Gardening with Gary

Gardening Advice from an Expert

Yellowing Leaves

Q. Once the leaves on a plant begin to turn yellow, due to, say, overwatering or underfertilizing, will the same leaves ever green up again? Or should you just pluck them off?

A. Good question! I've never seen one turn green once it's become yellow. but it seems like it should, since the circulation system is still in place.

Yellowing is caused by:
low nitrogen
low light
too much or little water
low iron
low or high pH

What we studied is that once a leaf turns yellow, it rarely will green up. In some cases it will, with an application of high nitrogen food. I have seen bad cases of iron deficiency and giving the plant liquid iron has greened up the foliage from what it was suffering, called chlorosis.

The cells shut down once the nitrogen is not there to assist making chlorophyll. Studies have been done and I am sure are still, but what we have available commercially to apply to our indoor/outdoor plants, there is not one to rectify the yellowing due to deficiency or a watering problem. But, some times a plant is lacking a 'minor element' and that is why it is important to use a fertilizer marked with the various elements inside.

I remove all yellow leaves off my violets. I have never seen an outer one green up, but I sure have seen the tiny yellow ones inside green up once I applied high nitrogen. Many times, the soil mix being used is locking the food in, so it is not readily available to the plant. Too low or high pH has a similar effect, so if you are seeing this a lot, out of the ordinary, I would test the soil and adjust to the more neutral 7.0 pH.