Answer: Perennials for clay soil are much fewer in number than those that demand good drainage. The problem with clay is that it holds moisture and this tends to rot out the roots of all but the toughest of plants. You can improve your clay soil by incorporating lots of organic matter but failing that, here are some plants that will tolerate clay soil:
Aconitum or monkshood is a classic lover of heavier soils. Alcea or Hollyhocks surprisingly grow well on clay soils. Amsonia should do well on clay.
Anchusa is good once established and protected from slugs (slugs like damper soils and they love anchusa). Anemone are excellent perennials for clay soils and will thrive and flower well on clay. Asters will grow anywhere. Bergenia should be fine.
Brunnera macrophylla should do well although I?m not sure about the newer hybrids ? you?ll have to trial them.
Campanula the taller species do better than shorter, so do C persificolia. You?ll find variations between varieties. ?Loddon?s Pink apparently does well but ?Telham Beauty? is variable.Chrysanthemum (Shasta Daisies) do well enough although they will be shorter-lived on clay than in well drained soils. Coreopsis verticillata is the best in clay. Digitalis or foxglove and Echinops make good clay soil plants.
Geranium: most of the geraniums will tolerate clay soils. Helenium are very showy daisies and they will grow handsomely on clay soils. Helianthemum or perennial sunflowers will grow nicely, Heliopsis is another of the perennial sunflowers and it too grows well in clay.
Hellebore surprisingly enough are listed as surviving quite nicely. Hemerocallis are great on clay. They do take a little longer to become established. Heuchera are great perennials for clay soils and works in a semi shaded ares. Iris germanica or flag iris will grow on heavier ground although many of the species iris will not.
Kniphofia will tolerate clay, Lysimachia will tolerate heavy soils as well. Lythrum will do quite nicely; Monarda or beebalm survive and thrive on the regular moisture of clay. Rudbeckia believe it or not, the biennial forms will live on clay as will the taller species such as ?Herbstonne? and even the most popular ?Goldsturm? will be fine.
Be sure to place the sun lovers in the sun and the shade or semi shade lovers where they get protection from hot afternoon sunshine. Best wishes with your garden!
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