Thursday, August 5, 2010

Hot Weather Garden Problems by Carol King and Donna Duffy

The Dog Days of summer are here. The Greeks and Romans believed the dog star Sirius, a prominent star in the August heavens,  was the cause of the hot, sultry weather. They considered this to be an evil time "when the seas boiled, wine turned sour, dogs grew mad, and all creatures became languid, causing to man burning fevers, hysterics, and phrensies" according to Brady’s Clavis Calendarium, 1813.
It’s also the time in the garden when hot weather causes all sorts of calamities as well and gives gardeners fevers, hysterics and phrensies!  Be on the lookout for these problems.

The lawn is getting brown! The lush green grass from spring is starting to dry up with the hot days. If your lawn is Kentucky bluegrass (very common in landscaping) this slowdown is a natural part of the life cycle. Tip #1: mow to a height of 2.5 to 3”, and return the mulched clippings back to the lawn. Tip #2: fertilization is typically not necessary from July to early August. Wait to fertilize until late fall while the grass is still green. Tip #3: when a lawn looks thirsty, a common mistake is to increase the watering time. When using a standard sprinkler system with pop-up heads, eight to ten minutes is about the optimal time any one turf zone should run so run-off doesn’t occur. The full cycle may need to be repeated two or more times depending upon rain, humidity, wind and heat in the environment.

Yikes! Spider mites! Spider mites are common pest problems on many plants around yards and gardens in Colorado. Damaged areas typically appear marked with many small, light flecks, giving the plant a somewhat speckled appearance. You might also see webbing. Tip: few insecticides are effective for spider mites and many even aggravate problems. Instead, try a periodic hosing of plants with a forceful jet of water to physically remove and kill mites, as well as remove the dust that collects on foliage and interferes with mite predators.

Leaf scorch. During the hot days of summer, many trees, shrubs, flowers and vegetables develop dry, brown leaf margins. Once leaf scorch has occurred, there is no cure. The dehydrated portions of the leaf will not turn green again, but with proper water management, the plant may recover. Tip #1: during the growing season, water deeply and infrequently. Resist the urge to water more frequently. Tip #2: in the winter, give the plant a deep watering once a month when there is no snow cover. Tip 3: avoid overfertilizing. Fertilizer spikes, that deliver concentrated salts at specific sites, can burn roots and contribute to leaf scorch.

Pollination issues.  Many summer vegetables must be pollinated by insects such as bees to set fruit, During hot weather, pollen doesn’t remain viable very long. As a result there may be a drop in vegetable production for several days during and after hot spells even if bees are present. There may be more misshapen fruit as a result of poor pollination.

Blossom drop. Temperatures in the nineties cause many vegetables to drop their blossoms before fruit forms. Squash, zucchini, tomatoes, and beans are especially prone to this. Over fertilizing and under watering also contribute to blossom drop. Tip #1: To minimize blossom drop during a heat wave, keep your garden well watered by applying around 1” of water per week if it does not rain. Tip #2: avoid high nitrogen fertilizers.  Tip #3: Mulch the vegetables to conserve moisture and keep soils cool.

Blossom end rot. Another problem that is common in hot weather is blossom end rot (BER). This disorder occurs when there is not enough calcium available to developing fruit, resulting in the lower end of the fruit turning tan or black and failing to develop. BER is most common in tomatoes, but also occurs in eggplant, peppers, watermelons, and squash. The most common causes are uneven watering, over fertilization, extreme temperatures, and low soil pH (acid soil). Tip #1:  keep vegetables evenly moist. Do not allow them to dry out during dry spells. Tip #2: do not over fertilize with high nitrogen fertilizers.

If you have other “phrensies” in the garden, call the Jeffco CSU Extension Office at 303-271-6620.  We’ll get through this together!