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 “rot” on Super Marzano tomatoes

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.”

Fruit of all sizes 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.

Sometimes: Grow Them, Throw Them Away

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.

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.

7 Comments on “Tomato Patch: An ugly problem

  1. I'm having a big problem with blossom end rot on my “Speckled Roman” plum tomatoes. They have a very long shape (I think they are a cross between Roma and Banana Legs) and the rot starts at the bottom and by the time the fruit is ripe the rot has moved all the way up. I use lime, and also ground up eggshells to add calcium, but I'm still having a problem with this particular variety. Last week I added another dose of eggshells and dissolved some epsom salts in my watering can and watered deeply. I'm hoping the break in the heat will help get me some of these amazing tomatoes; they're red w/orange stripes and the taste is superb! -Anne


  2. All of my San Marzano Redortas have rotted so far. I'm treating them exactly the same as my San Marzanos and my Chocolate Stripes, but have had only 1 of each of those rot. I just started epsom salts this week, and I guess I'll try some calcium.


  3. I guess I got lucky. I failed to put down lime this year for my tomatoes and haven't noticed any blossom end rot. I planted Roma, Big Boy, Sunbrite, and Grape. I did read on the GIEI website that I should mix in lime during transplanting, but I didn't for some reason. I will have to thank the person who had my plot before me if I can figure out who it was.


  4. Every fruit on two Roma plants have had end rot. Some of the tomatoes I picked just as the rot was starting to show — I let them ripen on my window sill and all was well. The rest I just chopped the rotten end off and made a great big batch of salsa… it was delicious! (I just couldn't stand the thought of tossing an entire crop.)

    Next year I will definitely had limestone and install a watering system on a timer…


  5. Mike McGrath recently said about it when symptoms are visible;

    ..” dissolve some TUMS or another form of calcium carbonate in water and give that to the plants. I'll say use half a dozen 1,000 mg tablets in a regular size watering can. The next runs of fruit should be fine. Repeat this in about three weeks.

    And next year, save up your eggshells from around New Year's on and put the crushed shells of a dozen eggs in each planting hole — that totally prevents the dreaded rot! “


  6. Wow, thank you, all you blossom-end fighters! Some comments/opinions:

    1. My dad taught me to use epsom salts in the garden for “good healthy plants.” But epsom salts is manganese sulfate, which will not supply missing calcium to prevent rot.

    2. Egg shells will add calcium to your soil as they deteriorate over time. I know a gardener who puts her shells in a blender with water to pulverize them and speed their deterioration once she add them to the garden. Dissolved Tums, though pricey, should help future settings of fruit, but obviously not the one already with black ends.

    3. In short, it's still calcium ions, plus moisure/water, plus varieties that aren't extra sensitive to the problem. For me, I've given my Super Marzanos pulverized lime and water when I planted them, I've watered them regularly, and they have a significate rot problem. I'll try another variety of paste tomato next year. Send me your recommendations!


  7. So far, my San Marzanos are better than last year with the blossom end rot (some are still affected). Polish Linguisas look pretty good right now and the Howard Germans look to be just fine, too(first year trying these and they are goegeous!). But the Green Zebras are 100% affected. All we did this year was put a scoop of dolomitic earth in each hole.


Leave a Reply to Cheryl McDaniel Keffer Cancel reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: