This time of year, I get lots of questions like, “Randy, what’s happening to my tomatoes? Is this a disease or an insect problem? And how can I fix it?”
It’s affectionately known as blossom-end rot, and its cause is neither a disease nor a pest. It’s a cultural care problem - a physiological issue.
It’s actually the sign of a calcium deficiency in the soil. And that makes the problem very fixable. And, more good news - any vegetable suffering from it is still edible once the rotted part is cut away.
While blossom-end rot seems to most commonly target tomatoes, it is showing up this year on a variety of cucurbit crops, such squash, zucchini and cucumbers. You know you have it when a dry, black area develops at the base of green or red fruit.
On tomatoes, it normally happens on medium to large sized varieties. The issue can appear at any time in fruit development, but it most commonly pops up when they are one-third to one-half grown. The initial symptoms are water-soaked spots at the blossom end of the fruit. They later enlarge and become black. Secondary infections by other decay-causing organisms usually follow.
Okay, so how do you fix the calcium deficiency? First, watering needs to be extremely consistent - wide fluctuation in moisture is the first cause. Too much, then not enough, results in calcium being leached from the soil. But widely available calcium products, such as calcium chloride, can help replenish it. We’ve also discovered that using trace mineral packages such as Azomite can help.
If you think your watering is consistent, and you believe your soil has the appropriate trace minerals, other practices that can cause blossom-end rot include root pruning and excessive nitrogen fertilization. Stopping those can resolve the situation as well.
PHOTOS: Tomatoes - Randy Lemmon; Squash - Gerald Holmes, California Polytechnic State University