SUMMER STRESS IN THE DESERT

Spring has finally ended and what a nice one it was with lots of weather changes and no early hot spells. Now summer is here and with it comes problems for gardens and landscapes.

The combination of extremely hot temperatures, low humidity and strong winds mean special precautions are needed to protect your plants. Understanding how summer stress affects plants and what you can do about it will help you garden successfully. Here are the top three causes and cures:

Improper plant location: Approximately 85 percent of all plants in our valley are non-native and aren't adapted to the desert climate and most are very sensitive to desert exposure. If you put the wrong plant in the wrong place, you'll probably see one or more of the following symptoms - burned leaves, discolored or cracked bark often with oozing sap, papery areas in leaves and repeated lanky, soft growth which slowly blackens and dies.

Causes: Putting the wrong plant in the wrong place. Some plants that are otherwise sun loving may burn when placed next to a light colored wall or reflective glass surface that faces south or west. This can also happen next to an area of paving or a rock-filled landscape. Fruit trees and many species also have a problem with trunk sunburn, usually on the southwest side of the trunk. Sunburned areas can ooze sap that can attract ants, green beetles and borers. Conversely, sun loving plants often fail to grow well when given too much shade. Expect weak, droopy, pale growth that may slowly shrivel and die.

Cures: Learn the needs and tolerances of your plants, do your research. Don't be fooled by a grower label that reads "Full Sun." That may not be the case if the plant is going in a hot spot. The "Plants for Dry Climates" book by Duffield & Jones is an excellent source; the "Sunset Western Garden Book" is another. "StarNote 530, Reliable Plants for Hot Dry Climates," available at all Star Nursery locations, will give you some good ideas.

If plants are improperly located, move or replace them. In the case of newly planted, well-adapted plants showing signs of stress use a surface mulch to lower soil temperatures. In rockscapes, replace rock around the plant base with a 2- or 3-foot circle of bark mulch. Paint exposed trunks of young fruit and willow trees with a white or off-white water-base paint.

Don't prune sunburned foliage from plant tops in summer. It provides protection for the rest of the leaves under the damaged areas. Prune in fall when weather cools. Many plants develop increased sun tolerance as they age and become established. It's worth pampering them while they are young.

Improper watering shows up in the form of wilting, scorched leaves with brown edges. New leaves emerge yellowish to off-white with green veins or the plant dies suddenly and exhibits a freeze-dried appearance.

Over watering or under watering: These are opposite problems with a very similar appearance. The reason is simple. When under watered, the plant collapses from lack of water. When too much water is applied the water drives oxygen out of the soil. It suffocates roots and prevents the plant from getting enough water and air. This causes the plant to collapse.

In desert climates, over watering is the number one cause of plant death. Most of our soils are heavy, alkaline clays with layers of caliche (calcium carbonate) and poor drainage. When watered too frequently for short amounts of time, the soils become "bathtubs" full of salty water. High alkalinity, kept in constant solution by excess water, causes nutrients to become unavailable to plants, even if supplements are applied. The result is "chlorosis" often misdiagnosed as iron deficiency. Plants forced to use this salty, alkaline water will dispose of the salts as far away from the roots as possible. This causes the tips of the leaves to burn and become brown and crispy with the salts sometime visible on the leaf surfaces.

Cures: In all cases, water deeply and infrequently, especially if you have clay or caliche soil. Lawns and flowerbeds will need water more often than trees and shrubs so don't mix the types if at all possible.

Deep, infrequent water lets oxygen return to the soil, pushes salts away from the roots, allows nutrient flow and encourages deep rooting. A layer of surface mulch helps a great deal by conserving moisture, cooling and enriching the soil. If you have salt buildup, indicated by a white crust on the soil surface, flush the area thoroughly twice a year. Run drip systems overnight or bubblers for several hours.

Deep, infrequent watering: For most trees and shrubs installed for three years or more, watering once every seven to 10 days in summer and once every 14 to 21 days in winter is enough. Most desert plants need water half that often and newer plants may need it twice as often. If you are fortunate enough to have very good drainage, you'll have to increase watering frequency during the hot months.

If using a drip system, make sure it runs long enough to thoroughly soak the root zone. Running the system two or three times a day for 5 or 10 minutes is wrong and will cause you trouble in the long run. For bubbler systems, run at least 10 to15 minutes for good coverage. For more information, get a copy of "StarNote 900, How Much Should You Water?" from any Star Nursery location or download from the informational Web site at www.starnursery.com.

Improper fertilization will show symptoms in different ways. Over fertilization is evidenced by blackened or scorched leaves, excessive leaf drop and a general unhealthy appearance, even with proper watering. It can also cause overly lush top-heavy growth leading to wind damage and increased insect and fungus attack. Too little fertilizer shows problems through general yellowing of plants, especially on older leaves, small, stunted leaves on tips of branches, weak or spindly growth and little or no fruit or vegetable yield.

Causes: Too much fertilizer, the wrong fertilizer for the season or not enough fertilizer.

Cures: It's easy to over fertilize, especially in hot weather. On the other hand, plants that are undernourished are unhealthy looking and prone to other summer problems like windburn and chlorosis. Make sure to use the right fertilizer for your plants at the right time of year and always follow package directions. A word of advice - if you're not sure, it's better to use too little than too much, especially in desert climates. You can always add a little more but you may kill your plants if you apply too much. If plants show signs of over fertilizing damage, water heavily to remove fertilizer from the root zone and cross your fingers. Over application of fertilizer can also lead to groundwater contamination and environmental problems.

Pay close attention to the time of year a specific fertilizer should be applied. Bag instructions should specify if temperature is a consideration. A mild, balanced fertilizer like 7-7-7 with extra iron is especially effective during the hot summer months while a complete fertilizer, higher in nitrogen like 16-8-4 is better during the active spring and fall growing seasons. Always water plants thoroughly before and after you feed them. Pines, cypress and junipers do best with light, infrequent feeding. When these plants appear yellow, it's usually a sign of over watering or infestation by spider mites.

Other Hot Weather Tips: Don't plant brittle trees in high wind areas. Be sure to properly stake your trees. Improperly staked trees can be damaged by breakage or rubbing bark against stakes. See "StarNote 001, Planting Guide," for illustrations and information on proper tree staking techniques.

When the hot winds blow, and blow they will, plants use more water. Extra watering might help, especially on broad leafed and newly planted specimens. Make sure your sprinkler system is working properly. Take special care to water plants and lawns between the hours of 2 a.m. and 6 a.m. when temperatures are much cooler and winds are less likely to blow.

When working outside in the summer, take time to protect yourself. Wear a wide-brim hat and use plenty of sunscreen. Personal protection is just as important as plant protection.