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Brown spots on tomatoes may signal a lack of calcium

Question: I have four tomato plants in two Earth Boxes. These boxes have a water well in the bottom and I fill it with water each morning. The plants are supposed to self water through the bottom of the soil. We used Miracle Grow, Moisture Control Potting Mix and added some fertilizer as directed on the Earth Box instructions. The tomatoes are on the east side of the house. They are shaded from the sun early, and again later in the day. My problem is that about half of the tomatoes have large brown spots on the bottom. A rotten spot. Am I watering them too often? The plants seem to wilt if I do not water them every day. Too much fertilizer? Any suggestions?

Answer: This is blossom end rot. It is a calcium imbalance thought to be caused by uneven watering. Are you sure you kept the reservoir full? I am sure you did, but is it possible that it dried at some point?

I don't think there is a problem with the soil and fertilizer you are using. I am wondering if the soil mix above the tomatoes is too deep. Unlike Pennsylvania, where this was developed, demand for water by plants here can be nearly 50 percent higher than in Eastern states.

This can put a lot of stress on plants if they have to pull water from a reservoir rather than close to the soil surface. If the demand for water is extremely high and the plants can't take up water fast enough, you might get some blossom end rot.

It also is thought to be caused by a lack of calcium, but if you are using tap water (not softened water or distilled water or RO water) there should be plenty of calcium in the water and the soil.

Watch for any midday wilting when it is hot. You might want to purchase a soil moisture meter from a nursery for about $8 and monitor your soil moisture to make sure they are getting enough.

Are you seeing any white deposits on the soil surface? Another problem that could occur is that the water in the reservoir could be wicking to the surface and evaporating, leaving behind salts.

You might also try flushing the soil periodically with water from above if this is possible -- to flush salts. Our tap water carries a very high amount of salts compared to most irrigation water.

Increases in soil salts can cause water stress. Salts in the soil can induce water stress when there is actually quite a bit of water in the soil due to a general salt effect (osmotic). I would flush it just to make sure.

13 years ago. Rating: 0
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