Climate change seems to have brought a considerable change to our weather patterns. What are usually the dog days of summer in mid-August came in July and August brought cooler, almost fall-like temperatures. Fortunately with the cooler weather also came some rain. We are not out of a drought yet, but at least we have had to water our gardens less. This is not to say that we will continue to have cooler days ahead – we could be in for another stretch of 90° temperatures into September or beyond.
By now we should be well into harvest season, but the hot weather in July may also have played havoc with our vegetable production. There are a variety of problems that can develop because of the hot, intense sun during the day and the fact that temperatures barely cooled at night. It is possible to have plants that are lush and green but that are not producing flowers or fruit or if they do it is in much smaller quantities. Sometimes fruits or vegetables will produce a small fruit but it will fail to thrive and “die on the vine.” This year some gardeners are finding the fruit that does mature and ripen has bleached spots, which turn to brown and then begin to decay.
A possible reason for lush plants with no fruit could be over fertilization. Too much nitrogen encourages the growth of leaves, but it is phosphorus that helps the development of flowers and thus fruit. Fertilizing with a fertilizer that is heavy in nitrogen could result in the plant directing all of its energy into producing leaves.
Tomatoes are especially sensitive to temperatures. Tomatoes produce many flowers throughout the growing season, but the flowers have only a 50-hour window for pollination. The ideal temperatures for pollination are daytime temperatures below 85°and nighttime temperatures below 70°. When we see daytime/nighttime temperatures above this the plant becomes stressed and many of the flowers drop without being pollinated. Green beans can suffer the same fate in temperatures over 95°, especially if the soil is dry. Sometimes even pollinated flowers will abort when temperatures are consistently too high. Another pollination problem is that bees don’t like the heat! In temperatures over 90° bees are less active. Less bee activity, less pollination.
Vining members of the cucurbit family, such as squash, cucumbers, melons and pumpkins suffer a unique problem from the heat. Cucurbits produce separate male and female flowers on each plant. (Female flowers have a swollen stem below the flower where the ovary is located; male flowers have straight stem.) Higher temperatures favor the production of male flowers. With few or no female flowers to pollinate, little or no fruit can be produced. If you have zucchini plants that produce a lot of flowers but no zucchini this could be the problem.
You may have avoided all of the above problems and have plants with plenty of fruit but it seems like it is taking forever to ripen. Patience and cooler night time temperatures may be needed. Tomatoes can take 6 to 8 weeks to ripen and some vine crops almost as long. Tomatoes ripen in two stages. In the first stage they mature, get green and seeds are formed amidst a jelly like substance. If you have ever eaten a fried green tomato you are eating a mature green tomato. In the second stage the tomato continues to mature and turn red. This maturation occurs in temperatures between 68° and 77°. The pigment that produces the red color is not produced in temperature over 85°. So contrary to what we might think, cooler nighttime temperatures will move the ripening process along.
Exposure to intense summer sunlight can also produce another problem in tomatoes, peppers, cucumbers, squash, raspberries, pumpkins and even apples. When it happens to us we call it sunburn–in fruits and vegetables we call it sunscald. You might first notice bleached white spots on your fruits. The intense sunlight has caused cells to break down and die. The white spots quickly turn brown, and decay sets in as other microorganisms move in. Apples are a little more resistant to sunscald so they generally only develop brown spots. Leaves provide the natural shade for fruits, so having lots of leaves can help with this problem. (Avoid watering your leaves so as to avoid foliar diseases that will cause the leaves to drop.) Move potted plants into a shadier location; otherwise try using a shade screen. If you do have some fruit damaged by sunscald remove it so the plant will put more of its energy into the removing fruits.
I hope you have a bountiful harvest in spite of the crazy weather we have been having. We may have to adjust some of our gardening practices as I am afraid this will be more of the norm in the future.