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Plants Have Different Tastes

How to grow a garden to suit many tastes

Quite a few plants love acid soils. Andromeda, azaleas, blueberries, leucothoe, mountain laurel and rhododendrons, bald and pond cypress, deciduous hollies, false heather, heather, Japanese hollies, mountain silverbell, oaks, partridge berry and sour gum love acid soils.
    Such plants demand soil with a pH between 4.5 and 5.5.

Where to Go for Soil Testing

Q    I enjoy your column in Bay Weekly. I wanted to send a few soil samples out to get tested from my vegetable garden. Please take a minute to give me the name and email address.
    –Mike Morgan, Bowie

A    Go to, where you will see instructions and forms. If your soil is sandy, get the S3 test.

Ask Dr. Gouin your questions at [email protected]. All questions will appear in Bay Weekly. Please include your name and address.

    Their chemistry explains why they perform best in acid soils. Azaleas to sour gum absorb most of their nitrogen in its ammonium form, which is how most nitrogen exists in acid soils. As soil pH increases above 5.5, some of the nitrogen is converted to nitrate nitrogen. Nitrate nitrogen is not acceptable to acid-loving species, though it is readily absorbed by other species.
    When the pH drops below 4.0, aluminum becomes available. That element is toxic to the roots of most plants. Thus it is possible to have soils that are too acid, as can happen if you use acid fertilizers for prolonged periods without having your soil tested.
    The vast majority of horticultural plants prefer almost neutral soils with pHs between 5.5 and 7.0.
    If you want both sorts in one garden, what should you do?
    For acid-loving plants to co-exist with other species in the same garden, you must increase the organic matter in your planting soils. By adding sufficient compost to increase the organic matter concentration to five percent and higher, it is possible to have azaleas and other related species growing side by side with junipers, taxus, viburnums and other plants that want neutral soils. This method is used with great regularity by landscape architects and horticulturists in establishing landscapes.
    A high concentration of organic matter guarantees an abundant supply of humic acid, and the natural decomposition of organic matter assures an abundant supply of ammonium.
    Mulch with compost to maintain the level of organic matter.
    Compost mulch not only provides organic matter but also supplies all of the essentials for plant growth. Bark mulch provides few plant nutrients. Furthermore repeated application of bark mulch results in suffocation of shallow-rooted acid-loving species. This is one reason why we often see a decline in growth of some species and overpowering growth of deep-rooted species that do not depend on surface oxygen.