As a result of all the questions I have been getting this year about tomato plants not developing flowers, I have come to realize a few things.
First, a lot more of us are growing tomatoes. Whether this is because of an increase in outdoor greenhouses, the invention of the "Topsy-Turvy" grow bag, too many columns on the subject or the realization nothing tastes better than a fresh, organic, home-grown tomato, I do not know. All I know is this year I have had an incredible increase in tomato questions, which can only mean more readers are growing them.
Second, many people don't know much about growing tomatoes. It is no wonder. In the Lower 48, tomatoes are so easy to grow you find them self-seeding from year to year in some gardens -- literally so easy you don't even need to plant them. And it doesn't usually matter what kind of plant is used, because the growing season is long enough to accommodate them all.
Not so here in Alaska, and to answer the most asked question about too few tomato flowers, you first need to know that there are two basic kinds of tomato plants.
The "determinate" plants grow to a set height and usually produce all their tomatoes within a short period of time and then die. They are usually early season producers with only one main stem. The "indeterminate" plants grow like vines, continually, produce suckers and can branch out. They produce fruit continuously or in several spurts, usually about three weeks or so apart until they are killed by the frost. These often include late producing plants.
So, the first thing to figure out is what kind of plants you have and when they are supposed to bloom. I warn folks all spring to label their plants. Here is a great reason to do so. If you don't have the package laying around, you can Google the variety and find out how long after it is planted it is expected to produce fruit.
Somewhat related are knowing the varieties of tomatoes you try to grow. I grow special, heirloom plants with weird looking tomatoes that sometimes need conditions I can't give them in our short season, but I expect this. If you don't, then stick to the kinds known to be suited for our light, temperatures, use of greenhouses and short season.
Next, growing tomatoes in a greenhouse presents special challenges. Alaska greenhouses can get way too hot and, because of our longer days, can remain too hot longer than Outside structures. Once temperatures get around 95 degrees, tomatoes shut down. They are stressed, and stressed tomatoes don't produce flowers. Ventilation is the answer, as is a recording thermometer to measure high and low temperatures for the day. You can get one at any hardware store.
Similarly, many Alaska greenhouses get too cold when our subarctic evenings kick in. And, there can be several days in a week when the temperatures don't reach the requisite level. Unfortunately, most summer greenhouses lack heaters. In short, you may need to have some sort of additional heat source set on a thermostat. Know, too, that temperatures above 60 (and ideally 65 to 70) during the night will provide plants with the least stressful environment, and they will produce more flowers.
While it is important your tomato soil remains moist at all times, keeping it too wet will also stress the plants. Don't overwater. If you don't have adequate drainage, you are overwatering. Speaking of soil, if you are not giving your plants enough room to grow, they won't flower well. Five gallons is the usual suggested minimum. It is not too late to transplant tomatoes if yours are in small containers.
Next, nitrogen is way too often overapplied to tomato plants in Alaska. It's a knee-jerk reaction to putting them out in the greenhouse. This result is lots of healthy leaves and big plants but also few or no flowers. In fact, gardeners are programmed to toss all sorts of things on tomato plants, from Epsom salts and Miracle-Gro to fish emulsion and manure The truth the commercial guys don't want you to know is if you use good composted soil and mulch your plants with brown leaves, tomato plants probably won't need any other feeding. They grew very well in the years before Miracle-Gro.
Having said this, tomatoes can be finicky, but don't do anything until they show some signs of needing help. In short, leave them alone and they may just do better in terms of producing flowers..
Finally, if you must put something on tomatoes and need something quick when they show signs of needing help, try kelp meal mixed into the soil before you plant. This is loaded with micro-nutrients. If you must fertilize, use something with a higher middle number -- phosphorous -- than the other two in the fertilizer trilogy on the label.
Jeff Lowenfels is a member of the Garden Writers Hall of Fame. You can reach him at teamingwithmicrobes.com or by calling 274-5297 during "The Garden Party" radio show from 10 a.m. to noon Saturdays on KBYR AM-700.