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.