Is the heat taking a toll on your tomatoes this year? High temperatures and lack of moisture is problem being experienced by tomato growers in our area. Tomatoes are the most popularly grown garden plant; but as they are warm season plants, pollination and developing fruit are highly sensitive to both moisture and temperature extremes.

When daytime temperatures reach 90 degrees and above, any tomato flowers which opened earlier that morning can abort and drop off the plant. Temperatures over 90 degrees also inhibits lycopene development, the red pigmentation in the fruit, thus those tomatoes present on the vine may remain a yellow-orange color.

Cool nights may also interfere with tomato fruit set. When evening temperatures fall below 55 degrees, pollen will fail to develop in the tomato flower and any blossoms that open in the morning will not set fruit.

Other reasons for poor tomato fruit production include fluctuations in soil moisture, so keep roots uniformly moist throughout the growing season. Lack of moisture can lead to blossom end rot, a condition due to lack of calcium. But as our Iowa soils have ample calcium, additional applications of calcium are not required. Available soil calcium it is transported from the soil to the fruit by regular watering practices and will keep calcium supplied to the fruit. By avoiding extremes in soil moisture levels, the available water to the plant will provide the calcium needed on a regular basis. On a hot dry day, just one missed watering can lead to cracking and blossom end rot, the blackened area appearing on the base of tomato fruit.

Soils low in nitrogen will produce tomato plants with weak vines that cannot support a crop. However, do not over-apply fertilizer, as too much fertilizer high in nitrogen can cause blossom drop, with plants producing excessive foliage, rather than setting fruit.

Did you know? Eggplant and peppers are also warm season plants that may experience low fruit set. Use of mulch around your plants to help retain moisture, prevent weeds and disease problems to provide best possible growing conditions.

Questions? Contact McCormick at yvonne@iastate.edu for information or advice.