by Dave Waltzer
If you live in any of the rural areas of Santa Cruz county, there is a very high likelihood that you will be faced with the problem of what to grow in the shade. If you live in an oak woodland, there are more plant options, but you have to be careful about watering. If you dwell in the redwood forest, your options are far fewer because so little of the suns energy reaches the forest floor.
Shade gardening is a challenge for several reasons. The forest canopy limits the light available to the plants below and many trees drop leaves that exude toxins during the process of decay. One such toxin is tannin, which is found in the leaves and bark of many trees and acts as an inhibitor to the growth of young plants.
Another problem lies in the inability of young plants to compete with tree roots that suck water and nutrients from the soil. Some trees also have allelopathic tendencies, meaning that the tree or plant exudes chemicals from its roots or leaves that inhibit the growth of other plants. .
Our own native Monterey Cypress, for example, is extremely allelopathic. It has been my experience that there are practically no plants that will survive more than a couple of years within the root zone of a cypress. Furthermore, being a coastal tree that relies primarily on fog for its moisture, the Cypress creates a dense mat of tiny roots just under the soil surface that suck every bit of water available. Even after weeks of soaking rain, if one digs 6 inches down into the soil under a tree, they will frequently find that the ground is bone dry.
There are certain measures to be take to alleviate some of these problems. Cleaning up fallen leaves will prevent them from smothering young plants. The best tool for this is a small rake that can be maneuvered between plants, or perhaps (if you can bear it) a leaf blower. Keeping your trees pruned will allow more light to reach your garden as well as reducing the quantity of leaf fall. Planting in raised mounds will enable your plants to develop roots without having to compete with the roots of existing trees, although after a period of time you can probably expect that the tree will expand its root system too.
In rural forested areas one also has to consider other forest dwellers that will view your garden as a supplement to their diet. One deer can make quick work of all your plants, so it is usually advisable to stick with natives that they find less appetizing. The plants mentioned below which are natives can be assumed to be more deer resistant.
Though many plant species enjoy a partial shade environment, those that will thrive in the deep shade are far fewer. Oak woodland areas often provide dappled sunlight, whereas the redwood forest is primarily deep shade
Native to this area Wild ginger (asarum) makes for a nice verdant green groundcover, but it requires moist soil to thrive. As with many other forest natives it is summer-dormant, meaning that unless irrigated it will die back in the summer unless irrigated.
Five fingered maidenhair fern (adiantum aleuticum), another native to our locale, can reach up to three feet in height and will also go dormant if not irrigated.
Giant Chain Fern (woodwardia fimbriata) can grow to nine feet and makes for an excellent backdrop to your shade garden. Though it is not usually considered to be drought tolerant, once well established it will survive with very little supplemental water in the deep shade.This plant should be given plenty of room as it can get enormous.
Bleeding Heart (dicentra Formosa) is one of those rare gems of the forest that have a particularly showy flower and thrives in deep shade. It spreads along the ground wherever there is moisture and grows about one foot high. Once established , it is easy to dig up a section to transplant. I have seen an entire hillside in Bonny doon covered with bleeding hearts, though it will die back in the summer.
Alum Root (heuchara micrantha) can be found in our mountains, usually growing along the edge of stream or seep. It has a large green leaf and sends up multiple stalks bearing white flowers. If you want a variety of different colored leaves and flowers, heuchara has numerous cultivars. Most often called Coral Bells, these cultivars are valued primarily for their splendidly colored foliage, ranging from purple to lime green, as well as several variegated varieties.
Other good bets for the shade garden
Bears Breech (acanthus mollis) I have had a good deal of success growing acanthus under the redwood canopy. Even in deep shade areas, this plant produces a showy flower stalk and has large lush shiny leaves. Moderately deer resistant, it will survive without water though the leaves will wilt and shrivel. This is another plant that gets fairly large, and will spread throughout your garden. It is most prudently used as a backdrop, kept well away from other plants. Once established, it can be very difficult to eradicate.
Oregon Grape (Mahonia Aquafolium) I have only of late gained an appreciation for this plant. While the foliage is a bit holly-like (shiny with little spiky leaves) for my taste, it more than compensates with its bright yellow flowers that turn to clusters of purple fruit. Valued medicinally as an antioxidant and antibacterial, it is also evergreen and is tolerant to drought and cold.
Dead Nettle (Lamium) Though its name doesn’t sound very attractive, there are some cultivars that will do wonders to brighten up areas of deep shade. Primarily a low growing groundcover, it comes in several colors, including in almost luminescent silver. The flowers range from purple to yellow and it will spread wherever it finds water, creating a shimmering carpet. Very deer resistant, but it needs regular irrigation.
Hellebore (helleborus) This plant seems to thrive in many conditions where others falter. It can take deep shade to full sun, is tolerant of salt air along the coast, and even seems resistant to allelopathic roots (one of the very few plants that will grow under cypress). The hellebore has several cultivars which vary in height from one to three feet and bears striking hanging clusters of lantern-like flowers which range in color from creamy white, to yellow and purple.