Soil pH

The science of gardening... so much to learn!  Soil pH is a measure of the soil acidity or soil alkalinity. An acid solution has a pH value less than 7.  The majority of food crops prefer a neutral or slightly acidic soil (pH 7).  Some plants, however, prefer more acidic (e.g., potatoes, strawberries) or alkaline (e.g., brassicas) conditions.  Soil pH is an important consideration for farmers and gardeners for several reasons:

• Many plants and soil life forms have a preference for either alkaline or acidic conditions, affecting the choice of crop or plant that can be grown without intervention to adjust the pH
• Diseases affecting plants also tend to thrive in soil with a particular pH range
• The pH can affect the availability of nutrients in the soil. 

Examples of plant preferences

Acid soil of pH 4.5-5.0 Some plants will not tolerate higher pH such as Blueberry, Bilberry, Heather, Cranberry, Orchid, Azalea, for blue Hydrangea (less acidic for pink) , Sweet Gum, Pin Oak.

Acid soil of pH 5.0 - 5.5 Plants for acid soil in this range include Parsley, Potato, Tomato, Heather, Conifers, Pine, Sweet Potato, Maize, Millet, Oars, Tye, Radish, Ferns, Iris, Orchids, Rhododendron, Camellia, Daphne and Boronia.

Acid soil of pH 5.5 - 6.0 Plants for a moderately acid soil include Bean, Brussels Sprouts, Carrot, Choko, Endive, Kohl Rabi, Peanuts, Rhubarb, Soyabean, Crimson Clover, Aster, Begonia, Canna, Daffodil, Jonquil, Larkspur, Petunia, Primrose, Violet and most bulbs.

Acid soil of pH 6.0 - 6.5 Plants that prefer this soil include Broccoli, Cabbage, Cauliflower, Cucumber, Egg Plant, Pea, Sweet Corn, Pumpkin, Squash, Turnip, Red Clover, Sweet Clover, White Clover, Candytuft, Gladiolus, Iceland Poppy, Pansy, Rose, Snapdragon, Viola, Wallflower, Zinnea and Strawberry.

Acid soil of pH 6.5 - 7.0 Plants that favor very mildly acid soil are Asparagus, Beet, Celery, Lettuce, Melons, Onion, Parsnip, Spinach, Lucerne, Carnation, Chrysanthemum, Dahlia, Stock, Sweet Pea and Tulip.

http://en.wikipedia.org/wiki/Soil_pH