As temperatures rise, we start to see a common problem in the vegetable garden. You may notice that your plants are producing lots of flowers, but little to no fruit is being set, and that means little or noth­ing to harvest. While this problem is most noticeable on tomatoes, it also affects peppers, beans, squash and several other summer crops.

What causes summer vegetables to appear healthy but fail to produce? Shade or too much nitrogen could do this, but in mid-summer the heat is often to blame. Research has shown that as daytime temperatures rise over 90 to 95°F and nighttime temperatures above 70 to 75°F, fruit set in many vegetables declines and in some cases stops. This is partially due to poor pollen or sterile pollen production during high night temperatures and explains why this phenomena happens more often in our coastal areas where the nights stay warm. Without viable pollen, plants cannot set fruit and the flowers abort or drop off. Individual varieties respond to heat differently so you may notice that one variety of tomatoes continues to set some fruit while another one shuts down entirely. Fruits that do set often ripen very slowly.

This slow ripening is related to the second reason that plants may stop setting fruit during the hottest part of summer and that is water stress during the heat of the day. Plants need water to fill the cells of the fruit being produced. When daytime temperatures reach up into the 90s, many plants have trouble moving enough water into their leaves to keep them from drooping, even when there is enough water in the soil. When plants can’t keep their leaves full of water, they also don’t have the water to spare for producing fruits such as tomatoes, peppers or beans. In addition, plants under water stress close the stomates or tiny pores in their leaves that allow gas exchange. Closing the stomates protects the plant from unrestricted water loss. But these stomates are also where carbon dioxide is exchanged with the atmosphere. This carbon dioxide is necessary for photosynthesis – the plant process that results in the development of sugars and energy for plant growth. So plants under water and heat stress have to make a choice – they close their stomates to survive but that means that they are just maintaining rather than growing vigorously and ripening fruit.

While still edible, the fruits that do mature during hot weather are usually less flavorful than those that ripen under more mild conditions. Green tomatoes that have already formed on the vines will continue to ripen, but often do so unevenly. A common heat related complaint is yellow or green shoulders – this occurs when the top of the tomato fruit stays green or yellow while the rest turns red. Yellow shoulders occur when the surface temperature of the tomato heats up and inhibits the development of red pigment. Maintaining a nice cover of leaves on the plant by controlling foliar diseases and not overpruning is a good way to prevent yellow shoulders.

A less obvious disorder is the development of internal white spots on the tomato. On the outside, the fruits usually look completely normal but when cut open, you will find areas of hard white tissue within the fruit walls. Some varieties are more prone to developing internal white spots than others. This condition is exacerbated by low soil potassium. So go ahead and test your soil, to determine just how much potassium and other nutrients your garden needs.

Fortunately, one day of these extreme temperatures is not enough to cause problems. Instead, it’s the accumulation of five to seven days or more in a row that causes problems when it comes to production. There is little gardeners can do to control the weather. However, there are a couple of steps that we can take to ensure our garden is as productive as possible. First, water consistently to keep soil evening moist. Do not allow plants to dry out during dry spells and do not over fertilize with high nitrogen fertilizers. Make sure you harvest frequently to keep vegetable plants productive. Leaving fruit on too long reduces the amount of fruit that the plant will set in the future. So be sure to pull large fruit off the vegetable plant before they drain energy necessary for new flower production.

Follow these steps to keep your garden healthy during the heat of summer so when the temperatures cool down a little, production will start back up.