Ask a Question forum: Tomato seedlings

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Name: Bruce
NW CT (Zone 6a)
Composter Permaculture Region: Northeast US Roses
Bmyoung
Apr 7, 2017 12:46 PM CST
My tomato seedlings (now in 4" peat pots) have yellowing in their lower leaves... I've got them in my basement on grow mats under led grow lights. . Stocky and nice growth, but in the last two weeks have developed this yellowing...

I've been careful not to overwater.... Maybe too careful?

Not enough food?

Any thoughts appreciated!

Thanks,
Bruce
Name: Cindy
Hobart, IN zone 5
aka CindyMzone5
Celebrating Gardening: 2015 Plant Identifier
Shadegardener
Apr 7, 2017 3:51 PM CST
When you say "grow mats", what do you mean? For heat or for moisture?
Only when the last tree has died and the last river has been poisoned and the last fish has been caught will we realize that we can't eat money. Cree proverb
Name: Daisy I
Reno, Nv (Zone 6b)
Not all who wander are lost
Garden Sages Plant Identifier
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DaisyI
Apr 7, 2017 5:10 PM CST
Did you use seedling soil to start your little tomatoes? If so, time to add a little fertilizer. Mix it at 1/4 the recommended strength. You will see results in just a day or so.
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and proclaiming...."WOW What a Ride!!" -Mark Frost

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Name: Elaine
Sarasota, Fl
The one constant in life is change
Cat Lover Master Gardener: Florida Tropicals Multi-Region Gardener Vegetable Grower Region: Florida
Herbs Orchids Birds Garden Ideas: Level 2 Garden Sages Celebrating Gardening: 2015
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dyzzypyxxy
Apr 7, 2017 5:12 PM CST
H Bruce, a picture of the plants would be most helpful if you can post one?

If they're in 4in. pots now, you need to be fertilizing them regularly. I'd use 1/2 strength soluble fert once a week.

How long are you giving them light? They need at least 12hr. per day. Any way you can bring them upstairs to a sunny window for more light?

Have you checked the backs of the leaves for spider mites or whiteflies? They could be causing the leaves to look pale, too. A mild soapy water spray (1/2tsp. dish soap to a quart of water) will take care of them if you find any.
Elaine

"Success is stumbling from failure to failure with no loss of enthusiasm." –Winston Churchill
Name: Bruce
NW CT (Zone 6a)
Composter Permaculture Region: Northeast US Roses
Bmyoung
Apr 8, 2017 4:14 AM CST
Its almost more that they are 'purpling'... which I read somewhere isn't the worst thing for seedlings under lights. Here are some images and yes, I meant heat mats.
Thumb of 2017-04-08/Bmyoung/b1d837
Thumb of 2017-04-08/Bmyoung/15be38

Name: Sally
central Maryland
Seriously addicted to kettle chips.
Charter ATP Member Native Plants and Wildflowers Region: Mid-Atlantic Composter Region: Maryland Birds
Cat Lover Dog Lover Region: United States of America
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sallyg
Apr 8, 2017 5:54 AM CST
Once they sprout, I think the heat mat is not needed anymore (but don't think that is causing a problem necessarily)
..come into the peace of wild things..-Wendell Berry
Life is a buffet (anon)
Eastern Tennessee (Zone 7a)
Nominix
Apr 8, 2017 7:35 AM CST
The Rusted Garden - https://www.youtube.com/channe...

He has an entire series devoted to tomatoes from seed to harvest. In one video of that series he talks about purpling of the stem. Its worth a watch.
Name: Elaine
Sarasota, Fl
The one constant in life is change
Cat Lover Master Gardener: Florida Tropicals Multi-Region Gardener Vegetable Grower Region: Florida
Herbs Orchids Birds Garden Ideas: Level 2 Garden Sages Celebrating Gardening: 2015
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dyzzypyxxy
Apr 8, 2017 10:49 AM CST
I agree with Sally, you don't need the heat mats any more unless it's really cold in your basement. Think I'd try a douse of Epsom salts on those guys. Maybe 2tsp. to a gallon of water. Red or purplish color is often an indicator of magnesium deficiency, and this gives a quick shot of magnesium to the plants. Tomatoes love magnesium. See if this works, and if so, just add a tsp. of Epsom salts to your fertilizer solution so they get a little bit each week. The purple color should begin to fade within a few days if it's working. In any case it can't hurt.

Do you know what the pH of your water is, btw? Hard water (with a high pH) can "bind" up certain minerals that your plants need - like magnesium - and prevent the plants from being able to absorb and use them.

They don't look like you're overwatering, in fact the soil surface looks pretty dry. The mottled look of the leaves might indicate there was some sort of insect activity, but I can't see anything in your picture. Try looking with a magnifying glass - spider mites are very tiny. Or if you run your finger along the underside of a leaf and it comes away with a little bit of reddish-orange staining that also indicates spider mites.

I'd give them the soapy water treatment in any case. It can't hurt and might stop an infestation if it's just in the early stages. Be sure to spray up under the leaves, the stems and the soil surface, then rinse the soap off with a spray of plain water later. It can make the leaves hyper-sensitive to light.
Elaine

"Success is stumbling from failure to failure with no loss of enthusiasm." –Winston Churchill

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