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Saturday, June 20, 2015

Tomato Plants With No Fruit. What's Happening?

Q. We have several tomato plants that had grown well with lots of leaves but there is no fruit production. We have a good soil blend and other greens like kale, red and green chard are doing well. I know that it has to do with pollination or lack of it and wonder what else we can do to help these tomato plants.
Tomato flowers not setting
A. Several factors come into play regarding tomatoes not setting fruit. Let's keep in mind that some varieties of tomatoes are better suited for our hot, dry desert climate than others. Good performing varieties have included Early Girl, Patio, Jet Star, Champion, Roma, Big Boy, Better Boy, Sweet 100, cherry tomatoes in general, grape tomatoes to name just a few. There are others as well. Heirlooms typically struggle in their production so selecting a variety that you know should perform well and then experimenting with others that are unknown is probably a pretty good idea.
Tomato flower on left has set but tomato flower on right did not.

The second problem is regarding how rich the soil is and the fertilizers applied. Extremely rich soils with a high percentage of manures can promote a lot of top growth at the expense of flower production. In other words, amending the soil with a lot of rich ingredients high in nitrogen will promote a lot of leafy top growth early in the season, delaying flowering. 

Be careful when amending garden soils that you don't overdo it with amendments. If you have a productive garden already, I would not add more than 1 inch of compost to the soil and digging it in to a depth of 8 to 10 inches. Soils that are not productive or have never been underproduction might require 2 to 3 inches of compost initially added to it with a 1 inch layer applied in subsequent years.

Starter fertilizers added to the soil at the time of seeding or putting in transplants should be fertilizers high in phosphorus (the second number) with moderate to low amounts of nitrogen (the first number). Once a starter fertilizer has been used, you should not fertilize tomatoes with a high nitrogen fertilizer until you begin to see flowers setting. After flowers have set fruit, then go ahead and feed the plants with small amounts of fertilizer once a month.

The third problem is regarding the air temperature. Once air temperatures climb above 95°F and nighttime temperatures are warm, tomatoes will no longer set fruit. 95°F is not an on and off switch for setting tomato fruit. Some tomato varieties will stop setting fruit in the low 90s and others will stop when temperatures get our bit higher.

Keep your tomatoes healthy during the heat of the summer and if summer temperatures cool off to the low 90s for a brief time they should set if nighttime temperatures are dropping as well. When temperatures climb back up again, they will stop setting again. If you can maintain tomatoes into the early fall, they will start setting fruit again when temperatures drop down.

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