By adding a few drops of cider vinegar to a soil sample,
you can test the alkalinity of the soil. If it fizzes the soil
is alkaline, or use a home test kit. To reduce alkalinity
add acidic materials such as peat moss, sulfur, or
aluminum sulphate to your soil. Add 2.5kg(5lb) of peat
moss, 350g to 1kg(¾-2½lb) of sulfur, or
2.5 to 7kg(5-15lb) of aluminum sulphate per 9m²
(100ft²) to lower the ph by one unit. Use smaller
amounts of additives in sandy soils and larger amounts
in heaver (clay) soils. By improving drainage you may
help reduce alkalinity by allowing water to wash through
and carry away alkaline salts. Place plenty of dead
leaves, compost material and other organic matter into
the bottom of planting holes. Coffee grounds also help
to reduce alkalinity too. Dig a good helping into the soil.
Spreading a organic mulch on the ground like a blanket
prevents surface evaporation of water and the build-up
of alkaline salts. Use straw or dead leaves. Some
desirable flowering plants that like it best in a alkaline
soil include Madonna lily, purple cone flower, candy
tuft, and phlox. Some alkalinity loving shrubs include
lilac, juniper, hawthorn, peas shrub, and Russian olive.