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Blossom End Rot

Blossom end rot on a developing tomato.

Unaffected areas of ripened fruit are still edible.

Tuesday, July 5 | Gardening Info

Blossom end rot is one of the most common problems encountered in tomatoes and other fruits.  As the fruit develops, a small, dark spot appears on the blossom end (usually the bottom).  The spot eventually turns into a large, black lesion that can consume most of the fruit.


BER is caused by a shortage of calcium in the plant.  Calcium is required for proper development in plant tissues.  In rapidly growing plants, the root system sometimes has difficulty maintaining an adequate supply of calcium to the fruit causing the new tissue to break down and rot.  Several environmental factors can cause BER:

Not enough calcium present in soil:
Be sure to amend soils with quality compost prior to planting and feed with a vegetable-specific fertilizer like Tomato Maker.

Too much water / too little water:
Consistent over watering or under watering can lead to a plant with a weak root system.  Weak roots can’t effectively supply enough nutrients to the fruit.

Calcium unavailable:  Low soil pH caused by excessive ammonia in the soil can reduce the plant’s ability to absorb the calcium that is present in the soil.  Acidic soils should be amended with horticultural lime prior to planting.

Plant growing too fast:
Plants that are fed too much nitrogen or plants that are grown in ‘tropical’ conditions with lots of water, sun and warmth can actually set and develop more fruit than the roots can handle.  Be sure to fertilize regularly with a vegetable specific fertilizer with a small 1st number (nitrogen) and a higher 2nd number (phosphorus).

Physical Root Damage:  Soil borne pests like grubs and moles or cultivating too deep or too close to the plant can damage its roots and lead to nutrient uptake issues.



Proper nutrition is the key to prevention of BER.  Amend your soil with compost prior to planting, consider applying lime to acid soils, and use a vegetable specific fertilizer regularly throughout the growing season.  Place mulch around the base of your plants to reduce water stress during periods of drought.  Consider shading and sheltering your plants during periods of extreme wind and heat to further reduce water stress. 
Since BER is a physiological problem, it will not spread from fruit to fruit or from plant to plant.  Don’t confuse it with a blight.  Once the problem starts, little can be done to save affected fruit.  It may prove beneficial to remove affected fruit to reduce the nutritional demands on the plant.  It can also be beneficial to spray calcium solutions (like Bonide’s Rot Stop) on fruits not yet affected by rot.  BER frequently remedies itself as the season wears on with the application of proper fertilizer, natural hardening and maturing of the plant, and moderating temperatures in the later summer / early fall.