Volume 16, Issue 32 - August 7 - August 13, 2008



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The Bay Gardener by Dr. Frank Gouin


It’s Azalea Planting Time

Get these acid-loving plants in the ground while their roots will have time to grow

August and early September are the best time for transplanting azaleas, rhododendrons, mountain laurel, leucothoe, andromeda and blueberries. These acid-soil-loving species transplant best at this time of year because their tops stop growing, which means that they concentrate their available energy in growing roots. These woody species don’t grow roots and tops at the same time. When the tops of the plants are growing, the function of the roots is to supply the tops with adequate water and nutrients. When the top stops growing, it is then time for the leaves to produce the necessary energy, through photosynthesis, for the roots to grow in preparation for next year’s spring flowering and growth.

Success in transplanting these acid-loving plants also depends on knowing something about their roots and soil requirements. All have very shallow roots and will only thrive in a well-drained soil. This means that you never dig the hole so deep that the roots are covered with soil. Only dig the planting hole sufficiently deep so that the top of the root ball will be visible after planting.

If the plant has been growing in a container, remove the container and examine the root ball. If the root ball is surrounded by a mass of roots, take a sharp knife and slash the outside layer of roots approximately one inch deep from the top to the bottom of the root ball. Never transplant a root-bound plant without disturbing the roots if you want that plant to survive.

Another cultural requirement to consider when transplanting acid-loving species is that you will be transplanting these plants in a soil with minimal amounts of calcium and magnesium. These species grow best in a soil having a pH of near 5.0. If your soil test results indicate soil pH of 6.0 or above, you will have problems. However, at a soil pH of 5.0 you will find that the plants will greatly benefit from amending the soil with a handful of gypsum in the back-fill. Gypsum is calcium sulfate, which makes calcium instantly available for rapid root growth. If your soil test also indicates that magnesium is low, blending a tablespoon of Epsom salts with the gypsum will do wonders.

Keep Your Elements Straight

Q Our soil test report advised adding Borax. Can we change out the Borax for Epsom salts? We understand that Borax is poisonous and will kill earthworms.

–Joseph Gondolfo, by email

A Borax at the recommended rate will not harm worms, but it is boron, an essential trace element, that is found in most soils. Epsom salts are magnesium, not boron.

Ask Dr. Gouin your questions at frgouin@erols.com. All questions will appear in Bay Weekly. Please include your name and address.

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