By Ellen Barcel
Long Island is primarily a large sandbar — something that gardeners have had to deal with by adding topsoil, compost, etc. But, what if you are one of the minority who has some clay soil? There are basically two things you need to do. One is to amend the soil for optimum plant grown. The other is to select plants that do well in heavy clay soil.
Amending clay soil
Many people assume that the best way to improve clay soil is to add sand to it. Wrong! Think about what bricks are made of — yes, clay and sand. The best way to amend clay soil is to add organic matter, like lots of compost, to it. Compost helps aerate clay soil and encourages it to drain. You can also add aged manure or straw.
Along this same line, when you mulch, use organic material since it will break down into compost. A gardening friend of mine also mentioned that clay soil is very heavy and can be very difficult to dig into. Because you need strength, you may need help.
Test the soil pH and see if it is compatible with the plants you wish to grow in that area. If it’s too acidic, then add lime. Remember that once you start changing the pH (either making it more or less acidic), it is something you must do on an annual basis.
Old-fashioned Hydrangea macrophylla will be blue in acidic soil and more purple or pink as the soil becomes more alkaline. People who buy these older pink hydrangeas and don’t add lime to their soil periodically will wind up with blue hydrangeas in a few years as the plants react to the more acidic soil.
When selecting plants for clay soil, remember that you must also take into account the usual considerations: How much sunlight does the area receive? Does the area flood periodically? Does the area not drain well at all? Does the area receive a lot of salt spray? Are the plants in the area exposed to air pollution as can be found along busy roadways?
Rule of thumb — if, when you are researching plants, the source notes that those particular plants like well-drained soil, they probably will not do well in clay soil. Another observation when selecting plants: If you want plants that don’t do well in clay soil, consider planting them in containers that you fill with a good-quality potting soil.
The following are plants to consider for clay soil:
• Shrubs: weigela, forsythia (blooms in early spring), flowering quince (slow growing, blooms in spring), roses (sun loving), hydrangeas (partial shade, water loving so do well if the location is slow to drain).
• Veggies: shallow rooted such as lettuce, snap beans, broccoli, cabbage and scarlet runner beans (Phaseolus coccineus), which are raised primarily for their abundance of red flowers.
• Annuals and herbaceous perennials: asters, black-eyed Susans, daylilies, cannas (tender bulls, plant in spring), coreopsis (deer resistant), purple coneflowers (deer resistant), perennial geraniums (deer resistant), bee balm, a.k.a monarda (attractive to butterflies), irises (plant in fall), hostas (shade loving, come in a wide variety of sizes from tiny for rock gardens to enormous and colors from green to yellow and blue leaves), ferns (ideal for shade gardens).
• Grasses: Miscanthus — ornamental grasses such as fountain grass, silver grass, pampas grass, etc. Ornamental grasses do best in a sunny location.
• Trees: eastern pin oak (oaks do very well on Long Island with its acidic soil), ginkgo (“fossil” tree, known to be pollution resistant, plant male trees unless you want the fruit).
Ellen Barcel is a freelance writer and master gardener. To reach Cornell Cooperative Extension and its Master Gardener program, call 631-727-7850.