Starting and growing
transplants under lights
Curtis Swift, Swift Horticultural Enterprises, LLC
Introduction:
Transplanting is the process of shifting of plants from
one place or growing medium to another. If done properly plant stress will be
minimized and the production of flowers, fruits, and foliage can be enhanced.
Starting your own transplants (seedlings) indoors under
lights or in a greenhouse where adequate light is available avoids problems with
direct seeding into garden soil where seedlings often have to battle their way through
soil crusts. Starting your own transplants can result in higher quality plants
and cultivars that are not available at local greenhouses or garden centers
Starting plants indoors under lights the seeds germinate
under ideal conditions. Starting them at the proper time can extend the growing
season and create earlier harvest when compared with direct seeding in the
field. Transplants you grow are typically not exposed to the myriad of virus,
fungal or insect problems commercially-grown transplants may be exposed
to. While it is often difficult to
pinpoint when a transplant was exposed to a problem, the timing of symptom
development often leads one to suspect the origin of the infection was the
commercial greenhouse. Your goal is to produce vigorous and healthy plants
ready to be planted in the garden when conditions are appropriate.
Not all vegetables are worth the effort to start as
transplants. Even though you can grow them from seed in the home or greenhouse,
it is difficult to successfully transplant these to the garden. These include carrots
and beets, leafy biennial herbs (dill), heading types of Chinese cabbage, and cucurbits
(cucumbers, pumpkins, squash); they don’t like their root systems disturbed.
Radish, leaf lettuce, and spinach develop so quickly when
seeded in the garden starting them as transplants is not worth the effort. Radishes
are often ready to eat in fourteen days from the time of seeding.
Vegetables such as tomatoes, peppers, eggplant, okra, head
lettuce, and broccoli are typically started as transplants and that is where I
would suggest you focus your efforts. Sweet potato grown from rooted cuttings
is another vegetable that would benefit from being started in the home.
Age affects transplant quality:
Smaller,
stocky plants that have not started to bloom and/or set fruit adapt to the
garden more easily than leggy transplants or plants with small fruits. Tomato
plants four to five weeks old grow and produce a higher yield than older
transplants. The younger transplants often develop healthy root systems which
helps avoid problems with the splitting of the fruit and blossom-end rot common
when older transplants are used. Using
younger plants does not guarantee these problems will be eliminated but helps control
these problems. The ideal plant is short and stocky, which for many transplants
will be about six inches tall and six inches wide. The table at the end of this
article provides the recommended age for vegetable transplants when planted
into your garden. Since transplants are more susceptible to cold than plants
direct-seeded to the garden, transplants are usually planted after the average
last spring freeze unless some form of frost protection is provided. If you know
that date, count back the number of weeks indicated on the table, add the
number of days needed for germination, and plant the seed accordingly.
Problems you need to
avoid:
Low
light, excessive levels of nitrogen, and high temperatures during transplant
development causes excessive stem elongated.
Such stems are more susceptible to diseases and breakage. In most cases
the diseases that attach young seedlings are the result of using soils
(planting media) that have not been properly pasteurized. If you insist on mixing your own planting
media for seedlings, it should be placed in the oven and cooked to eliminate
all the water-molds and other plant pathogenic organisms that live in that
soil. Pasteurization occurs when the soil is moist allowing heat to reach every
bit of soil. Forty-five minutes in a two-hundred degree oven usually does the
trick. If you have a temperature probe insert that into the center of the soil
mass and when the temperature reads one-hundred and eighty degrees for thirty
minutes the soil has been properly pasteurized.
Exceeding that temperature for longer than thirty minutes is not
recommended.
Damping-off is caused by fungi or fungal-like organisms
which attack the base of the stem next to the planting medium. Non-pasteurized
planting medium, the use of dirty flats, trays, or pots, and dirty tools are
often the cause. Fungus gnats can also carry some of these plant pathogens from
contaminated house plants to your seedlings.
The
best planting medium for starting seedlings are the soil-less mixes. They are usually free of pests, have good
water-holding capacity, are well aerated and drain properly, and are low in
salts. Some even have fertilizers added
to help keep your young seedlings perking along in a healthy condition. This doesn’t mean however, you don’t have to
fertilize.
Transplants
can be started in individual pots, cubes or open flats. When started in open
flats, the young seedlings will need to be pricked out (transplanted) and
repotted in individual pots when the seedlings have their first true leaves. Some
gardeners will do this by pulling the tiny plant out of the flat of planting
media by their seed leaves. This is a fast and easy way to do transplant a
large number of seedlings but can be damaging to the plant. Some gardeners remove
the tiny seedlings with sharpened Popsicle stick.
Lights:
Plants grown without sufficient light are yellow or
lighter green than they should be. These
plants are said to be chlorotic. They stretch for the light, have thin stems,
and in general are not as healthy as plants grown with adequate light. Gardeners
who depend on natural light for the proper development of their seedlings cannot
produce quality transplants.
The light used by plants comes in different frequencies
and the packets of energy carried by the different frequencies energize
different responses in the plant. Exposure to red light increases seed germination
while far-red light increases legginess. Since regular incandescent bulbs
produce more far-red light than fluorescent lights, the latter are preferred
for seedlings. To ensure adequate light
reaches all parts of the seedling, fluorescent lights should be placed no more
than four inches above the top of the plant. The plants need to be spaced far
enough apart so shade is not a problem. Full spectrum grow lights are recommended
if you have fixtures with only one tube but if you have a two-tube fixture one
cool-white and one warm-white tube provides the same spectrum of light.
If you decide to use incandescent lights for your seedlings,
they need to be placed between one foot and three feet from the top of the
plants even then you might burn your seedlings unless you use bulbs
specifically designed for plants. The Spot Grow type incandescent bulbs are
said to provide the proper plant growth enhancing light characteristics. Plastic
sheeting is available designed to reduce the amount of far-red light and is an
option for those growing transplants with incandescent bulbs.
Temperature:
Plants placed on the window sill, while not providing adequate
light, also are subjected to large temperature fluctuations between day and
night and sunny and cloudy days. Temperatures cooler than optimum often increase
disease problems and can cause the development of rough fruit in tomatoes and
bolting (i.e. development of a seed stalk) in onions and other biennial
vegetables. Warmer than optimum temperatures can cause weak and spindly
seedlings.
Fertilizing
your transplants:
Nitrogen (N) is what your seedlings require to develop into
healthy transplants and different types of vegetable seedlings require
different rates and frequencies of applying nitrogen. Tomato seedlings need to
watered with fifty to one-hundred parts per million (ppm) of N or once a week
with water supplemented with two hundred and fifty to three hundred ppm of N. Peppers
prefer a daily watering containing one-hundred ppm of N, while cole crops
(cabbage, broccoli, cauliflower, etc.) prefer one-hundred to one-hundred and
fifty ppm of N per week. The vine crops (squash, pumpkin, etc.) need two to
four applications of one-hundred to one-hundred and fifty ppm of N per week.
Ok, now that the amount of N these transplants require has
been provided, how do you mix up a solution containing one-hundred ppm of N?
When you purchase a granular or liquid fertilizer at a garden
center it will most like give the percentage of N along with the percentage of
phosphorus (P), potassium (K) and other nutrients. The container may also give the parts per
million but this is seldom the case. The percentage of N in the product is easy
to convert to ppm as follows:
10% = 100,000 ppm
12% = 120,000 ppm
15% = 150,000 ppm
20% = 200,000 ppm
and so forth.
Now that you know the ppm of N in the product you purchased,
you need to dilute with water to obtain the ppm of N needed by your seedlings. This
is quite easy to do with a liquid fertilizer as you are adding a liquid (the
fertilizer) to a liquid (the water). With a granular product you have to turn
the fertilizer into a liquid. This is
done by adding it to water. Measure out a measured amount of water and add sufficient
dry fertilizer to double the level of the water in the container. This will reduce the percentage of the
fertilizer by half; a 20% N dry fertilizer will then contain 10% N.
You will need a pipette, eye dropper, or small measuring cup
like those that come with cough syrup to dilute the fertilizer product to what
is needed by your seedlings. These are usually marked in milliliters and that
is what you need.
The formula you need to use is Ci x Vi =
Cf x Vf where
C = ppm
V = volume in milliliters
i = initial
f = final
If you have a product that contains 12% N (120,000 ppm) and
need a final solution of 100 ppm of N, plug 120,000 into the formula at Ci.
Let’s make one gallon of this mix. One gallon is 3,800 ml so the formula Ci
x Vi = Cf x Vf will look like this:
120,000 ppm x Vi = 100 ppm x 3,800 ml. When you do the
computations you receive the number of milliliters (3.2) that need to be added
to one gallon of water to create a N solution of 100 ppm.
If you want to make less than a gallon, plug the following
into Vf:
1 quart = 950 ml
1 pint = 475 ml
1 cup = 240 ml
To make one gallon of a 100 ppm N fertilizer solution it
will take:
3.8 ml of a 10% N fertilizer product
3.2 ml of a 12% N fertilizer product
2.5 ml of a 15% N fertilizer product
1.9 ml of a 20% N fertilizer product
Hopefully this article helps you grow healthy vegetable
transplants.
Table 1
Vegetable
|
Soil
Temperature for seed Germination 1
|
Time
Required
for growing Plants
for Field Transplanting 4
|
|
Optimum
Range
(oF)
|
Day
2
(oF)
|
Night
(oF)
|
Time
(weeks)
|
Asparagus
|
60
- 85
|
70
- 80
|
65
- 70
|
8
- 10
|
Broccoli
|
68
- 86
|
60
- 70
|
50
- 60
|
5
- 7
|
Brussel
Sprouts
|
75
|
60
- 70
|
50
- 60
|
5
- 7
|
Cabbage
|
45
- 95
|
60
- 70
|
50
- 60
|
5
- 7
|
Cauliflower
|
45
- 85
|
60
- 70
|
50
- 60
|
5
- 7
|
Celery
|
60
- 70
|
65
- 75
|
60
- 65
|
10
- 12
|
Corn,
Sweet
|
60
- 95
|
70
- 75
|
60
- 65
|
3
- 4
|
Cucumber
|
60
- 95
|
70
- 75
|
60
- 65
|
3
- 4
|
Eggplant
|
75
- 90
|
70
- 80
|
65
- 70
|
6
- 8
|
Lettuce
|
40
- 80
|
55
- 65
|
50
- 55
|
5
- 7
|
Muskmelon
|
75
- 95
|
70
- 75
|
60
- 65
|
3
- 4
|
Okra
|
85
- 95 3
|
70
- 75
|
65
- 70
|
4
- 6
|
Onion
|
50
- 95
|
60
- 65
|
55
- 60
|
10
- 12
|
Pepper
|
65
- 95
|
65
- 75
|
60
- 65
|
6
- 8
|
Squash
/ Pumpkin
|
70
- 95
|
70
- 75
|
60
- 65
|
3
- 4
|
Tomato
|
60
- 85
|
65
- 75
|
60
- 65
|
5
- 7
|
Watermelon
|
70
- 95
|
70
- 80
|
65
- 70
|
3
- 4
|
1. Adjust temperatures slightly to
alter growth rates.
2. Select the lower temperature on cloudy days. Daily fluctuations to 60o
F. or lower at night is essential for some vegetables.
3. A hard seed coat prevents good germination. Treatment of seeds with
concentrated sulfuric acid for 2-3 hours or soaking seeds in hot water (113 o
F) for 1 1/2 hours improves germination.
4. Transplants older than recommended suffer more shock when transplanted to
the garden and often produce less of a crop over the course of the growing
season than transplants of the proper size and age.
References used:
Lorenz, O.A., and D.N. Maynard. 1988. Knott's Handbook for Vegetable Growers,
Third Edition. Wiley-Interscience Publications
Splittstoesser, W.E. 1984. Vegetable Growing Handbook, Second Edition. AVI Publishing
Company, Inc.
Yamaguchi, M. 1983. World Vegetables; Principles, Production and Nutritive
Values. Van Nostrand Reinhold Company.
