By Sarah Robertson
commentary | Posted: Sunday, July 27, 2008 12:00 am
The cause-and-effect of hot weather and insufficient moisture is immediate and occasionally deadly for plants grown in pots or hanging baskets, forcing gardeners to be ever-vigilant.
We're a bit slower to spot the ramifications of major summer heat on seemingly imperturbable vegetable crops such as potatoes, beans, cucumbers and corn.
Sufficient water, needless to say, is critical at this point in the season if you desire prolific and delicious mid-to-late-season crops. Often times the amount of water given a plot is perfectly adequate, but rampant leaf growth makes it impossible for water to penetrate down to the soil. The end result? Lackluster plants and bitter, sometimes inedible, vegetables.
This is especially true if crops were spaced just a bit too tightly back in April, May and June. Factor in our national love affair with overhead sprinkler irrigation and bingo - water stress 101.
In my daughter's vegetable bed, for example, slender starts invariably morph into large, sprawling plants with leafy canopies. Water from the sprinkler rarely penetrates the foliage, leaving the soil underneath fairly dry. The result? Limp and wilting plants on those days we neglect to give those veggies additional water by hand.
But it doesn't have to be this way! Here are a few tips that should help the most susceptible members of your vegetable crop sail through the hot days ahead. With many thanks to Dorothy Hinshaw Paten and Diane E. Bilderback, authors of the terrific vegetable-growing book, "The Book of Garden Secrets" (1997, Firefly Books Ltd., $19.95 paper):
n Potatoes: This delightful vegetable is a veritable starch-and-water machine, consuming moisture at a fast clip in order to facilitate tuber expansion. Irregular watering results in knobby, misshapen potatoes and can also cause hollow heart, which is a cavity in the middle of the tuber. Regular, deep watering is vital from the time flowering begins (and tubers start to form) until just before the foliage dies. In other words, the soil should be kept consistently moist to the touch.
How to accomplish such a task when faced with the typical Western Oregon summer of little to no rainfall without racking up a horrific water bill?
Mulch. Yep, a nice thick layer of straw, dried grass clippings or shredded bark is the key to plump, tasty tubers and tolerable water bills. Mulching also eases the stress felt by potatoes during periods of intense heat. High temperatures causes potato foliage to wilt. Even well-watered potato plants wilt when temperatures rise above 90 degrees, which slows down photosynthesis and can have dire consequences on the size of your harvest.
Since much of Oregon experiences regular stints of really hot weather during the summer months, it makes sense to keep susceptible plants as comfortable as possible. Mulching, deep watering and careful pruning to reduce unnecessary runoff are your best bets.
n Beans: High temperatures can cause blossom drop, which is bad news for gardeners hoping for a bumper bean crop. Scorching weather can also cause the development of seedless pods in dry bean cultivars.
If the thermometer rises just when your beans are flowering, you can often save your crop by spraying plants with cold water during the afternoon. Friends with a much larger garden than mine drape shade cloth over their bean patch whenever temperatures go above 80 degrees F. The cloth sits high enough above the poles to encourage air circulation while simultaneously cutting down on those really blazingly hot rays.
n Cucumbers: Research has shown that cucumbers are actually quite sensitive to cold water. In fact, if you water cucumbers with really cold water, they may actually wilt! The tips of developing fruits may dry out and the leaves and fruits can become discolored and even die.
Since cold water is pretty much universally unavoidable, your best bet is to water all curcurbits later in the morning, when the soil is being warmed by the sun. Cucumbers, muskmelons and watermelons are more susceptible to cold water than summer or winter squash.
n Corn: This crop requires 12 to 24 inches of water during the season to produce well, so be generous with your watering! You can tell that corn plants are moisture-stressed when their leaves roll up lengthwise. But don't let 'em reach that point. If necessary, turn on the hose and let it gently flood the corn patch until the soil is uniformly moist down to a depth of at least six inches. Allow the soil to dry out slightly before repeating the process.
If water stress occurs while your plants are shedding pollen, say Bilderback and Patent, the pollen may not be viable. In other words, it may not pollinate the female flowers. Greenhouse studies have shown that ears from plants that were water-stressed for one week after the silks appeared had 50 percent fewer kernels than ears from plants given sufficient water.
The importance of water showed up again in the study five days later, as the kernels were filling. Water stress during this period halved the kernel weight, compared to normal ears.
Remember, corn is a grass and its lower leaves are the first to show signs of nutrient deficiencies. Watering with compost or manure tea is a great way for corn plants to receive an immediate boost.