Southeastern U.S. Vegetable Crop Handbook - 2021 - 28

Commercial Plant-growing Mixes. A number of commercial media
formulations are available for growing transplants. Most of
these mixes will produce high-quality transplants when used with
good management practices. However, these mixes can vary greatly
in composition, particle size, pH, aeration, nutrient content, and
water-holding capacity. Avoid formulations having fine particles,
as these may hold excessive water and have poor aeration. Have
mix formulations tested by your state's soil test laboratory to determine
the pH and the level of nutrients the mix contains.
Treatment of Flats. Flats used in the production of trans plants
should be new or as clean as new to avoid damping-off and other
disease problems. If flats are to be reused, they should be thoroughly
cleaned after use and completely submerged in a household
bleach solution for at least 5 minutes. Use 5 gallons of 5.25% sodium
hypochlorite (such as Clorox) for each 100 gallons of solution
required. Permit flats to dry completely prior to use. Never treat
flats with creosote or pentachloro phenol.
Plant Containers: There are a wide variety of containers available
for starting seeds for transplants. Most growers start seeds either in
flats or in cell packs.
The main advantage of using flats is that more plants can fit
into the same space compared to cell packs. However, if you start
seeds in flats, you will need to transplant to larger cell packs or to
individual pots as the seedlings get bigger.
Seeding directly into cell packs saves time, because transplanting
into a larger container later is not necessary. Cell packs
come in many different cell sizes; the overall tray size is standardized.
For tomatoes and peppers, 72-cell packs work well. For larger-seeded
vegetables; such as cucumbers, squash, and watermelons,
48-cell packs work better.
Each vegetable crop has specific cell sizes for containerized
transplant production and requires a certain number of weeks before
they are ready for transplanting (Table 5). For example: broccoli,
Brussels sprouts, cabbage, cauliflower, and collards require a
0.8 to 1.0 inch cell and 5 to 7 weeks to reach an adequate size for
transplanting; cantaloupe and watermelons require a 1.0 inch cell
TABLE 5. OPTIMUM AND MINIMUM TEMPERATURES FOR
TRANSPLANT PRODUCTION
°F
°F
Broccoli
Cabbage
Cantaloupe1
Cauliflower
Cucumber
Eggplants
Endive & Escarole
Lettuce
Onions
Peppers
Summer squash
Sweetpotato
Tomatoes
Watermelon, seeded
Watermelon, seedless
1
Cantaloupe and other melons
28
Opt. Day
65-70
65
70-75
65-70
70-75
70-85
70-75
60-65
65-70
70-75
70-75
75-85
65-75
85-90
85-90
Min. Night
60
60
65
60
65
65
70
40
60
60
65
ambient
60
80
85
Weeks
to Grow
5-7
5-7
3-5
5-8
2-3
5-8
5-7
5-6
8-12
5-8
2-3
4-5
5-6
3-5
3-6
and 3 to 4 weeks; eggplant and tomato require a 1.0 inch cell and
5 to 7 weeks; and pepper requires a 0.5 to 0.8 inch cell and 5 to 7
weeks. Other options are available depending on the crop and your
situation.
Seed Germination. Seed that is sown in flats to be " pricked out "
at a later date should be germinated in ver miculite (horticultural
grade, coarse sand size) or a plug growing mix. However, it
is recommended that no fertilizer be included in the mix or the
vermicu lite and avoid fertilizing the seedlings until the seed leaves
(cotyledons) are fully expanded and the true leaves are begin ning
to unfold. Fertilization should be in the liquid form and at one-half
the rate for any of the ratios listed in the following section on " Liquid
Feeding. " Seedlings can be held for a limited time if fertilization
is withheld until 3 to 4 days before " pricking out. " Seed that is
sown in pots or other containers and that will not be " pricked out "
later can be germinated in a mix that contains fertilizer.
To get earlier, more uniform emergence, germinate and grow
seedlings on benches or in a floor-heated greenhouse. Germination
can be aided by using germination mats which provide heat
directly to the trays. With supplemental heating such as this,
seedling emergence and uniformity can be enhanced decreasing
the amount of time required to produce a transplant. If floor heating
or benches is not available, seed the trays, water, and stack
them off the floor during germination. Be sure to unstack trays before
seedlings emerge.
Heating and Venting. Exhaust from heaters must be vented to the
outside. It is also recommended to have an outside fresh air intake
for the heaters. Be sure vents and fans are properly designed and
positioned to avoid drawing exhaust gases into the greenhouse. Exhaust
gases from oil and improperly adjusted gas heating systems
can cause yellowing, stunting, and death of seedlings. Do not grow
or hold seedlings in an area where pesticides are stored.
Liquid Feeding. The following materials dissolved in 5 gallons of
water and used over an area of 20 square feet are recom mended for
use on the transplants if needed:
20-20-20 1.2-1.6 oz/5 gal water
15-15-15 2 oz/5 gal water
15-30-15 2 oz/5 gal water
Rinse leaves after liquid feeding. Fertilizers used for liquid feeding
must be 100% water soluble.
When transplanting to the field, use a " starter fertilizer " being
sure to follow the manufacture's recommendations.
Watering. Keep these mixes moist but not continu al ly wet. Water
less in cloudy weather. Watering in the morning allows plant
surfaces to dry before night and reduces the possibility of disease
development.
Hardening and Transplant Height Control. Proper hardening of
transplants, stiffens stems, and hardens the transplants increasing
their survival.
There are several methods - chemical and cultural - used to
harden transplants and the choice of which to use is often crop-dependent.
At this time there is one chemical plant growth regulator
available for use in producing vegetable transplants but its use is
limited to several solanaceous crops.
2021 Vegetable Crop Handbook for Southeastern United States
Southeastern U.S. Vegetable Crop Handbook - 2021

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