Northstate residents prize large trees for their beauty and the shade they provide.  There are other environmental benefits to mature trees as well.  They encourage biodiversity, offset carbon emissions, and reduce energy costs for the homeowner. 

Shade trees also create a challenging environment for many landscape plants the home gardener may want to grow beneath their boughs.  Light and moisture, basic growth requirements for all plants, are often limited under trees.  The very shade that cools yards in the summer also restricts plant growth.  The soil beneath mature trees is often dry and choked with water absorbing roots.  For understory plants to thrive, these obstacles must be overcome.

If trees are deciduous, their shade is seasonal and the success of what is planted beneath them may be dependent upon how early the trees leaf out and the density of their canopies.  To open the canopy of a deciduous tree so that it casts lighter shade, prune it late in winter.  This way, not only is the tree dormant, but its branch structure is completely visible and can be thinned while maintaining the overall shape of the tree.  To allow sunlight to penetrate to the base of dense evergreens, remove their lower limbs to a height of at least eight feet above the ground.

A tree's roots tend to aggressively snatch every drop of water from the soil, leaving little or no water for understory plants growing beneath it.  A solution to this problem is to irrigate adequately to meet the tree's and the understory plant's needs.  Another approach is to grow desired understory plants in pots (with saucers) or in raised beds, so that the plants aren't in direct competition with trees for water.  If you opt for raised beds, it's a good idea to provide a gap of a few inches between the bottom of the bed and the ground.  If the bed is in direct contact with soil, tree roots may invade it and defeat the purpose of the bed.  Also, if a raised bed is in contact with the soil, it could interfere with the uptake of the oxygen the tree roots need to survive.  To conserve water, installing an automated watering system using drip irrigation or soaker hoses, rather than sprinklers, is recommended. 

Shade-loving plants are physiologically adapted to getting by with less light than sun-lovers.  When you go to a local nursery to buy plants for a shade garden, check their labels.  Plants that are labeled “shade tolerant” or “part shade” prefer 4-6 hours of sun per day.  All plants need light, so a plant labeled shade, or “full shade,” doesn't mean “no sun.”  Rather, these plants prefer less than 4 hours of sun and may actually burn if exposed to more sun, especially in the afternoon. 

The following is a partial list of plants that will do well in shade gardens in our area.  Those with an asterisk* are California native plants.  Natives tend to be less thirsty, better adapted to our climate and beneficial to wildlife.

Part shade (4 to 6 hours of sun per day): 

Agapanthus (Agapanthus sp.), Azaleas (Rhododendron indicum), Santa Barbara daisy (Erigeron karvinskianus), Bush anemone* (Carpenteria californica), Chaparral currant* (Ribes malvaceum), Yarrow* (Achillea millefolium), Douglas iris* (Iris douglasiana), Hummingbird sage* (Salvia spathacea), Idaho fescue* (Festuca idahoensis), Rosy buckwheat* (Eriogonum grande var. rubescens), Coffee berry* (Frangula californica), Woodland strawberry* (Fragaria vesca)

Full Shade (less than 4 hours of sun per day):

Hellebore (Helleborus sp.), Pigsqueak (Bergenia crassifolia), Creeping Oregon grape* (Mahonia repens), Evergreen currant* (Ribes viburnifolium), Snowberry* (Symphoricarpos albus), Spicebush* (Calycanthus occidentalis), Western columbine* (Aquilegia formosa)

Additionally, almost all ferns sold in local nurseries will do well in shade or partial shade.  Check the label to be sure.

UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system. To learn more about us and our upcoming events, and for help with gardening in our area, visit our website. If you have a gardening question or problem, email the Hotline at mgbutte@ucanr.edu (preferred) or call (530) 538-7201.