Blossom End Rot - Another Drought Effect

Blossom-end rot on tomato (Creswell)

Anyone who has grown a vegetable garden for any length of time has probably at one point or another experienced the disappointment of reaching for a bright red, juicy tomato off the vine, only to find the bottom of the tomato to be rotten. And this is a year this has been a frequent occurrence for many gardeners. 

The culprit is a non-infectious disorder called blossom-end rot that affects not only tomatoes but also peppers and eggplants. Symptoms of blossom end rot first show up as small, light brown or water soaked spots on the blossom end of the fruit (thus the name). As the fruit ripens, spots enlarge rapidly, forming a dark, sunken, leathery lesion on the bottom of the fruit. Sometimes the lesions will cover the entire bottom half of the fruit. Blossom end rot usually affects the first fruits of the season most severely and many times the symptoms will disappear as the season progresses. While it may appear unappetizing, the un-rotted portion of the fruit is still edible.

Blossom-end rot is caused by a lack of calcium in the fruit. In most cases, this does not mean there is a lack of calcium in the soil. Rather, there are environmental factors that affect the plant’s uptake of calcium.  When the supply of calcium to the fruit does not keep up with its requirements, tissue in the fruit begins to break down. The environmental factors contributing to blossom-end rot include wide fluctuations in soil moisture levels (i.e. letting the plant reach the wilting point before watering), rapid plant growth followed by a prolonged period of dry weather, excessive rainfall which can smother roots, excessive use of nitrogen fertilizer or fresh manure, and root damage. This year's blossom-end rot occurrences most likely are due to soil moisture fluctuations and prolonged drought.

As mentioned early, rarely is the problem due to an actual soil calcium deficiency, so adding calcium to the soil is not usually an effective control method, unless recommended by a soil test. Foliar applications of calcium are also occasionally recommended, however they too are usually ineffective because the plants do not adequately absorb the calcium and get it to where it is needed most. An interesting point regarding blossom-end rot is that it usually affects the first fruits of the season most severely and once the plant's growth and calcium levels get back in balance, the symptoms disappear. So, when gardeners who have applied soil or foliar calcium, or some other home-remedy, see that the symptoms have disappeared, they mistakenly believe the calcium application was effective, when in reality, it was the plant managing the problem itself.    

To reduce the chances of blossom end rot occurring, some preventive steps can be taken. First, maintain a uniform moisture level in the soil - do not let the plants dry out repeatedly. Ideally, plants should receive the equivalent of one inch of water per week via rainfall or irrigation. Second, test soil regularly to maintain proper fertility and pH levels. Next, avoid using fertilizers containing high nitrogen levels or excessive amounts of fresh manure. These materials can cause excessive growth of leaves and stems and inhibit fruit development and production. Finally, do not cultivate deeper than 1 inch within a foot of the plant to avoid root damage.   

Blossom-end rot will always be annoyance for vegetable gardeners but with a few simple preventive steps, its effect on production can be greatly reduced.