The depth at which you plant can have a great impact on growth. Most plants, including shrubs and perennials, should be planted at the same depth as they were in their pots. However, there are exceptions, including those mentioned below. Most trees also have specific planting needs.
Some plants perform best when planted slightly above the surrounding soil level. These include irises, whose rhizomes (bulblike structures) will rot if buried, and other plants sensitive to wet soils, including Verbascum, Sisyrinchium, Sedum, and other hardy succulents.
Plant these 1 in (2–3 cm) above the surface, leaving iris rhizomes exposed; for other plants, raise the soil in a mound around the rootball, so that water drains off.
Moisture-loving plants often prefer to be planted more deeply in the soil, so that their roots are not exposed to the drier conditions near the surface. Plant hostas with their roots 1 in (2 cm) below the surface, and bury Solomon’s seal (Polygonatum) at a depth of 4 in (10cm).
Tips: Teasing out roots
When planting, you may see the roots growing around in a tight circle, where they have been restricted by the pot. This is known as “root-bound,” and will limit the plant’s development. Remedy the problem by gently teasing out the roots so that they will grow away from the ball into the surrounding soil.