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.