Many chalky soils are shallow, very free-draining and low in fertility, but variations exist. Where there is clay present, nutrient levels may be higher and the water holding capacity greater.
Where chalky soils are deep, they can be moisture-retentive and support a wide range of plants. They will not support ericaceous plants such as camellia and rhododendrons that need acid soil conditions. Very chalky soils may contain lumps of visible chalky white stone. Such soils cannot be acidified, and it is better to choose plants that will thrive in alkaline conditions.
When planting on chalky soils it is important to first establish how deep the topsoil is. Many trees and shrubs that will tolerate alkaline soil conditions may become chlorotic (yellow) on shallow soils over chalks. In some gardens the soil layer may be very thin indeed – only a few inches – before hitting solid chalk. Where this is the case, topsoil will need to be brought in to make planting possible. On shallow soils over chalk where increasing soil depth is not an option, wildflower mixes selected for chalk tolerance may still thrive.