I would carefully dig up the yellow plant with the NEW yellow leaves and examine the roots and basal plate for root maggots. The larvae of a fly, they could be on only one plant, but will move to others after it dies.

The failure of new growth like that indicates a serious root issue.

Hi planatus,

I checked the roots out of one these yellowing onions and they looked good, actually much better than I expected. Attached is a photo showing the roots. I didn't see any signs of root maggots, nor the roots or the basal plate showed any signs of rot. Actually, besides the yellowing, these plants look perfect.

Thanks,
J Silverman

I tried looking at the roots up close but could not get a clear focus. There is a question about the short, perhaps dry roots in the center, just beneath the crown. Why are they not long and white? I think something cropped them, or they ran into something in the soil they did not like. Stuff happens.

I fill gaps in onion plantings with lettuce or other leafy greens and pull them young. The greens shade the onion roots without crowding them.

This post was edited by planatus on Fri, Apr 25, 14 at 8:26