This group includes plants that cannot tolerate limestone (chalk) and need acidic soils to grow normally, this is soil, of which pH must lower tahn 6. According to pH value (acidity and alkalinity), soil can be either acidic, neutral or alkaline, with intermediate levels. Fertile, quality garden soils of most gardens and parks are slightly acidic to neutral (pH 6-7) and suit most of plants. If soil contains a lot of calcium (limy soils), it is alkaline soil. Acidic soils contain much less calcium, they can be richer in humus. Some acidic soils are washed out and poor in plant nutrients. Plants like, for example most of the rhododendrons, heather, camelias and bluberries, grow normally only in distinctively acidic soils, so such soil must be attained when planting. Most of other plants do grow well in slightly acidic soils, but grow as well also in neutral soils with a bit higher calcium content.