Tuesday, May 24, 2011

FAQ: The bottoms of my tomatoes are rotting. What is the problem?

The bottoms of my tomatoes are rotting what is the problem? What can I do about it?

The disease is called "blossom end rot" and it is caused by calcium deficiency in the fruit. Calcium strengthens the cell structure. When there is insufficient calcium, the cell walls are weakened and are prone to burst. It starts in the blossom end, because that is the weakest point in the fruit. Then it spreads because the surrounding cells are stressed more and burst.

The problem is essentially an environmental one, beginning perhaps with insufficient calcium in the soil. But even if there is enough soil calcium, other factors can prevent enough of it from reaching the fruit. Water transports the calcium, so if there is a lack of water, the calcium is not carried where it is needed. If the soil is dry, there will not be enough water. If air temperature is very hot, there may not be enough water in the plant itself. Dry soil and hot temperatures are usually coincidental, compounding the problem.

To help prevent blossom end rot, test your soil before planting. You can take a sample to your nearby Cooperative Extension Office for analysis. The site should be in full sun. The soil should be high in organic matter and well-drained. Soil pH should be 6.5. If it is lower than that, add lime according to the soil analysis recommendations. Compost is always an appropriate soil amendment.

For good measure, add 1/2 cup of pelletized dolomite lime and 1/4 cup of 10-10-10 fertilizer to each planting hole before planting. Mix well. Do not allow fertilizer to come into direct contact with the plants. Water well after planting. Cover soil with mulch to 3 inches deep in order to preserve soil moisture. Provide 1-1/2 inches to 2 inches of water per week.

For added protection, spray your tomatoes weekly with calcium chloride when the blossoms are forming and fruits are small. This is usually done during late spring and early summer. Calcium chloride is available at garden centers.

Tomato varieties resistant to blossom end rot have been developed recently. Remember that rot resistant doesn't mean rot proof, but every advantage helps.

If you did not add lime to your soil before planting your tomatoes, it is too late to add it when blossom end rot appears. At that point, calcium chloride spray and adequate irrigation are your only remedies.

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