I can’t figure out my the leaves on my tomatoes on turning yellow The plants are in a pretty sunny part of my yard, they are in pots, with potting soil. I tried cutting off the yellow leaves, but then more appeared.
Thank-you for contacting Toronto Master Gardeners with your question. There are several conditions and problems with tomatoes that have a symptom of yellow leaves. It can be difficult to identify the particular culprit in a situation. Sometimes yellow leaves are caused by a disease or pest, but other times it can be a case of under or over-watering, or a nutritional deficit.
Pests and diseases can target tomato plants. You can usually see the pests and both situations often result in other symptoms as well as yellowing leaves (holes in the leaves, brown spots, withering of the whole plant).
In your circumstances, I am suspecting a problem with either watering or nutrients. The small pots you have your plants in make it difficult to ensure proper watering and tomatoes are picky in their water requirements. The soil must not be allowed to dry out, but equally, or perhaps more deadly to tomato plants is standing water or continually soggy situations.
It is also possible that your plants have exhausted the nutrients available in their small pots. They are heavy feeders. Nitrogen, magnesium, iron, potassium deficiencies are all common problems with tomato plants. A balanced fertilizer could help in that case.
Good luck with your tomato crop!