'fixing' bending stems on lettuce

skubes50May 4, 2009

First off, thanks everyone for contributing - it has helped a newbie like me tons. Here is my deal: have (2) small 3 gal. bubbler systems going, on about week 3 from start of germination. I have 4 lettuce seedlings that I am concerned about because the stems of all of them are bending over. I currently have them propped up with cocktail toothpicks, but need to have a more permanent solution.

So, first need to know why this happened....

I have a 175 watt MH above at about 18", air temp is 70F, humidity at 50%, pH at 5.8-6, and TDS at 380.

I know lettuce sometimes bolts, but I germinated under cooler temps to help prevent this. What do you think?

Next, I think to 'fix' these stems I will try to put about 3/4" of additional rockwool around exposed stem (spliced down the middle) and kept together with a rubberband aroud it , basically to help support. Have I confused you all enough? Thanks in advance for all of your help!

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Karen Pease

I have 4 lettuce seedlings that I am concerned about because the stems of all of them are bending over.

Sounds like they're leggy from insufficient light. Try lowering your lamp.

    Bookmark   May 4, 2009 at 5:18PM
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I currently have a 175 watt MH light about 14 inches above the plants. Right after they sprouted, I moved them from the germination tent to under the MH , which was about 24" above. I think they are now receiving sufficient light, but maybe because of the original gap between they are now not strong enough. Do you think the built up rockwool will help? Thanks

    Bookmark   May 4, 2009 at 6:14PM
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Karen Pease

Well, try the standard test for fluorescents and HID -- put your hand under the bulb where you want your plants to be. It should feel nice and cozy-warm, but not hot. If it doesn't, adjust. Get the plants as close as you can to the bulb without entering the "hot" zone. You'll be able to get them a little bit closer if you have good air circulation than you would if you don't.

175W isn't much for MH unless you're only covering a small area.

    Bookmark   May 4, 2009 at 6:41PM
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Over the past 18 months I have started about 8 batches of lettuce seedlings in 1" rockwool cubes, 2 seeds per cube, and the majority were leggy. I propped them up with cocktail toothpicks. Then I heard about the more light solution, so I exposed them to light. It didn't work, so I decreased the distance between the light source and seedlings. It didn't make a noticeable difference. So folks have suggest exposing them to a light breeze, I haven't tried that.

Bottomline: I have found that seedlings being leggy doesn't make any difference to lettuce production. Almost immediately after transplanting to my raft system, the seedlings' stems beef up and the plant grows upward.

    Bookmark   May 6, 2009 at 12:37PM
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Karen Pease

It is a light issue, but the problem is that lettuce is one of the easiest plants to go leggy. It needs a ton of direct light to hold itself up vertically. Wind doesn't hurt, either.

    Bookmark   May 6, 2009 at 1:48PM
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I know exactly what you're talking about - you get a length of stem above the medium below the first leaves and it falls over.

What I do is just bury it deeper when I put it in the garden, or when it goes into the net pot, so that the new surface is even with the crown of the plant.

Whatever the case, if you put a fan on them and let them grow they'll strengthen up and be fine. Even if the stem goes sideways for a bit it'll bulk up and anchor the plant well enough.

    Bookmark   May 7, 2009 at 6:53PM
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May I ask what lettuce variety you are using? The folks here are correct saying it is a light problem. Lettuce is a sun loving crop. It requires the full spectrum of light to grow well.

However, there are lettuce varieties that are more what we call 'bolt tolerant' Bolting is the tendency of the crop to be leggy due to low light or extreme hot weather. Now when you buy your lettuce seeds, ask of they are bolt tolerant. TO give you an idea, most of the red lettuce like Lollo Rossa and red batavia does are not as leggy as the green ones like the romaine, lollo bionda or even iceberg lettuce.

If you cannot find these varieties, then you need to solve your light issue. There are two grades of MH or sodium vapor lamp. There are the industrial grade and the horticultural grade. You can ask about this from the manufacturer. Horticultural grade ones provide more or less the same visible light spectrum similar to the sun.

Good luck

Here is a link that might be useful: plants and more

    Bookmark   May 12, 2009 at 4:08AM
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Thanks everyone for the helpful suggestions. It indeed was a light problem. When I lowered it to about 10" from the top of the plants they instantly perked up and are still thriving. The variety I am growing is from Burpee and is a lettuce Vivian, or Romaine. The extra rockwool I used to build up around the stems is turning out to be a good idea, as it is adding the needed support for the leggy stem.
One thing I have noticed as I changed my water yesterday- I am using distilled water, but the pH is 5.3. I didnt add any pH up, and am wondering if this is too acidic for lettuce? Also TDS reading is about 450. Should I go up to 800 or so? Plants look good but want to see if I can 'supercharge' them so to speak. I guess I am getting a little cocky, but want to pust the limits to see what I can produce..... thanks everyone, Loving this hydroponics thing!

    Bookmark   May 15, 2009 at 9:31PM
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