tomato leaves yellowing

Does anyone know why the leaves on some of my tomato plants turn yellow and then die? They are in
separate pots precisely because last year, when they were all together in the same garden, they all
got yellow leaves and eventually all the leaves died. This has happened for the past several years.
I am lucky this year that only 2 out of 22 are exhibiting this so far. Each of the 22 are a different
heirloom variety that I grew from seed. Oops, I lied. The only one I purchased at a gardencenter, the
Brandywine, was the first to go. But a couple of others are exhibiting now, and they are not beside
each other.

Some tomato plants produce fruit endlessly until frost. Some produce a single set (harvest may last 3 weeks or so) and then the main plant dies. I think Brandywine is in that second category.

Mine normally start to show discolouration like yellowing when the plants have fruited there socks off and are tired out, OR if there has been a lack of water, but I normally remove the leaves in question and examine them under Microscope to check for any bugs, disease etc, etc, if none spotted, then give a feed, water and keep a close eye on them until your growing season is over. This year has been an exceptional good year for Tomato's here in UK as we had a good long spell of hot sunny weather, but other things like peppers etc were a total flop for me and I heard other growers say the same, the peppers were very small, miss shaped and a good few rotted before ripe, so thats gardening for you eh, hope you can get through to the end of your growing season OK without too much troubles, good luck WeeNel.

Hi - I sell organic seeds for a living here in Queensland Oz

1 - You are overwatering
2 - The plants are screaming out for potassium and this is probably the cause - can you obtain organic Rose fertilisers where you are? rose fertiliser has the highest rate of potassium than any other fertiliser - you don't need much just a small amount - this isn't my tip, I was told this by an old gentleman years ago (rest his soul) and I will be forever grateful to him and his gardening tips and I pass the tips on to whoever will listen lolol. Sandy aka bluebell33 :)

Welp, since you posted in July I doubt any of us can help you now, Cyn, but for future reference...

You mentioned your plants were in pots. The yellowing could be from waterlogged soil or, as bluebell mentioned, overwatering. It could also be from lack of nitrogen, especially if the lower leaves are yellowing and the upper leaves are not. If I'd seen this post back in July I would've asked for more info regarding your growing conditions. Sorry.

As for potassium deficiency, NOT. That tends to give leaves a blue-ish/green color, not yellow, with the only exception being a bit of chlorosis between the veins of the leaves. Usually you will see the edges of the leaves scorched if potassium is at fault.

By the way, Cyn, how'd your plants do the rest of the summer? Didja get any harvest or resolve your problem?

Bluebell, I see you are new here. WELCOME to DG! Hope all is going well down in Oz.

Shoe

the yellowing is usually a plant disease called " early blight". it is from excess moisture and usually occurs in the bottom of tomato plants where the sun light can not reach. other plants related to tomatoes such as potatoes get this as well. it spreads very easily. pull everything that is yellow off and get it out of there. your plants will survive.

James