Diagnosing Tomato Problems: Blossom Drop

With the heavy rains we’ve had this year, many gardeners are suffering from tomato problems. Blights and other diseases, cracking, blossom end rot, tomato hornworms — you name it, we’ve had it. This year, I’ve had a different sort of problem on what is my best-looking tomato overall. The tomato is a WonderStar Red tomato, a newish variety that I am growing as a trial for Burpee. The plant looks great, blossoms like crazy and then . . . the blossoms wilt up and die. What is happening here?

The Tomato Doctor is In

Because this is a trial plant, I was able to contact the folks at Burpee to see what might be going on and get some advice on what to do next. Josh Kirshenbaum, one of Burpee’s vegetable guys, asked a bunch of questions about how I was growing the tomato and our Minnesota weather. (It was a great lesson in diagnosing plant problems!)

Q. Has the weather been hot?

A. Not really. Up until last week, the temperatures have been below normal. Most of the time tomatoes drop their blossoms due to excessive heat. The ideal temperatures for tomatoes to blossom and set fruit is 60 to 75 at night and 75 to 90 during the day. We’ve been in that range, though our wet weather may have diminished the amount of sun the plants are getting.

Q. How big is your pot?

A. I’m growing the tomato in a 16-inch pot on my very sunny deck. I’ve grown “patio” tomatoes in that size of container many times before and gotten a good harvest. WonderStar Red is a determinate tomato but not exactly a patio tomato. Determinate tomatoes reach a set size, then make fruit, unlike indeterminate tomatoes which keep on growing and setting fruit until frost. A patio tomato is bred to stay small so it can be grown in a pot. Josh says he has grown Wonderstar both in pots and in the ground and the ones in the ground produce better, probably because they have easier access to the nutrients that are naturally in the soil. That brought us to the next question.

Q. What’s been your fertilization strategy?

A. I always put a good handful of an organic slow-release fertilizer in my pots when they are planted. But with all the rain we’ve had, that has long since washed away or gone into the plant. I’ve also given it some fish emulsion a couple of times. Recently, I decided that wasn’t enough and have given it one dose of a liquid “tomato” fertilizer. This fertilizer has higher levels of nitrogen, phosphorous and potassium than fish emulsion, with an especially high does of potassium, which helps with fruit set. Josh suggested that I also top-dress some more of the organic slow-release fertilizer to offer a slower, steadier dose of food to the plant.

So, what’s my problem?

Rain may be what’s causing the issue. After we talked, Josh checked a bit more on blossom drop and found out that being water logged can also lead to blossom drop. Because my plant is in a smallish container and it’s been damp pretty much all season, the plant is stressed enough that it does not want to produce as much fruit as it might otherwise. There isn’t a lot I can do about it at this point, but I did get a few suggestions.

What are my next steps?

I’ve top-dressed the pot with a slow release, organic fertilizer to make sure the plant has all the nutrients it needs. Another suggestion was to harvest the tomatoes I have on the plant fairly early—as soon as there is a blush of red. This sends a message to the plant that it’s time to send up more blossoms and set more fruit. Hopefully, the rain will slow up a bit (she says as another half inch has filled the guage since this morning) and the plant will have a chance to blossom more and set more fruit. For next year, I will certainly grow this tomato again but in the ground rather than in a pot.

Another tip: be patient. In Minnesota, the tomato season doesn’t really get going until August, especially in such a wet year as this. Whatever tomato problems you may have, there is still time for more fruits to be set. I’m hoping to harvest many tomatoes.