Shrubs are integral components of a home landscape. Shrubs can be used as hedges, screens, barriers, groundcovers, foundation plantings, and backgrounds for other plants. They can also be used as accent or specimen plants. Shrubs also provide food and shelter for birds and wildlife.
When selecting shrubs for the home landscape, gardeners should carefully examine growing conditions at the site. Important site conditions include soil drainage, soil pH, and the amount of sunlight.
Most shrubs grow well in soils with a pH of 6.0 to 7.5. Since the pH of most landscape soils in Iowa falls within this range, soil pH is generally not a problem. However, there are exceptions. Rhododendrons require strongly acidic soils with a pH of 4.5 to 5.5. Home gardeners can lower their soil pH by incorporating Canadian sphagnum peat into the soil. Sulfur can also be used to lower soil pH.
Well-drained soils are preferred by most shrubs. In poorly-drained sites, gardeners can build berms or raised beds. Buttonbush, redosier dogwood, and goat willow are good choices for wet, poorly-drained soils.
Many flowering shrubs, such as lilac, spirea, and weigela bloom best when grown in areas that receive at least 6 to 8 hours of direct sun each day. Others, such as Amur maple and winged eounymus, develop their best fall color when grown in full sun. Partially shaded sites that receive only 2 to 3 hours of sun are suitable for common witchhazel, Japanese kerria, and arrowwood viburnum.
Plant characteristics are also important when selecting shrubs for the home landscape. Important plant characteristics include size, hardiness, ornamental characteristics, and susceptibility to insects and diseases.
The mature height and spread of shrubs vary somewhat due to growing conditions at the site. However, knowledge of their approximate size can prevent overcrowding and other landscape problems. Shrubs that are too large for the site require frequent pruning. Others end up being moved or destroyed.
Iowa occupies USDA Hardiness Zones 4 and 5. The average minimum temperature in Zone 4 is -20 to -30 F. The average minimum temperature in Zone 5 is -10 to -20 F. Select shrubs that are reliably hardy in your area. It may be possible to grow plants that are marginally hardy in your area (Zone 5 plants in Zone 4) if planted in protected areas, such as courtyards.
Many shrubs have attractive flowers, fruits, foliage, or bark. Some shrubs are rather one dimensional. For example, forsythias have attractive yellow flowers in early spring, but provide little ornamental interest the remainder of the year. Other shrubs possess several ornamental features and provide multi-seasonal interest.
Susceptibility to insects and diseases is another important consideration when selecting shrubs. No shrub is completely free of insect or disease pests. However, avoid those that have serious problems.
This article originally appeared in the 5/11/2005 issue.