You are going to have to help us help you. We need a lot more information. Where about are you located, the environmental conditions and how you are growing them, how you are watering, how much you are watering, any fertilizers used...

Rodney

Agree. Your photo could have numerous causes so details are needed. For example, have you checked it thoroughly for pests? I appears that there may be some aphids in the photo but can't tell for sure.

Dave

Thank you. It is an heirloom black prince. Growing in Virginia. I have not sprayed or treated for any pests or disease. They were planted on Mother's Day. Weather has been normal (80-90 degrees). Rain is normal, no drought. I water 2x per week -- I planted a 5 gallon trashcan next to this plant and two others, buried 1/3 of the can, with holes drilled in bottom, to provide slow subsurface irrigation. I feed 1x per week with compost and heirloom tomato fertilizer added to the irrigation can.

What is the sun exposure like? How many hours of direct sunlight?

And... what exactly makes that fertilizer for heirlooms? I can't think of anything that could make a fertilizer specialized in that way. Of course you should use whatever you're comfortable with, but many of us are cautious of such labeling. It's usually a way of charging more money for what's usually an inexpensive product.

How large is the plant? Approx what percentage of the foliage is affected? Is it a lot of the lower foliage or just these leaves in the picture? Do you have a photo of leaves that are affected with lesions or the starting of yellowing but not practically dead like these leaves?

Whenever I see anything planted close to a building I suspect water issues. If the plants were stressed with dry soil, even once in their life, the lowest leaves are likely to yellow as those are. Likely much of the tank water drains away rapidly along the foundation and little is readily available for plants. In the future I suggest that all plants be a few feet outside of any foundation.

"I planted a 5 gallon trashcan next to this plant and two others, buried 1/3 of the can, with holes drilled in bottom, to provide slow subsurface irrigation. I feed 1x per week with compost and heirloom tomato fertilizer added to the irrigation can."

In addition to all the other points made about lack of any nutrients and water, I will add that set-ups such as you describe are very prone to plugging up the holes and restricting water. Plus compost left to stand in such an environments can easily turn anaerobic.

Such an approach isn't nearly as ideal as it may sound.

Dave