Tomato Patch: An Ugly Problem

Early signs of blossom-end rot on Super Marzano fruit

“What’s this?” asked my friend Karnik, holding out a small red tomato and pointing to its black tip. “Is it some kind of disease?”

“No, it’s blossom-end rot,” I said. “But it’s rare on small, cherry tomatoes like that.”

“This isn’t a cherry. This is a Roma,” he replied.

“It’s not a disease,” I said. “It’s caused by calcium deficiency.”

Photo 1 shows you what blossom-end rot might look like when you first spot it in your Tomato Patch. The young fruit in the photo are Super Marzano, a Roma-type tomato I’m trying for the first time this year. I haven’t counted the number of defective fruit that I’ve thrown away, but I estimate I’ve lost 15%.

More advanced stage of "rot"

Here’s what the Plant Diagnostics tab at the University of Maryland Extension’s Home and Garden Information Center says about the problem: “Blossom-end rot is a common nutritional disorder of tomato, pepper, eggplant, pumpkin, squash and watermelon that is caused by a shortage of calcium in enlarging fruits. Calcium is taken up constantly by plant roots as a dissolved nutrient and travels first to the growing points—new leaves and shoots. Fruits may experience a shortage of calcium if water becomes less available to plant roots (drought).

“This nutritional disorder typically occurs when plants are growing rapidly and the first fruits are developing,” the University of Maryland Extension resource continues. “As fruit cells breakdown due to a lack of calcium, dark blemishes appear on the blossom-end of affected fruits. These may enlarge until the entire bottom of the fruit becomes dark, shrunken and leathery. Factors that encourage blossom-end rot include low soil pH and low levels of calcium, inconsistent watering, shallow watering or droughty conditions, and excessive use of nitrogen fertilizers. Symptoms are rarely seen in cherry tomatoes and are most often seen in large plum or paste-type tomato cultivars and long pepper fruits.”

All sizes of fruit may be affected

I will add a symptom that often helps me spot young fruit with blossom-end rot: premature coloring of a fruit while other fruit on the same truss (fruiting stem) remain green and continue to grow.

How can gardeners prevent blossom-end rot?

The Extension suggests the following steps: “(1) Maintain soil pH in the 6.3-6.8 range. (2) Mix in a handful of ground limestone with the soil from each planting hole prior to transplanting. (3) Keep plants well mulched and watered through the growing season. Water deeply at least once per week if rainfall is lacking. A mature tomato plant may require 2-3 gallons of water per week. (4) Avoid high nitrogen fertilizers like ammonium nitrate.”

And if your tomatoes show symptoms? “Remove fruits immediately. Spraying affected plants with a calcium chloride solution may offer some temporary relief. Regular, deep watering will alleviate the problem if calcium levels in the soil are adequate,” the Extension advises.

Karnik’s problem tomato was a Roma. Mine are Super Marzano. Both are paste-type varieties, which the Extension’s posting indicates are especially receptive. If you remember my earlier posting about setting out the transplants, you’ll remember that I put a little pulverized limestone in each planting hole to try to prevent blossom-end rot, as recommended by the Extension.

Sometimes: Grow Them, Throw Them

I’ll still harvest lots of Super Marzano tomatoes because as the weeks pass and calcium/moisture balances adjust and later settings of fruit get the calcium they need, the problem, I think, will disappear from the Tomato Patch.

Do all paste-type tomatoes develop blossom-end rot? I have one Big Mama, another paste-type tomato, set between two Super Marzano plants, and the Big Mama—planted the same day and with the same small amounts of both lime and fertilizer—shows no sign of the problem. Several years ago I tried a European heirloom variety, Nyagous, with “black” plum-type fruit, and it had nearly 100% loss to blossom-end rot early in the season.

If your tomatoes show signs of blossom-end rot, pick and discard all affected fruit. Chances are good that fruit settings later in the season will not be affected. Next year try adding a little lime when you set out your plants. Avoid varieties that seem especially susceptible. And you might try a calcium spray, as the Extension suggested, which may be available at a good local nursery near you or by catalog or on the Internet, though I don’t know of a tomato grower who has tried it.

If you’re a gardener in a mid-Atlantic state or in a state with climate similar to that of Maryland’s and haven’t browsed the great resource postings at the University of Maryland Extension’s Home and Garden Information Center, you need to take a detour to check out this valuable online site. Let me show you the way: CLICK HERE.