How to avoid blossom end rot on your homegrown tomatoes

Every year people ask about blossom end rot—a dark leathery spot on the bottom of the tomato. Your plant will continue to bloom and set fruit until the end of the season. It’s pretty common and especially so with tomato plants growing in containers. It’s most likely caused by a calcium deficiency.

The disease is especially prevalent when rapidly growing plants are exposed suddenly to a period of drought. When the roots fail to obtain enough calcium that is transported by the water up to the rapidly developing fruits, the fruits become rotted on the bottoms.

In containers, use a potting soil/mix containing ample sphagnum peat moss. This helps reduce the problem. Like a sponge, sphagnum peat moss absorbs and holds up to 20 times its own weight in water. The ingredient coir also helps; coir can hold up to 7 to 8 times its weight in water. Remember, the soil contains the calcium for the roots to absorb and then water transports calcium up to the growing plant.

Like a sponge, potting soils/mixes with sphagnum peat moss and/or coir keep a lot of water and moisture containing calcium around the roots. Potting soils/mixes without sphagnum peat moss drain and dry out more quickly. Little or no water means dry soil and little or no calcium transported up to the tomato plant. Also, adding a mulch such as a layer of straw on top helps keep the potting mix/soil moist and reduce water evaporation. 

In general, there does not seem to be any easy fix for blossom end rot. Keep your tomato garden soil/potting mix consistently moist with regular deep, thorough watering. Don’t let your Self-Watering Container run dry and don’t let your tomato plant “droop” from lack of water. I generally remove and toss the affected fruit. If it’s excessive, I’ll pull the plant and start with a new one.

I have never heard of blossom end rot in cherry tomatoes. Blossom end rot occurs more often with tomatoes grow in containers as compared to backyard/raised bed type planting. It’s the bigger size tomatoes that get blossom end rot and we all have experienced it and I don’t know of a sure fire fix or prevention. Some people swear that by using crushed egg shells in the soil around the plant cures the problem.

You are welcome to share this information with others—clubs—perhaps share this with your general membership to include those that could not attend the lecture, family, friends, etc. 

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Dave Freed /  the Tomato Guy