Plants can be fussy about which fertilizer they want

 

By Tony Tomeo

The recent weather certainly has been excellent for gardening! It is so rewarding to see all the flowers from bulbs planted last autumn, and the new seedlings for this year's annuals and vegetables as they start their season.

This is the season when fertilization will be most critical. Fortunately, there is not one single species in the entire plant kingdom capable of reading fertilizer labels. Therefore, it is not important where helpful nutrient supplements come from; however, many species have discriminating tastes. Annuals, fuchsias and bougainvilleas prefer a low-nitrogen complete fertilizer. Too much nitrogen, particularly with the bougainvillea, will promote vigorous vegetative growth, but minimize floral growth. Lawns, citrus and foliage plants, however prefer nitrogen for precisely the same reason. Rhododendrons, azaleas, gardenias and camellias prefer acidifying fertilizer in mild doses, because of their susceptibility to salt burn.

Chlorosis, which is seen as yellowed leaves with green veins, is a symptom of low iron, and may be remedied with iron chelate or iron sulfate rather than fertilizer. Plants in containers prefer half doses every two weeks rather than monthly full doses of fertilizer.

Aphids may have already become a problem in your garden. Although aphids are mobile and some even fly, they are usually "farmed" on new growth by ants. "Honeydew," the sticky fluid excreted by aphids, is a favorite food for the ants. The ants therefore transport aphids to foliar growth most conducive to healthy aphids and the highest production of honeydew. If it is possible to trim infected plant material away from contact with surrounding plant material or structures, and a barrier of any substance impassable to ants, such as lithium grease, is applied around the trunk of the plant, ants will be unable to deliver any aphids.

Aphids already on the plant will eventually be eliminated by natural predators. If the aphid population is extreme, they can be killed instantly with mildly soapy water.

Spider mites also become active in warm weather. Infestation is not as obvious as that of aphids and may first be detected by their damage, seen as a dull raspy appearance to the underside of older foliage. Mites are so small that they may only be seen by close examination. If you suspect their presence, look for small rusty brown specks on the undersides of damaged leaves. Magnification might help.

These specks are mites and might even be seen to be moving around. If the leaves are tapped over white paper the mites will fall onto the paper confirming their presence.

Mites are actually very small relatives of spiders that cannot fly to new host plants. Clearance trimming and sticky barriers will prevent new infestation. They are not killed by soap, but rinsing foliage daily will knock many off. They prefer dusty dry foliage and sometimes infest with ants and aphids because honeydew that is not consumed by ants grows fungus known as "sooty mold," making the foliage about as dusty and dry as it can get. Unfortunately, mites can spend their entire life cycle in their host plant without returning to the soil; so established populations may not necessarily by doomed by isolation. For deciduous plant species, it is best to spray for mites with a light-grade horticultural oil in winter to suffocate their eggs.

However, for evergreen plants, or damaging spring infestations that cannot wait for winter, chemical control may become necessary. In this situation, it is important to remember that mites are actually small spiders and not insects. They must be sprayed with miticides. Most insecticides have no effect on them. It is also important to remember that chemicals can be dangerous, and it is very important to always read labels and use chemicals with caution.

Flower of the Week: Lilac

I can remember when I was very young, the lilacs at my grandmother's home in Santa Clara were the flowers I thought looked and smelled most like spring. As a child, the solar cycle was not important to me. The arrival of spring was determined by the blooming of my grandmother's lilacs.

(Common) lilac, Syringa vulgaris produces very fragrant flower clusters which are excellent for cutting and bringing inside. The classic lilacs are lavender, but are also available in white, pink, blue, purple and purplish red. Some cultivars produce double flowers. The French hybrids are the most available of lilacs and the best suited to our climate. Descanso hybrids also do well here, but are not as available. The unhybridized species is still the greatest; blooming slightly earlier and producing the most fragrant flowers. Unfortunately, it is rather coveted and very difficult to find.

Lilacs are almost always under 15 feet tall with comparable spread. Leaves are soft, light green and usually less than 4 inches long. They prefer to grow in full sun and away from anything that might shelter them from cold winter weather. Exposures that may by useful for protecting frost-sensitive species would inhibit the bloom cycle of lilacs. Lilacs are pruned by a process called "alternating canes" which involves removing a few older canes every year and preserving the young vigorous stems for maximum floral production. Lilacs also prefer alkaline soil; so they are right at home in the Santa Clara Valley.

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Horticulurist Tony Tomeo can be reached at 358-2574.

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