Plants for Clay Soil: Ground Covers

Our mission is to replace our thirsty lawns with some kind of a ground cover. But what do we mean by "ground cover?" Ground cover can include plants, mulch, semi-permeable granite, vines grown horizontally, and even native grasses (or, more likely, some combination of the above). In fact, some of the low shrubs that I reported on last year qualify as ground covers (see Plants for Clay Soil: Low Shrubs).

This year I'm expanding my search for ground cover plants that thrive in the conditions of our San Francisco Bay Area home - with its clay soil (compacted with lots of tree roots), mixed areas of sun and shade, sloping aspect, and magnificent oak tree. Our small lawn has converted to moss, which I love, but it looks dead most of the year due to our perpetual drought. Low maintenance is desirable.

In my quest, I'm using several sources, including a tool new to me, available at http://www.waterwonk.us/ (free, with a log on account). The tool enables you to search for plants by city or California area, and by categories such as California Native, plant type, and water requirement. One category is California Summer-dry Climate, which uses information in Bob Perry's Landscape Plants for California Gardens. You can download the search results in PDF, or cvs format for use in a spreadsheet. Here are some of my favorite results for our East Bay landscape in the Oakland Hills.

• Achillea millefolium (Common yarrow) – clumping species that forms a dense mat, grown from rhizomes. Can be mown into a law that can withstand some foot traffic, or grown on a slope to control erosion. Grows 18-30 inches high. Foliage is formed of finely divided medium leaves; white flowers in spring. Adapts to various soil types, including clay; prefers full sun. California native species have been introduced as cultivars - A. m. 'Cameo' (salmon flowers), A. m. 'Island Pink' (magenta flowers), and A. m. 'Paprika' (red flowers with yellow centers). Requires low water (does best with regular moisture through late spring, but adjusts to less summer irrigation). Asteraceae family.

• Arctostaphylos uva-ursi (Bearberry or Bayberry, Manzanita) – prostrate, mat-forming, woody perennial vine, 6-12 inches high, spreading 10-12 feet. Dense foliage is formed of small dark glossy green leaves attached to dark red-brown branches. Pink or white inverted urn shaped flowers in late winter, with red berries. Requires full sun to light shade, well-drained, slightly acid sandy soil. Plants are sensitive to foot traffic. California native cultivars include A. u. 'Point Reyes' and A. u. 'Green Supreme'. Requires very low water. Ericaceae family.
  
  
  

  

  Bearberry – ground cover
  Photo posted by Daderot (Creative Commons).

   Artemisia californica (California sagebrush, Artemisia) – low rounded form, 3-5 feet high, with 5-7 feet spread, comprised of herbaceous stems and foliage. Silver-gray, fine textured foliage with pungent aroma, and insignificant flowers. Coastal sage plant community that performs well in sun, heat, and drought (may become partially deciduous in extreme drought). Often used in restoration projects. California native cultivars with prostrate habits include A. c. 'Canyon Gray' and A. c. 'Montara'. Requires very low water. Asteraceae family.

• Baccharis pilularis (Dwarf coyote brush) – evergreen, coastal shrub. Foliage consists of small green leaves up to 1/2 inches, with undulating to randomly toothed margins. Plants are dioecious. Male shrubs are recommended; female shrubs have insignificant flowers and messy seed pappi, which require maintenance. Often used in revegatation projects. California native cultivars include B. p. 'Pigeon Point' and B.p. 'Twin Peaks'. Both have a prostate form, and are well suited to slopes and sun near the coast. Requires low water. Asteraceae family.

• Ceanothus gloriosus 'Anchor Bay' (Point Reyes ceanothus) – spreading evergreen mounding shrub, native to Pacific coast. Grows 12-24 inches high, with 6 feet spread. Thick, dark green, 1 - 2 inch leaves with heavily toothed margins. Clusters of tiny blue flowers in early to mid-spring. Requires full sun, and well-drained rocky soil. Subject to root rot if too moist. This California native cultivar is excellent for slopes or banks in coastal zones. Requires low water. Rhamnaceae family.

• Ceanothus thyrsiflorus var. griseus 'Diamond Heights (Diamond Heights ceanothus) – very unique, prostrate California native cultivar with striking yellow and lime-green foliage; insignificant flowers. Grows to 12 inches high, with 3-5 feet spread. Lacks the vigor and reliability of some cultivars, especially in warmer and drier climate zones. Requires low water. Rhamnaceae family.

• Eriogonum fasciculatum (Common buckwheat) – densely branched shrub grows 2-3 feet high, and as wide. Foliage is prickly, needle-like leaves; flowers are white to light pink in late spring. Grows in the coastal sage scrub plant communities in bluffs. Adaptable to many types of soil in its range, and to heat, and dry conditions. Provides pollen for bees, and seeds for birds. Used to stabilize slopes, and restore natural areas. California native prostrate cultivars include 'Theodore Payne' or 'Warriner Lytle' Requires low water. Polygonaceae family.

• Iva hayesiana (Hayes iva, poverty weed) – low growing evergreen shrub grows 2-3 feet high, and 4-5 feet across. Foliage is comprised of pale green aromatic leaves 2-3 inches across; flowers and fruit are inconspicuous. Tolerates sun and various soil types, including clay and alkaline, with very little care. Used on slopes for erosion control. In the landscape, may look better if trimmed to 12-18 high in the fall to look more uniform as a ground cover. California native; requires very low water. Asteraceae family.

• Salvia sonomensis (Creeping sage) – prostrate perennial herb grows 8-12 inches high with 3-4 feet spread. Leaves are pungent, olive green, and rough textured; flowers are lavender blue on 4-6 inch high spikes above the foliage in spring to early summer. Commonly grows in the chaparral, and yellow pine forest plant communities in the understory. In the landscape it grows best in sunny locations, on well-drained soils with little extra water. Grows well on slopes and banks. California native; requires low water. Lamiaceae family.

• Salvia spathacoa cvs. (Hummingbird sage, Pitcher sage) – small clumping perennial grows 12-18 inches high, and as wide from below-ground rhizomes. Large deep green leaves 4-6 inches long; spikes with deep magenta-red flowers in early spring. Grows as an understory plant to native oaks, and on grassy slopes in the southern oak woodland plant community. Attracts hummingbirds. California native; requires low water (leaves and stems may die back under drought stress). Lamiaceae family.

Good sources:

• Annie’s Annuals and Perennials: http://www.anniesannuals.com/
• Bay Natives: http://www.baynatives.com/
• Berkeley Horticultural Nursery: http://berkeleyhort.com/index.html
• California Flora Nursery (no mail order, but located 63 miles north of Oakland/Berkeley): http://www.calfloranursery.com/
• Desert Mountain Conservation & Development Council (no mail order, but pick up in designated location, and on designated date and time): http://desertmountainrcandd.org/
• Las Pilitas Nursery (Santa Margarita): http://www.laspilitas.com/
• The Watershed Nursery : http://www.watershednursery.com/