Tomato Harvest Down? Blame the Heat

A recent string of comments on the University of Minnesota Extension Master Gardener listserv answered a question I’ve been wondering about: Why  do my tomato plants look so stellar and yet have very few fruits? The short answer is blame the heat.

Blossom drop is a fairly common problem with tomatoes (though not the problem I usually have). What happens is that your plants look great, with lots of green foliage, put out plenty of blossoms, and then the blossoms just wither up and drop off the plant. I noticed this happening almost a month ago, and my first concern was that bee numbers might be down (unfounded, it turns out) and perhaps the fruits were not getting pollinated.

But the Master Gardeners pointed out that the combination of high temperatures and high humidity—exactly the weather pattern we have been stuck in for several weeks—is a frequent cause of blossom drop. Tomatoes like daytime temperatures between 70 and 85 degrees F and they don’t like the humidity to be above 70 percent. We’ve been in the 90s frequently and above 70 percent humidity regularly.

Moreover, the amount of rain we’ve had and its tendency to come in deluges could be washing away some of the nitrogen the plants need, also contributing to blossom drop. I’m growing a few tomatoes in pots and a few in the ground, and the ones in pots got a good shot of worm-poop fertilizer a couple of weeks ago, so I do not think that is my main problem.

I’m hoping the weather may correct itself soon and the plants will get a chance to set more fruit. In the meantime, I’m coddling the few tomatoes that are ripening on the vine.

Slime Mold Attacks! Blame Heat Wave!

Slime mold in action

Sorry for the National Enquirer imitation, but I was pretty taken aback Wednesday evening when I discovered these tan blobs on the mulch in one of my gardens. It looked like the world’s largest bird poop, sort of. Other sources compare it to dog vomit.

I took a photo and after a quick Internet search discovered that I have “slime mold.” This basically harmless fungi preys on mulches in times of high heat and humidity. That makes sense since we’ve been setting humidity records nearly every day this week and the temps have been consistently in the 90s during the day. The mold “engulfs its food,” according to this helpful article from Texas A&M University. There isn’t much to do about slime mold except control watering and hope for drier days ahead. Fortunately, those are in the forecast for next week.


Black Spot Lookout

I only have two roses in my yard, both of which are tough and disease-resistant. But with the incessant rain we have had recently, my guess is many rose growers are on the lookout for black spot. My recent column for the St. Cloud Times covers how to diagnose black spot and other fungal diseases on roses and what to do about them.

How are your roses holding up?

Good Habits = Healthy Plants

Most people know that habits make a big difference in health. If you get plenty of sleep, drink six to eight glasses of water a day, eat lots of fruits and vegetables, and get some exercise every day, odds are you’ll be healthier. Good habits are not a guarantee against disease and injury, but they sure do help.

The same can be said of plants. Put them in the right place, give them the right care, and they will likely do well. During the Master Gardener Core Course last Saturday, extension educator Michelle Grabowski noted that less than 10 percent of home landscape problems warrant the use of a pesticide. Good cultural practices (ie, health habits) and choosing the right plants for your environment will take care of nearly all potential disease problems, she said.

What constitutes a health routine for your plants?

Buy carefully, place carefully. Read the plant tag before you buy a plant. Make sure you have the right environment in your yard for that plant to do well. If you have a shady, moist backyard, don’t expect a drought-tolerant, sun-loving plant such as sedum to do well there. While you are in the nursery, do a mini-inspection not only of your plant but the plants around it. The entire group of plants should look healthy before you plunk down your money.

Give them space. Plants need room to breathe. You’ll have fewer disease issues if you space plants far enough apart to get to full size without bumping into each other. Air circulation is a huge factor in prevention of fungal diseases.

Water. Like people, plants need enough H2O. Grabowski offered a few tips on watering, including the advice to water the soil, not the plant; water early in the day if possible; and to mulch to reduce the humidity in the air around your plants. Also, remember that water needs vary — from plant to plant, and season to season. A newly planted tree needs regular watering to establish roots; a prairie grass can tough it out just fine.

Fight germs. Keeping tools, trellises, stakes, and cages clean will help fight diseases, too. Don’t put tomato cages around new plants if they have plant debris from last season. (Oops! I think I did that last year.)

Regular checkups. As with people, it’s easier to fight a serious disease in plants if you catch it early. When you are out in your garden, take a couple of moments to check the undersides of leaves or the inner leaves on plants — that’s where diseases start.

Get the right diagnosis. You can’t figure out what to do with a plant if you don’t know what the problem is. The University of Minnesota has a fabulous plant diagnostic on its web site. If you aren’t sure what’s wrong with your plant, go to the what’s wrong with my plant site.