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Give Rhododendrons and ­Mountain Laurels a Head Start

Pluck off wilted flowers

For more abundant flowers on your rhododendrons and mountain laurels next year, deadhead this year’s flowers as soon as they wilt. By preventing the flowers from setting seeds, you’ll stimulate the branches to flush new growth from waiting latent buds. This is especially true if the bushes are growing in full sun.  
    Producing seeds requires considerable energy. Removing wilted florets allows more energy produced by photosynthesis to stimulate the vegetative buds — located at the terminal end of the branches just below the flower buds — into active growth.  
    The active development of vegetative buds in spring-flowering plants is controlled by chemicals known as cytokinin located in the terminal flower buds in rhododendrons and mountain laurels. In other plants, cytokinin resides in the apical bud of each branch. Thus, the terminal bud, whether flower or vegetative — at the end of the branch is generally the first to initiate growth in spring. The vegetative buds farther down each branch wait to grow until after the terminal bud has initiated growth or has flowered and produced seeds. Lower buds remain quiescent even though dormant conditions have been satisfied by cold temperatures.
    Apical dominance, as the phenomenon is called, is common to all woody plants. Understanding how it functions gives you better control over the vegetative growth of your plants as you prune and shear plants to the shape you desire or to promote flowering. This knowledge also helps you choose plants according to purpose. Apical dominance makes the privet plant, for example, more adaptable to shearing than the forsythia.
    To deadhead a rhododendron or mountain laurel, grasp the base of the old flower head and give it a sharp bend and twist. Skip pruning tools to avoid spreading the disease Phytophtora cactorum.
    Phytophtora cactorum causes branches to die back starting at the ends, and it spreads easily from contaminated pruning tools. Dipping the pruning tools in rubbing alcohol between cuts is the only sure and effective means of preventing the disease from spreading when using pruners.
    The disease can also enter the plant via wilted florets. Thus, breaking off flower heads as soon as they wilt is a doubly wise practice.

Death to Poison Ivy — But Not Just Yet

    Poison ivy is one tough plant. The rash-causing oils that coat its lush green leaves also repel water, preventing chemicals from entering their inner tissues. Until the leaves turn from olive to dark green, it is nearly impossible to destroy the roots, which is how most weed killers function. Unless the roots are killed, they will rejuvenate new stems and resume growth.
    Delay your attack until late July to early October, when many leaves are mature and some of the oils have been weathered away. Then mix a spray, as follows, and cover the foliage.
    To kill the pest, you’ll need two chemicals. Glyphosate by itself is only half effective. Add ­ammonium sulfate to help get through the oils and waxes covering the leaves, enabling the glyphosate to penetrate the foliage and enter into the leaf tissues where it will be translocated down to the roots.
    Roundup — the trade name of glyphosate — is available in several concentrations. Add a half-teaspoon of ammonium sulfate to the gallon capacity of the pre-mixed spray. When using the more concentrated forms, read the directions for mixing with water and add one-half teaspoon of ­ammonium sulfate per gallon of spray.