University of Vermont Extension
Department of Plant and Soil Science


Landscape Gardening on Clay          OH 31

Leonard Perry, Extension Professor

Clay soils present a difficult growth environment for most plants. Because of the water-holding nature of clay, sufficient air does not reach the plant's roots, thus limiting its growth. Plants that begin as wild seeds in clay can sometimes develop appropriate root systems and survive. Nursery-grown trees and shrubs, however, cannot adjust to clay soils, even over several years.

Certain precautions can be taken if you must plant in clay soils. Select rolling or sloping areas if possible, and be sure that downspouts and drains are diverted from plantings onto driveways or lawns. Do not consider planting ornamentals known to prefer sandy loam until suitable soils can be prepared for them.

Preparing a Suitable Soil

For tough, raw or compacted clay, work soil conditioners into the ground as far as a power tiller can go; include fresh or composted gypsum and organic matters of all kinds. If planting can be delayed from fall to spring, sow winter rye as a green manure crop to turn under in April.

Where clay is too hard to work down into, add clay loam to raise beds and slope the sides gently to meet the surrounding grades. In limited spaces, place landscape timbers as much as 12 to 18 inches high around the planting area, and fill with good growing soil mix, compacted to 1 inch from the top.

For flush or near flush beds, deep tillage preparation is essential as heavy roots may descend more than 20 inches and must have perfect drainage all the way. An array of shrubs and trees will succeed, along with a fine selection of perennials, when abundant organic compost and mulches are used. In sunny gardens, peonies and roses (hybrid teas in particular) are ideal.

 



Trees and shrubs that generally do well in heavy, wet and clay soil

Shrubs Trees
Arborvitaes Lilacs Ash Honeylocust
Barberries Mockorange Beech Linden (basswood)
Bayberry Potentilla Birch (while young) Maple, Norway
Burning-bush Privets Concolor fir Maple, sugar or hard
Cotoneasters Viburnums Crabapples, flowering Mountain ash
Dogwood Weigela Ginkgo Oaks
Flowering quince Willow, pussy Hawthorns Walnut
Forsythia Winterberry
Honeysuckle Witch hazel
Hydrangea Yews

Trees are the most difficult to establish in plantings flush with surrounding areas. Small trees, from seedling on up, in bare root stock with shallow roots are most successful. It may take up to 10 years or more for larger trees to become well established with surface roots sufficient to survive a short flooding.

Standard herbaceous garden plants demand rapid drainage at all times. Raise or crown such planting beds in flat areas, or supply subsurface drainage pipes. A well-balanced border requires plants from widely varying soil types; clay loam is most satisfactory when it is well loosened with abundant compost and peat for individual plant needs. These plants may multiply much faster than usual and need dividing and replanting more often.

Spring-flowering bulbs are dormant in the summer; they must have fairly dry conditions from June to September. Where used among perennials, bulbs should be set on a 1-inch pad of coarse sand with several inches of good soil below. Borders with bulbs are best kept cultivated with a loose soil mulch to avoid frequent waterings. More information on mulches can be found in GL 6, "Organic Mulches."


Return to Perry's Perennial Consumer Page

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. Lawrence Forcier, Director, UVM Extension System, Burlington, Vermont. University of Vermont Extension System and U.S. Department of Agriculture cooperating, offer education and employment to everyone, without regard to race, color, national origin, sex, religion, age, disability, political beliefs, and marital or familial status.

Last reviewed 2003