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Leggy Lettuce Seedling Problem

Posted by mrmossy 9 (My Page) on
Tue, Aug 14, 07 at 11:15

I just started some lettuce seedlings for the fall and am having a real problem producing strong stems on the plants. See the photo, these plants are two weeks old and the stems are so thin that they can not stand up on their own.

The seeds were started in peat pellets with 3 seeds in each pellet. They are in my garage under growing lights and I have been keeping the lights no further then 2" away from the top of the plants for 16 hours each day. I had a fan on them for a few minutes each day for the first week to increase air circulation and promote strong stems. Once the plants were around 1" tall they were thinned to one plant per pellet.

I had the same problem last Spring with my lettuce started in the trays. However in the Spring I had the trays in a sunny southern facing window. After the plants were a couple of weeks old none of them could stand on their own due to the thin stems. So, for the fall I decided to try the growing lights but ended up with the same result.

Am I doing something wrong? How do I get strong stems on these lettuce plants?

Follow-Up Postings:

RE: Leggy Lettuce Seedling Problem

Some varieties don't do well in grow cups. I had a greenhouse grower start some collard seeds for me and she had the same problem. The ones' that I had in the ground were not leggy at all had strong stems. These were volunteers. Wish you luck. Dale

RE: Leggy Lettuce Seedling Problem

There are actually 4 different varieties that are all having the same problem - Parris Island Cos, Green Ice leaf, Black Seeded Simpson leaf, and New Red Fire leaf. Does leaf lettuce in general not do well started indoors? Thanks.

RE: Leggy Lettuce Seedling Problem

If you are using a cheap shop light from Wal-Mart, it may be using T12 fluorescent bulbs at 20 Watts per bulb (most T12 fixtures are 40 Watts per tube). I am assuming bulbs of 48 inches. So 2 inches from the growing surface may still not be enough.

I got a light meter for $30 at a hydroponics store. It was well worth the investment; my only complaint is that its max reading is 1/2 solar (5000 foot candles). I have my indoor grow lights set to 1250 to 2500 foot candles at the growing surface, which is about 1/8 to 1/4 solar. I'm mostly using T8 fluorescent bulbs, with the electronic ballast in the fixture replaced and rewired in order to "overdrive" the bulbs with twice the normal amount of "juice" (from 30 watts to 60 watts per bulb). Gardenweb has a forum on indoor plant lighting, which has had threads about overdriving. Otherwise, aquarium forums also discuss this.

Even at 1/8 to 1/4 solar, red lettuce cultivars require full solar to get full color. And loose leaf cultivars are taller than outdoor seedlings. By the way, a brightly lit indoor room is usually 1/100 solar at best.

RE: Leggy Lettuce Seedling Problem

Were the seeds burried in the soil? If not is it possible that fan blew some soil over the seeds? Or did the peat pallets cast some shadow blocking the light?
npthaskell has explained nicely the light necessary for germinating Lettuce seeds.
I believe the Lettuce seeds need direct exposure of sun light (or right kind grow lights as npthaskell has explained) in particular the R and Rfr components to signal healthy germination of Lettuce seeds.

RE: Leggy Lettuce Seedling Problem

Thanks for the information. I am using T12 tubes rated at 40 Watts each. They are from Ott-lite and were labeled as plant growing bulbs. I will have to invest in a light meter to figure out what the foot candle reading was. You said that your light reading was 1250 to 2500 - is that sufficient for growing lettuce?

The seeds were about 1/8" below the soil surface when I planted them. Would I get better results if I put them on the soil surface instead so they could get direct light when germinating?


RE: Leggy Lettuce Seedling Problem

1250-2500 foot candles is OK for growing lettuce indoors; that is what I do during winter time. Actually, I tend to move them in and out depending on winter weather.

The Ott-lites should be OK at 2 inches from the plants unless your fixture only runs them at 20 watts instead of 40 (these are nominal, by the way). How many bulbs are you using?

I think that 1/8 inch below the surface is OK.

Last resort...maybe you should move your peat pellets outdoors 4 days after germination instead of 2 weeks?

RE: Leggy Lettuce Seedling Problem

Mr. Mossy,
Do not plant your lettuce on the surface. I germinated some last month on a wet paper towel and then scattered them on the surface and sprinkled sand on them. They were also leggy. I will go back to 1/8 or a little deeper next time.
1eyedJack and the Dawg

RE: Leggy Lettuce Seedling Problem

in the summer I grow buttercrunches and in the early spring and fall I grow romaines, all started under lights in my basement. Every year the buttercrunches are leggy and the romaines are strong. I've always thought it was the buttercrunch variety. But onces they are planted in the garden (a little deeper so they stand up) they are fine. Seeds sown directly in the garden are no different.

just my two cents

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