Are they still developing yellowed leaves?
As I mentioned elsewhere, my extremely pot-bound tomatillo starts were developing bright yellow lowest leaves like you described for the potatoes. I took some of them off but left a few in place when I planted them out to see what they would do — I’m curious if those leaves will be able to recover after settling in/adverse conditions are reversed.
Since they were pot bound, lack of nutrients and water that Gary350 mentioned are definite possibilities. But it’s also possible they got waterlogged from overcompensating and/or soaking in rainwater all night.
I was thinking that since you mentioned companioning them with corn, that if the corn had reached the next phase of growth when they need extra nitrogen -and at the recommended schedule for side dressing- they might have suddenly sucked up all the available nutrients?
If the yellows leaves are not functional/lost cause, then I think you might as well remove them and hill up or mulch the stems higher like jal_ut suggested. You could just pile leaves or straw, too.
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