Trees and shrubs need good, fertile, moist – but well-drained – soil. Some types tolerate wet, heavy soil and others enjoy warm, dry soil. Thus a choice can be made for any soil type.
It is not practical to improve the soil for trees and large shrubs, because their root area is just too large, but proper planting will greatly help establishment. The soil area for smaller plants can be improved by digging in well-rotted manure, compost or peat and some general fertiliser, before planting.
The acidity of soil can affect trees and shrubs. Very acid, peaty soil causes poor growth because the soil is low in available plant nutrients while limy soil causes some of the best garden shrubs – rhododendrons, camellias and heathers – to fail during to iron deficiency, iron becoming unavailable to these plants when grown in limy soil.
Slightly acid conditions, pH 6.5, are ideal for a wide range of plants. Hydrangeas are good indicator plants, carrying pink or red flowers on limy soils, blue on acid and a weak purple on neutral soils. Soil test kits are available and adequately accurate for most ordinary garden use.