Gardeners often find themselves working with less-than-ideal soil conditions, and the most effective gardeners choose plants that will thrive even under the toughest conditions a site presents. Alkaline soil offers one such gardening challenge by adversely affecting the availability of nutrients to your plants. Because of the challenges posed by an alkaline soil, when selecting shrubs for your home, you should choose those that not only tolerate but thrive under alkaline conditions.
About Alkaline Soil
The pH of alkaline soils measures above 7.0. Most plants, however, prefer a slightly acidic to neutral soil, with a pH between 6.5 and 7.0. As the pH of soil rises, trace minerals needed for plant health become less available. Once the pH rises above 7.5, phosphorus---one of the primary nutrients required for plant health---becomes less available.
Evergreens keep your garden looking vital, even during the bleak winter months, and form a backdrop for your brighter-coloured plants in spring and summer. The University of Minnesota Extension lists several evergreen shrubs as able to thrive in high-pH sites. The mugo pine (Pinus mugo), a dwarf member of the Pine genus, grows between 4 and 10 feet tall, depending on the cultivar. Its dense evergreen foliage persists for years at a time, making it a good selection for planting screens. Arbor vitae (Thuja occidentalis), also called northern white cedar, tolerates anything but shade. Small scalelike leaves cover the sprays of foliage, which can turn brownish during the winter, and cultivars in a range of shapes and sizes can fit nearly any site. The shore juniper (Juniperus conferta) and creeping juniper (J. horizontalis) are small shrubs suited for alkaline sites.
Even more deciduous shrubs will perform well in high-pH soil. For spring-flowering shrubs, the common lilac (Syringa vulgaris), bush cinquefoil (Potentilla fruticosa), buttonbush (Cephalanthus occidentalis) and redosier dogwood (Cornus sericea) will brighten your garden. In addition to its spring flowers, the redosier dogwood offers vivid red fall foliage and red twigs that stand out against winter snow. If you want to grow a deciduous shrub for its foliage, the Japanese barberry (Berberis thunbergii) and common juniper (J. communis) thrive in alkaline soils.
Amending Alkaline Soils
You may lower the pH of your soil by applying organic matter, sulphur or aluminium sulphate. The effects are short-lived, however, and you may need to apply these materials each year to keep the pH low. Because sulphur can damage plant roots, using it around permanent shrub plantings risks damaging your plants. Focusing on alkaline-loving shrubs saves you the trouble of constant soil amendment and the potential for damage.
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- University of Massachusetts Extension: Soil Basics -- Chemical Properties of Soil
- University of Minnesota Extension: Tough Trees and Shrubs for Tough Sites
- University of Florida IFAS Extension: Pinus mugo
- Ohio State University: Thuja occidentalis
- Native Plant Information Network: Cornus sericea L.
- University of Florida IFAS Extension: Soil pH and the Home Landscape or Garden