5 problems in the late spring garden

-- Why are the leaves curling on my tomato plants? The easiest answer is that it's not watered enough. The leaf curling is the plant's way of protecting itself, lessening the amount of water lost to transpiration.  Tomato plants thrive on deep, infrequent watering, sending out their roots deep into the soil. Frequent short irrigation times do very little to develop long roots, and the plants will become more stressed as the temperatures rise. There are other, more serious reasons leaves will curl, but if the plant looks healthy otherwise, at this time of year the answer is likely watering.

-- Speaking of tomatoes, one of the plants has some yellow leaves with brown or black spots. What's wrong? Oh, now this is not something to ignore. There are several diseases that can cause spots, including early blight, which we don't usually have to deal with in our dry summers, but the May rain we received may be the culprit here: Early blight is spread by splashing water and germinates on moist leaves. Cut off the infected leaves and dispose of them; do not compost. Avoid overhead watering.

The other possible diseases are bacterial spot or bacterial speck. These diseases also can be spread by overhead watering, splashing rain or working with wet, infected plants. Handle the diseased leaves just as with early blight.

In all of these cases, warm, dry weather will reduce the spread of the disease. Make sure the plant stays healthy: Stress invites pests (such as spider mites) and other diseases. 

-- One more tomato problem: The plant has flowers, but it's not setting fruit. What's happening? Tomatoes like warm weather, but heat spikes (over 95 degrees) will dry out the pollen, preventing fruit set. Also, tomatoes are wind pollinated. Help them out by flicking the open flowers with your fingers. (Don't waste money on blossom-set spray -- it's effective at low temperatures, not high ones.) See more advice on tomatoes and heat here

-- Why do my squash plants wilt in the afternoon? Remember those curling tomato leaves? Squash plants (and pumpkins and melons) also react to afternoon heat by reducing their leaf surface. Wilting leaves in the afternoon are not worrisome; wilting in the morning hours means the plant needs water.