I'm curious if I'm doing my lighting right for my seedlings. I have
one of the Professional Jiffy Greenhouse 72 peat pellet seed starting
kits, and I'm starting my seeds for my garden.
Anyway, I have two 18" flourescent fixtures- one with a GE Plant &
Aquarium tube, and one with a GE Chroma 50 tube. I set the
fixtures/tubes directly on the plastic greenhouse top, and rotate them
each day, so that the plants get an even mix of Chroma 50 and Plant &
The vast majority of the seeds sprouted quick, and are growing madly-
most of them have their cotyledon leaves & stems almost to the top of
the plastic greenhouse top- they look kind of spindly right now. No
true leaves have shown up yet.
Is this a problem, or is it common for the cotyledon leaves to shoot up
really high and quick? I read that lack of light will cause leggy
plants, but I'm not short of light with my setup, am I?
You are a bit ahead of schedule, aren't you? Its only February and in most
places, you are long way off before it is safe to put plants outdoors.
What plants are you growing from seeds anyway?
You should try to have your plants as close to the lights as possible
without burning them.
What length day are the lights set for?
If you use a light meter, you will see that the light intensity emanating
from plant lights is far less than what you would get outdoors or in a
greenhouse. Its even less than you would get in a shaded locality outdoors.
Another problem with growing under artificial lights is poor air circulation
and too high humidity. That can cause the seedlings to come up spindly and
too weak to survive for long. You need to get a small fan and set it on a
low setting just to move the air around.
Totally depends on where he lives. He's not ahead of schedule here in
Zone 9. I already have six flats of seedings well under way.
the plastic greenhouse top<
I'm not familiar with the Jiffy Greenhouse, but if it has a removable
greenhouse top, it should be removed when the first seedlings sprout.
How long are you leaving the lights on? The plants need around 16 hours
of light from fluorescent fixtures. Make sure you keep the tubes as
close as you can to the seedlings without them touching.
Cereus' suggestion for a fan is a good one. Also, to strenghthen the
seedlings' stems, gently run your hands over the tops of them every
day, lightly brushing them a bit.
You're right on target then. Most seeds should be planted 6 to 8 weeks
before the last frost.
Definitely take off the lid. It'll help with air flow, and if there's a
lot of condensation on the lid, it may be cutting down some of your
I'd try a small oscillating fan closer to the seedlings. I have mine
set up in a closet, so a small fan is sufficient to keep air
circulating around the plants. If it doesn't oscillate, I wouldn't
point the fan directly at the seedlings as it might dry out the potting
Another thing I do is to surround the planting trays with a small
"wall" of aluminum foil, which bounces more light back on to the
seedlings. This definitely helps with the seedlings I place on a sunny
window ledge, as I don't even have to turn the trays around -- the
seedlings no longer lean toward the sun when the light is reflected on
|> |> Is this a problem, or is it common for the cotyledon leaves to shoot up|> really high and quick? I read that lack of light will cause leggy|> plants, but I'm not short of light with my setup, am I?
The usual cause is too much heat relative to the light, which is
a nightmare in the UK - we can get leggy seedlings OUTSIDE in
Try keeping them cooler, at least from when they start to emerge
from the compost.
you are definitely short of light. the other pieces of advice are
pretty good, and they will improve your light efficiency and prevent
damping off, but they won't solve your main problem, which is too
little light. You can evaluate things yourself. In full sun, with the
sun overhead you get about 600W/m2 of light. With the sun at 45
degrees, you get 420W/m2. Each 72-cell tray is about 0.18m2, so you
should be coming in with close to 80W/tray. Those fluorescents are
fairly efficient, but they are not 100% efficient, so make that
100W/tray. I found that the only thing that helps is a sunny window,
and taking them out to full sun as soon as feasible.
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