The Q&A Archives: tomato leaf discoloration

Question: we have tomatoes in earthboxes. They are huge.. the bottom leaves are developing yellow mottling between the green veins of the leaf.
The other problem we have specific to the earthbox grown tomatoes is blossom end rot on the tomatoes. Is there a soil amendment that will stop this before it happens? I don't want to spray them.

Answer: Blossom end rot is a physiological condition caused by a lack of calcium at the growing tip of the fruit. While your soil may have adequate calcium, fluctuations in soil moisture content from dry to wet really increase the incidence of blossom end rot. It is especially bad on the early fruit each summer and in sandy soils. The damage occurs as cells die at the tip of the fruit. In time (and as the fruit grows) the spots enlarge and turn black. So, by the time you see it, the damage actually has already occurred some time back. Remedies include: having a soil test to make sure calcium levels are adequate, adding organic matter to a sandy soil to increase its moisture holding capacity, keeping plants evenly moist, especially during the development of the first fruits (mulch helps maintain soil moisture), and spraying plants with a Blossom End Rot spray (contains calcium) which can usually be purchased from your local garden center. Usually the cultural practices will control the problem without the need for spraying. The tomatoes are still edible. Just cut away the affected portion. It's natural for the lowest, oldest leaves on your tomato plants to yellow and die. As long as you are getting new growth at the top of the plant, there's nothing you need to do. I usually pinch off the yellowing leaves just to make the plants look better. Good luck with your tomatoes.

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