By: Sandy Feather ©2011
Penn State Extension
Q. I think this the worst summer I’ve had as a vegetable gardener in over 20 years. I haven’t gotten many tomatoes, although I am finally starting get more. My peppers and squash have been equally unproductive. I do not understand – I’ve had my soil tested and followed all the recommendations, took steps to control insects and really did not seem to have disease problems like the late blight epidemic that devastated my tomatoes in 2009. I use soaker hoses to keep the garden watered during hot, dry weather. But my yield is way down – what gives?
A. This has been a challenging growing season, starting with torrential rains in the spring, followed by unusually hot and dry weather. The heat wave has impacted flower and fruit set on many crops. Although peppers, squash and tomatoes are warm season crops, they are most productive in a fairly narrow temperature range. When temperatures get too high (or too low), production suffers, and plants can even die if temperatures are too extreme.
According to Elsa Sanchez, Associate Professor of Horticultural Systems Management at Penn State, University high temperatures have been shown to reduce flower development and cause abnormal growth and development of male and female flower tissues. That can mean no fruit or small, misshapen fruit.
For example, tomatoes are most productive when daytime temperatures are in the 70 to 85 degree range and nighttime temperatures are between 59 and 68 degrees. Daytime temperatures above 90 degrees causes reduced flowering and fruit set, as do nighttime temperatures above 70 degrees. Research indicates that high nighttime temperatures may be more disruptive to pollen development than daytime heat.
Tomatoes are most productive when daytime temperatures are in the 70 to 85 degree range and nighttime temperatures are between 59 and 68 degrees
High humidity can also hamper pollination in tomatoes because the pollen remains stuck to the anther (the male, pollen-producing part of a flower) or clumps together in such a way that inhibits complete pollination. Peppers and tomatoes are in the same family, and peppers react pretty much the same way to high temperatures.
Sanchez also noted that cucurbits such as squash, cucumbers and pumpkins – species that have separate male and female flowers on the same plant - tend to produce all male flowers when temperatures are 90 degrees or above. Male flowers provide pollen, but not fruit, so it is not surprising that your squash yield is down as well.
While you cannot change the weather, there are some steps you can take to help your vegetable garden through the heat. Provide an inch or two of water a week, preferably in one or two long soaking sessions. The idea is to wet the soil four to six inches deep to encourage the plants to develop a deeper, more drought resistant root system. Watering a little every day has the opposite effect: it encourages plants to have shallow root systems that have little drought tolerance.
It is also important not to overwater during hot, dry weather. Stick a finger two or three inches into the soil to feel the moisture level. If it still feels damp, hold off watering another day; if it is dry, go ahead and water. This rule of thumb applies to ornamentals as well as vegetables.
Mulching the vegetable garden with three or four inches of clean oat straw helps conserve soil moisture, moderate soil temperatures and helps keep weeds down that would otherwise compete with the vegetables for water and nutrients.
Now that the weather has moderated, these crops should begin producing again. If only the fruits get a chance to mature before the first frost!