Flowers, groundcovers, and bulbs usually are placed into a cultivated bed rather than in individual holes. This permits them to be installed with a hand trowel, hoe, or bulb planter rather than with a spade. Preparation of the planting site may be done using a spading fork, shovel, or a garden tiller. Except in areas where the water table is high or the drainage very poor, adequate drainage for successful establishment of flowers and groundcovers can be attained by incorporating quantities of sand and organic matter into the soil at the time of bed preparation.
Trees and shrubs require differing site preparations depending on their size and the form of their root systems. Much has been discovered by horticulture researchers in recent years that is contrary to long established industry practices. The objective of the landscaper should be to make the planting hole the correct size to meet the needs of the plant as measured by its root form and the soil structure at the planting site. On sites where the soil structure is good and drainage adequate, the planting hole should be just deep enough to contain the root system, allowing it to rest on undisturbed soil with the top of the root ball two or more inches above the top edge of the planting hole. Where drainage is poor, the root ball should be set even higher (Figure 10-4). For bare root plants, the hole should be deep enough to contain the root system without it becoming wadded. In all cases, the plants are set high to allow for settling that will usually occur over time after several waterings. It also helps prevent water from collecting around the trunk and promoting disease.
The width of the planting hole will also vary from site to site. For bare root plants, the width need be only enough to prevent crowding. For balled and burlapped and containerized plants, the planting hole should be at least twice as wide as the soil ball. The same applies to the width of trenches used for hedge plantings. On sites where the soil is highly compacted, such as former building sites, the width of the planting hole should be increased to three or more times the diameter of the soil ball.
All soils, especially those that are compacted or have a high clay content, are likely to become glazed along the sides of a planting hole. Glazing can prevent the roots from growing into the surrounding soil. When the hole is created mechanically, as with an auger or a tree spade, the probability of glazing is even greater. Therefore, the sides and bottom of the planting hole should be loosened (scarified) before the plant is set. Scarification can be done with a spade, hoe, or steel rake.
figure 10-4. The finished planting (Delmar/Cengage Learning. Photo by Jack Ingels.)