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March Q & A
By Michelle Le Strange, UC Master Gardener Advisor
Q. Several of my bushes, especially azaleas, are just about to bloom, but the leaves are all yellow. Is this chlorosis?A. Chlorosis is like anemia, if you're a plant. When leaves are yellow between the veins, it usually means that plants are iron deficient. You'll notice it first on new plant growth.
Iron chlorosis is common in alkaline soils, and alkaline soils are common in the valley. It's not that these soils don't have iron, on the contrary, they do. It's just that the iron is "locked up" as an insoluble compound and unavailable to plant roots. Acid-loving plants like camellias and azaleas are quick to show yellow leaves, especially when soils are soggy wet.
Just as anemia requires the right type of iron pill, so does chlorosis. Treat the soil with iron sulfate or with iron chelate. Chelated iron may cost more, but it keeps the iron in a soluble form that plants can use. Chelated iron mixed and sprayed on plant leaves is easily absorbed, and soon foliage greens up. Other iron fertilizers also work but not as fast, and repeated applications are needed.
Q. Our new home is landscaped in the front, but the backyard is completely empty. Where should we start?
A. First develop a plan. Make a quick analysis of the site, checking for natural drainage and slope. Grade soil so water moves away from the house and wooden fences.
Determine the sunny and shady locations throughout the day, and be sure to include the shadows cast by the north, south, east, and west walls of the house. Plan for solar penetration and protection. Where do you need sun or shade and at what times of the year? Deciduous trees provide summer shade and allow sun penetration during winter. Evergreens provide year-round shade and screens but prevent sun penetration. For afternoon shade in the summer, plant trees south and west of the target shade zone.
Locate your patio and pathways. Don't stop at just getting the lawnmower from the garage to the lawn. Consider how you are going to step around the entire perimeter in your slippers or good shoes without getting them wet or dirty.
Plan for pleasing views from favorite windows or outdoor seating areas.
Now concentrate on the major elements first and keep the plan simple. Many beautiful yards are just a combination of a few trees, a couple of groundcovers (including a lawn), and an evergreen hedge that screens undesirable views and provides privacy.
Once the essentials are out of the way, then you can elaborate with special areas for fragrant and colorful plants, herbs and vegetables, and maybe even an espaliered fruit tree for effect.
Q. Each spring the big ash trees in my front yard leaf out, then a couple of weeks later the leaves develop brown blotches and fall off. What causes this?
A. Anthracnose is a disease found on many deciduous and evergreen shrubs, particularly sycamore, ash, and evergreen elms. Infections are most severe when spring rains are continuous while leaves are developing. Anthracnose fungi need water to spread; they don't spread under dry conditions. The disease usually starts on bottom branches and then moves up the tree.
When trees are heavily infested with anthracnose, they drop their leaves prematurely. If trees have had the disease for many years, they can be completely defoliated, but most branches recover and produce a new crop of leaves.
Once symptoms develop, anthracnose cannot be effectively controlled. Pesticides can work on Modesto ash trees, but spraying huge trees regularly is not practical. Pruning helps reduce the disease inoculum for next year.
March 16, 2000
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