QUESTION: Should I cut off yellow leaves on tomato plants?
ANSWER: Once your tomato plants are around 12 to 18 inches tall, you may notice that some of the leaves below the first set of flowers have begun to turn yellow or die. With all varieties of tomatoes, you may remove the dead or yellowing foliage as long as it is below this first set of flowers.
With determinate varieties of tomatoes, there is nothing to gain from removing dead or yellowing leaves, or “suckers,” that grow any higher on the plant. (You may choose to remove the “suckers” that grow from where a branch meets the main stem on determinate tomatoes as long as they aren’t higher than the first set of flowers. On indeterminate tomatoes, you may remove all suckers as long as they are not so large that doing so would leave a damaging wound on your plant.)
Indeterminate varieties of tomatoes may benefit from removing dead or yellowing leaves at all heights and more pruning overall than determinate varieties. That’s because determinate tomato plants will flower and set fruit once, so there is a set number of potential tomatoes that can’t be altered much by pruning. With indeterminate varieties that will bloom and set fruit more than once in a season, the benefits of pruning are greater.