By Ellen Barcel

Late autumn is a great time to access your gardening successes and failures. It’s well into November as I work on this column. My tomato plants have been very weird this year. I’ve grown tomatoes for decades. I’ve never had trouble with tomatoes setting fruit, always having a bountiful crop (except when the tomato blight struck). That is, until this year when I had few blossoms and no fruit.

This was a new experience for me. So, that got me started researching why the fruit would not set. All the information I’ve been able to find gave me some hints, but, none really explained why, now, well into autumn, the plants are setting fruit. Yes, I’ve got at least a half dozen green tomatoes and many more blossoms. And I’ve noticed two other gardeners whose plants were covered in green tomatoes in late October.

So, first some basic information on tomato plants in general. The tomato, which is a member of the nightshade family, was developed in Mesoamerica. Having been developed in such a mild climate, it needs warm weather to grow successfully. While many other plants can be put out in early to midspring, experts recommend not putting your tomato plants out until Mother’s Day (mid-May), although my father always said Memorial Day (the end of May), because they are so tender.

Tomato plants do not need a second plant to provide pollen like, let’s say, a holly bush does. There you need at least one male plant in the area usually for up to four or five female plants. Nor do they have different male and female flowers on the same plant, the way squash does. Look carefully at squash and you’ll notice that the early flowers do not set fruit since they’re the male ones. Then the female flowers open and soon they are the ones to produce fruit.

The tomato flowers contain both the male and female organs in the one flower. Usually a gentle breeze or insects causes the pollen to fall so the flower can pollinate itself. People who grow tomato plants in the house or in a greenhouse must help their plants along, gently shaking the plant or providing a gentle breeze to release the pollen.

Now back to the tomatoes outside. So, why no fruit?

◆ First of all, always keep your plants healthy by providing adequate fertilizer and water. Tomatoes are heavy feeders, and healthy plants are more likely to bear fruit.

◆ When the day temperature goes above 85 to 90 degrees, the pollen is no longer viable. Optimal day temperatures for setting fruit is 70 to 85 degrees.

◆ To set fruit, night temperature should be above 55 but below 75 degrees. If Mother Nature doesn’t cooperate with the adequate temperature range, the plants will not set fruit.

◆ In very humid regions, the pollen may become very sticky. It therefore won’t fall through the flower.

◆ Tomato plants need six to eight hours of full sun. Plant in an area with too much shade and you don’t get fruit.

◆ Tomatoes also need lots of water. If you’ve ever experienced blossom end rot, cracks in the bottom of the fruit, it’s due to the soil drying out. So, while you don’t want to plant the tomatoes in a marshy area, you do want to make sure that they have a consistently moist soil.

◆ Fungal diseases, such as the tomato blight of recent years, can also be a problem.

◆ Determinate plants set fruit early, while indeterminates need to be a bigger plant, so set fruit later in the season. Determinate plants are more compact. They are varieties that reach a certain size and no bigger, such as ‘Bush Early Girl,’ ‘Better Bush,’ ‘Elfin’ and ‘Grand Cherry.’ Indeterminate plants like ‘Big Beef’ and ‘New Girl’ keep growing like a vine. If conditions aren’t right later in the season, you won’t get fruit from indeterminates.

◆ Fertilizer with too high a nitrogen content leads to lush (lots of greenery) plants but not necessarily lots of fruit. Use a more balanced fertilizer, such as one whose label reads 10-10-10.

So, why didn’t my plants set fruit this summer? My guess is that they weren’t getting enough sun and I moved them to a more sheltered area, one without a breeze or insects to release the pollen. Next growing season the plants go back to where I grew them in past years. As to why they’re setting fruit now, my best guess is that we’ve had a very mild autumn, and therefore Mother Nature has provided the right day and night temperatures for fruit to set.

A final note — if you are growing plants from seed, you need to start them six to eight weeks before you plan to put them out. Start late March or early April and in a sunny window. If the plants become very leggy, the stem can be planted deep into the soil outside as roots will develop anywhere along the stem. Putting them outside in a cold frame first helps to harden off the tender plants, but watch the weather. If a cold spell is predicted in early to mid-May, hold off bringing them outside until the weather is warmer. To maximize tomato yield, select early, midseason and late tomato plants.

Ellen Barcel is a freelance writer and master gardener. Send your gardening questions and/or comments to [email protected]. To reach Cornell Cooperative Extension and its Master Gardener program, call 631-727-7850.