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One of my tomato plants (Better Boys if that matters) has a few leaves that have started yellowing on the lower branches. Not sure if they aren't getting enough water, or if they are diseased or what.

What is causing this? If it's a disease how can I prevent it from spreading to the rest of my plants?

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Did you tomato plant survive & go onto produce ok? Or did you have to destroy the plant (eg Due to "blight")? – Mike Perry Sep 6 '11 at 23:44
Well, most of my garden tomato crop died. I've got 2 or three plants left that aren't producing well. I've got a couple of heirlooms planted in the garden that are doing ok and starting to produce. I also have a couple of potted tomato plants, one from a cutting of one of the better boys and 2 more heirlooms. The one from the cutting is flowering, but not fruiting...the other two aren't ready yet. – wax eagle Sep 7 '11 at 0:27
Isn't it getting very late in the season where you are, or should you still have time to set fruit & get a crop? – Mike Perry Sep 7 '11 at 0:34
hoping I still have time. I'm in a moderately elevated area of N. GA (2-3k feet up). Hopefully I have a month to a month and a half before first first frost. We usually get a frost in mid October or so, but if we're luck it will hold off until November... – wax eagle Sep 7 '11 at 0:41

3 Answers 3

up vote 11 down vote accepted

You probably can pinch the lower branches off, and actually help the growth of the plant. Your plant can grow pretty big (4 feet) so to encourage tall growth (and keep the leaves away from the dirt, which probably caused the yellowing) pull them out.

If it goes on, pull the plant out (don't compost it) and be thankful it is early in the year.

It's probably not the water, unless you're watering directly on top of the plant and causing them to get muddy. Try watering at the base and making a little dirt moat around the plant so that the water goes into the ground and the roots have to grow down to get it.

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Hi, i have the same problem (my tomato plants are indoors in pots). I transplanted them today into 5L pots, previous pots were full of roots, i thought the yellowing was related to that. Is it? What do you mean by "pull the plant out"? – Benjamin Jun 11 '11 at 19:37
Just make sure if you pinch off the lower branches you do it when it is dry, otherwise you can invite infection. – nuttzman Jun 12 '11 at 12:15
@benjamin, I mean yank them out and throw them in the trash, do not compost, do not collect 200 blights. Three years ago So. Wisco got the worst tomato blight we've seen in a long time, that year I burned my tomatoes where they stood, got nearly nothing out of a whole years work. Probably could have avoided it if I'd have pulled the infected plants out first. – Peter Turner Jun 13 '11 at 17:39
Some if my plants get an overall yellow tint: see picture. Others get yellow tips at the top now: see picture. Does it give more clue as to what can be the cause really? – Benjamin Jun 16 '11 at 11:16
@Benjamin, I've never grown tomatoes indoors in pots, if it's not a disease it is certainly becoming susceptible to disease. Is there any chance it's not getting enough sunlight? Also, it looks like you've got 5 tomato plants growing within an inch of each other, is that normal for container gardening? I'd think one would be the most you could do. – Peter Turner Jun 16 '11 at 13:15

Yellowing of the lower leaves can be caused by a few different things (and these are different things than if it starts with the upper leaves). How the leaves are yellowing can give you clues as to what is wrong.

If the whole leaf is yellowing, nitrogen deficiency is often the cause. If just the edges of the lower leaves are yellowing, potassium deficiency is often the cause. Too much potassium may cause lower leaf yellowing because it can inhibit magnesium uptake. Magnesium deficiency can cause yellowing of older leaves, but the veins may remain green.

Too much boron may also make the edges of the leaves yellow.

Large amounts of calcium may inhibit potassium, and too much magnesium will do the same in at least water plants. I guess this explains why giving my plants basalt rockdust seemed to give them potassium deficiency, with the edges of the leaves yellowing (rockdust is high in calcium).

I've heard a rumor that too much nitrogen inhibits potassium uptake, and perhaps vice versa (so, if true, too much of either can potentially cause some form of yellowing). I have not, however, found a reliable source to verify either of these claims. My personal experience makes the rumor seem as if it might be true, but not enough to be certain. I used to propagate this rumor, thinking it was something a lot of people knew (because I heard it more than once), but now that I've actually looked into it more, it may just be a rumor, after all. Too much nitrogen may inhibit roots, however (and potassium is supposed to help the roots), and, again, too much potassium can cause yellowing due to inhibiting magnesium.

In my experience, if you have lots of plants close together in a warm, humid environment, this may also cause yellowing of lower leaves, particularly the edges (probably due to some fungus in my area). It looks like potassium deficiency, but I've had it happen on plants that I had already given plenty of potassium previously. I'm not sure why this happens, but yellow discolored circles or patches, or bumps on the leaves can result, too (and usually do instead of it mimicking potassium deficiency). Giving the plants a cooler, dryer environment with more space has easily fixed this problem, for me. Lots of light is also important, but not as important as temperature, dryness and space. This happens much less on plants with enough potassium, even though it still may happen.

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This could also simply be a Nitrogen deficiency. The plant will transfer Nitrogen from the lower, older leaves up to the upper, newer ones if it doesn't have enough available Nitrogen in the soil. Feeding with fish emulsion (There are a few brands, and what your local store has will probably depend on what region you're in: My local Home Depot carries it). would give it an immediate boost, or you could use something else with a medium to high N number on the fertilizer bag.

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could you provide info or a link on fish emultion? thanks. – Benjamin Jun 11 '11 at 20:22
If you just transplanted, the new soil will probably provide enough Nitrogen for at least a couple of weeks without you needing to supplement. – baka Jun 11 '11 at 20:25

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