Blossom End Rot on Tomatoes
It's finally here! Your first red tomato. You reach in, twist it off the vine and have a look. And there it is - a big black spot on the bottom of the tomato.
The problem is blossom end rot. It’s caused by a lack of calcium in the soil. Now don't reach for the fertilizer, most soils have plenty of calcium. If in doubt, have a soil test before spending money on something you may not need. Root damage or moisture imbalances are usually the problem. They prevent the plants from absorbing the calcium from the soil.
The first flush of tomatoes is usually all that is affected. The plants seem to adjust and correct the problem.
Prevent the problem by keeping the soil evenly moist throughout the summer. Proper watering and mulch can help.
Avoid root damage when staking and cultivating your garden. And, don’t use ammonium forms of nitrogen prior to or during fruit set.
The good news. It’s safe to eat the firm red portion of the tomato.
A bit more information: Check the soil moisture in container-grown tomatoes daily. Fluctuations in soil moisture are greater in containers than in-ground plantings. That means a greater risk of blossom end rot. Water thoroughly whenever the soil is slightly moist like the consistency of a damp sponge. Most planters need to be watered thoroughly every day. Some even twice a day. Keep in mind the smaller the container and the higher the temperature the more often you need to water.
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