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Blossom End Rot: Characteristics, Causes, and Solutions to Protect Tomatoes and Vegetables

© Vic Ferri

Blossom end rot is one of the most common problems when growing tomatoes. Brownish-black leathery patches appear on the bottom of your tomatoes. It is also common on peppers, squash, eggplant, and melons. 

Causes of Blossom End Rot

Blossom end rot is not a disease, but a lack of calcium in the developing fruit. The calcium-deprived tissue breaks down resulting in the characteristic symptoms.

Some people assume this means that their garden soil must be deficient in calcium. However, the real problem is that the plant is unable to absorb the calcium that is in your soildue to  uneven supply of water.

It is essential to keep the soil consistently moist rather than let the soil completely dry out and then water fully. This extreme fluctuation is almost a surefire way to induce blossom end rot.

Too much nitrogen in the soil can also cause rot. In this case, a handful of lime around the base of each plant might help. It is important to cut back on your fertilizing or switch to a brand that has a low nitrogen and high phosphorous to high potassium ratio.

Other conditions that may bring about blossom end rot are weather-related: extreme changes from hot to cool temperatures, stress from drought, and heavy rains after a dry spell.

Solutions to Prevent or Reduce Blossom End Rot

• To help maintain even soil moisture, mulch your plants. However, even with mulches weekly watering will be necessary if there is no rain.
• Choose a low nitrogen fertilizer in which the nitrogen is in nitrate form rather than one that releases nitrogen in the ammonium form. Excess ammonium ions reduce calcium uptake.
• Do not cultivate too deeply. Try not to disturb the soil around the base of the plant. Deep hoeing or transplanting can damage feeder roots and thereby reduce calcium uptake.
• Make sure your tomatoes are planted in well-drained soil. Soggy soil causes roots to smother leading to reduced calcium uptake.
• Plant your tomatoes in a soil rich with organic matter. This also will help prevent the soil from drying out too quickly.
• Spraying the leaves weekly with a calcium nitrate solution can significantly reduce blossom end rot.

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