Southeastern U.S. Vegetable Crop Handbook - 2022 - 34

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 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 recommended
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.
Transplant Height Control. The goal of a transplant producer
should be to produce a strong transplant with sturdy growth that
can withstand transplanting into the field. Tall, spindly, or overgrown
transplants can be difficult to remove from the transplant
tray and might become entangled in the transplanting equipment.
There are a few methods available that can aid the producer to
control the top growth of developing transplants. One method is
to use cold water for irrigation, 33-34°F, which has been shown
in some species to control top growth.
Brushing the plants, or setting up fans so that the plants
are moved (brushed by air) is another method. This results in
a mechanical stress of the plant stem and can result in shorter
plants overall. The intensity and frequency of brushing will
have to be adjusted to avoid damage to developing foliage
while still achieving height control.
Chemical Hardening. Recently, a label for Sumagic™
(uniconazole) has been released allowing foliar sprays on the
following vegetable transplants: tomato, pepper, ornamental pepper,
eggplant, tomatillo, ground cherry, and pepino. But the new
label is rather restrictive; the maximum total allowed application
is 10 ppm at 2 quarts per 1,000 square feet. This means only one
10-ppm spray, two 5-ppm, or four 2.5-ppm sprays are allowed,
and so on. The final spray must be made no later than two weeks
after the two- to four-leaf stage, about four to six weeks after
sowing.
For production of retail tomato transplants in six-packs to
4-inch pots, we recommend an initial uniconazole spray at 1 to
2.5 ppm two weeks after sowing. If additional height control is
needed, up to three additional applications of 1 to 2.5 ppm can
be made at seven-day intervals. Until we know more about the
post-harvest effects and the range of sensitivity each cultivar
demonstrates, we recommend growers avoid the use of higher
rates in excess of 5 ppm. Uniconazole is a highly active PGR
(plant growth regulator), it is critical to emphasize that caution is
paramount while implementing uniconazole for vegetable transplant
height control.
Cultural Methods for Hardening. Cultural methods used to
harden transplants employ reducing water and altering the ambient
temperatures. Combinations of these two methods are
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2022 Vegetable Crop Handbook for Southeastern United States
Southeastern U.S. Vegetable Crop Handbook - 2022

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