Yellowing seedlings

[snappybob]

My tomato seedling which have been growing since I planted in Mid January are looking a little yellowish. They have been potted up into 16 oz cups and are getting pretty big. I think it might be time for a little feeding. I am planning on giving them some diluted fish emulsion to tide them over until I can get them into the ground in a few weeks. I normaly dilute my fish emulsion by 1 table spoon to 1 gal of water. I was thinking about diluting it for my seedlings to 1/2 table spoon to 1 gal water. Does this sound about right?

[bryanccfshr]

That should be good. Maybe a little less. You can alsways add more if they don't respond but perhaps 1/4th strength and watch for a response and repeat if the response in a couple of days is not apparent.

[bcday]

I think I would make it even less than that. If 1 tbsp. per gallon what is recommended on the label for outdoor plants in the ground, usually the dosage for mature plants in pots is a lot lower, like 1 teaspoon / gallon, and for young seedlings I'd cut that again by half or more. It doesn't take much to burn the roots of seedlings. I use 1/4 teaspoon per gallon, and as mentioned above you can re-apply at that dosage if needed without harming the plant. 1/2 tablespoon per gallon sounds pretty strong for seedlings in pots.

You can also get quick results by using a fertilizer that is safe for foliar feeding and spraying it in the leaves. But you definitely don't want to make it too strong then either.

Are you sure the yellowing is due to lack of nutrients? What kind of mix are the seedlings growing in?

[snappybob]

When I potted up to the 16 oz cups I used Scott's potting soil with 25% compost added.

[Ruth_10]

Also, are they under lights or out-of-doors getting some direct or indirect sunlight? If indoors under lights, they might not be getting enough light if the plants are getting large or the lighting setup isn't optimal for larger plants.

[bcday]

You don't say how big the seedlings are, but unless they're really huge to the point that the cups tip over from being top-heavy, I don't think the soil in the cups has run out of nutrients.

It may be that you're watering the seedlings too much. The soil shouldn't be constantly soaking wet. Roots need air as much as they need water.

If you used potting soil instead of a lightweight peat-based potting mix, it's also possible that the soil in the cups is too dense and is staying wet too long between waterings.

Just as an experiment, if one of the seedlings is an extra one that you don't mind repotting, knock it out of the cup and see what the soil looks like. If the soil is wet and heavy even though it hasn't been watered recently, that might be your problem. And if it isn't completely filled with roots, it hasn't run out of nutrients so you won't need to fertilize.

[Granny]

Originally Posted by bcday

You don't say how big the seedlings are, but unless they're really huge to the point that the cups tip over from being top-heavy, I don't think the soil in the cups has run out of nutrients.

It may be that you're watering the seedlings too much. The soil shouldn't be constantly soaking wet. Roots need air as much as they need water.

If you used potting soil instead of a lightweight peat-based potting mix, it's also possible that the soil in the cups is too dense and is staying wet too long between waterings.

Just as an experiment, if one of the seedlings is an extra one that you don't mind repotting, knock it out of the cup and see what the soil looks like. If the soil is wet and heavy even though it hasn't been watered recently, that might be your problem. And if it isn't completely filled with roots, it hasn't run out of nutrients so you won't need to fertilize.

One thing I discovered about the plastic cups that I used last year was that just poking holes in the bottom did not provide enough drainage, so the soil stayed much too wet. I ended up taking a pair of scissors and snipping 1/2 inch wide triangular pieces out of the edge of the cup where the side meets the bottom in about three places. Made a huge difference.