemical can be used after preparing the soil as for seeding: one pint of *Vapam HL per 50 square feet, applied as a drench and sealed with water. Follow label directions for timing, crop safety, and method of application. In general, soils must be at least 55°F at the six inch depth, and a lapse of 14 days between treatment and seeding must be allowed; 21 days is better.

*Methyl bromide requires only two to three days after uncovering. Do not use *Methyl bromide for soils in which onions will be grown. Artificial soils do not require sterilization.

9.6.2 Flat Sanitation

All flats should be steamed before reuse. They can be stacked on a bench or the floor and covered with a tarpaulin beneath which steam is released. Minimum treatment should be 180°F for 30 minutes. Flats should be separated horizontally by 3/4 inch strips or stacked in a staggered manner with vertical spaces of about one inch. Flats can be used immediately.

If steam is not available and chemicals must be used, chlorine solutions (one part laundry bleach to nine parts water) are probably the most effective sanitizers. Apply by dipping the flats and draining the solution back into the tank. Stack the flats under a tarpaulin for 24 hours; then uncover, but keep them wet by spraying with water until the odor is gone. This usually takes four to six days. To be sure flats are safe for use, put a wet one in a plastic bag for 24 hours, and check the closed bag for odor.

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Maintained by Abby Seaman, New York State IPM Program. Last modified 2020.