By Brent McGhie, Butte County Master Gardener, August 22, 2014
These stately trees provide Californians with iconic vistas and are prized for the shade and beauty they give landowners. Oaks also furnish wildlife with food and shelter and, not incidentally, increase property values. By keeping a few cultural practice guidelines in mind, landowners can become good stewards of their oaks and preserve these trees for generations to come.
The key to living with oaks is to disturb them as little as possible. This is especially true of the root crown (the base of the trunk) and the root zone. The root zone of an oak tree covers an area one-third again larger than the outermost edge of the tree's foliage. Strive to keep this area as natural as possible.
The fungal disease “oak root rot” (Armillaria mellea) has evolved with California oaks. It is parasitic on oaks and other plant species, but if oaks are growing naturally in our moist winter/dry summer environment, this fungus is kept in check. However, if oaks are provided with summer irrigation in their root zone, Armillaria can become an aggressive, deadly pathogen. Do not water any plants under oaks during the summer: if they need watering, they do not belong there. Instead, native plants that are adapted to our Mediterranean climate can be grown under oaks. If winter rains are unusually low, a supplemental watering can be provided in the early spring. Do this by watering deeply in the outer two-thirds of the root zone.
Mature oaks do not normally require pruning, exceptfor the removal of dead, weakened, diseased, or dangerous branches. However, to incorporate oaks into a fire-resistant landscape, branches should be pruned away from the ground and kept from touching or hanging over buildings. Additionally, if the landowner wishes, an arborist can be contracted to thin 10-20 percent of the leaf area from branches three to six inches in diameter. Such thinning allows increased light into the tree canopy and decreases branch weight and wind resistance. Light pruning can be done any time of the year, but heavy pruning should be accomplished during the winter dormant season for deciduous oaks and in July or August for the evergreen interior live oak.
Under natural conditions, decomposing leaf litter provides oaks with an adequate supply of recycled nutrients, so oaks do not
normally require fertilizing. If the leaves beneath an oak have been raked up, supplemental feeding is appropriate. If they do require fertilizing, nitrogen is the element most heavily used by oaks; it should be applied at the rate of two to four pounds of actual nitrogen per thousand square feet of area. Either nitrate or organic fertilizers can be used, but organic fertilizers are preferable because their nutrients are released more slowly and they improve soil structure as well.
By Cindy Weiner, Butte County Master Gardener, September 5, 2014
Native bulbs prefer good drainage, although most will tolerate quite a bit of clay. You can improve drainage by planting on a slope or by mixing in a few inches of coarse sand in the bottom of the planting hole. Native bulbs are quite small compared to daffodils; they are usually less than an inch in diameter, but planted 2 to 4 inches deep. No amendments are necessary. If gophers are present, you will need to protect the bulbs. Plant in October or November after the first rains and be prepared to irrigate if the rains fail. Native bulbs can be planted in a mixed border with annuals and perennials that get little summer water or in other places that aren't irrigated routinely. The plants can be irrigated until the flowers start to fade. Once dormant, the bulbs will rot with too much irrigation. Allow the leaves to dry out completely before removing them as they are producing food to store for the following year's growth and bloom. Most bulbs prefer sunny locations, but some, like fawn lilies (Erythronium), globe lilies (Calochortus) and true lilies (Lilium) do better in filtered shade.
By Eve Werner, Butte County Master Gardener, September 19, 2014
In recent decades, hedgerows have largely been replaced in California by mown, cultivated, or weedy edges as farmers seek to maximize their productive acreage. But hedgerows are coming back into favor as scientists document the many benefits that they offer to farmers and the environment. Consider the following:
- Hedgerows can perform several distinct functions. Depending on the plants selected, they can provide wildlife habitat, dust control, wind breaks, biofiltration, pest control, crop pollination, and natural beauty.
- California native plants make effective hedgerows. The natives bloom and set seed later than weedy invasive plants. The timing of their blooming and seeding is just right for many beneficial pollinators and too late for many pests.
- Hedgerows can help control insect pests. UC studies have shown that hedgerows have 90% fewer crop pests and 60% more beneficial parasitoid wasps (tiny, non-stinging wasps that prey on stinkbugs, aphids, scale, and many other harmful pests) than conventionally managed edges. Croplands adjacent to hedgerows have 10% more parasitoid wasps than conventionally-edged fields.
- Hedgerows support insectivorous birds that eat the larvae of the coddling moth.
- Populations of potentially harmful animals (such as field mice and gophers) are present in equal or lesser numbers in hedgerows than in conventionally-managed edges.
- Populations of predatory animals (such as raptors) that prey on potentially harmful animals are much higher in hedgerows.
- Hedgerows support native bees by providing undisturbed habitat, pollen, and nectar. Some species of native bees, such as Mason bees, are individually more effective at pollinating flowers than are honey bees.
While the benefits of hedgerows to farmers are apparent, the hedgerow concept can be of use to homeowners, too. A smaller hedgerow, planted along a property boundary, will attract pollinators, pest predators and birds to your yard. Landscape-friendly California native plants that are suitable for a suburban yard and providing habitat, shelter, pollen, and nectar include California Redbud; Ceanothus; Buckwheat; Coffeeberry; Manzanita; Coyotebrush; Deergrass; California Fuchsia; Milkweed; Cleveland and White Sage; Yarrow; and Penstemon.
If you are looking for a way to screen views or define the edges of your property, consider planting a mini hedgerow!
By Brent McGhie, Butte County Master Gardener, October 3, 2014
Oak root fungus attacks the sapwood just beneath the bark of the lower trunk and roots of infected plants. This disrupts the flow of water and nutrients in the plant. When this occurs, the first above ground symptoms to be noticed are stunted shoots, discolored leaves and excessive leaf drop. There may also be cankers and gumming of the trunk just below or at ground level. When the bark of infected roots or the trunk beneath the soil line is peeled away, cream-colored fungal threads (mycelia) are present. These mycelia have a distinct mushroom-like odor. They may appear on the surface of herbaceous plants as well. Honey-colored Armillariamushrooms typically emerge anytime between Thanksgiving and Valentine's Day and, when present, are always found in clusters around infected plants.
Armillaria is always associated with wood; it does not live independently in the soil. Armillaria spreads from plant to plant when a root from an uninfected plant grows into the fungal mycelium, or when specialized fungal structures called rhizomorphs bridge a short distance (less than one inch) between a diseased root and an adjacent healthy plant's root. Once Armillaria comes in contact with a living root, it dissolves the bark and decays the wood. Although the interaction of environmental factors is not completely understood, it appears that high soil moisture, high concentrations of Armillaria, and close plant spacing are key factors that favor the spread of oak root fungus.
There are no fungicides available that kill Armillaria. The only effective controls are planting resistant plant species and employing other appropriate cultural practices such as avoiding over-irrigation and avoiding moving infected root pieces to new uninfected locations. Drying Armillaria kills it. Reports state that oak root fungus growth has been slowed or stopped by removing the soil from around the base of an infected plant and allowing the area to dry completely. If an area is suspected of being infected with Armillaria, prepare the soil by removing roots and wood debris and air-drying the soil before planting. Then provide the new plants with adequate drainage and appropriate irrigation. Do not over-water.
By Cindy Weiner, Butte County Master Gardener, October 17, 2014
By fall most summer-blooming plants have run their course, while summer-dormant plants are just beginning to start their new growth for the season. You may feel your garden needs more color. Luckily for the gardener, there are some native plants which continue to bloom well into the fall and others which begin to bloom in late fall.
Native to many plant communities throughout California, including Butte County, California fuchsia (Epilobium canum) is a powerhouse that deserves a spot in every garden. This spreading perennial in the evening primrose family is available in low-growing forms that reach around six inches and upright varieties that can get up to three feet tall. The narrow leaves of the California fuchsia can be green, gray-green or gray and its trumpet- shaped scarlet flowers are very attractive to hummingbirds and butterflies. It blooms from early summer until the weather turns cold, requires little water and grows in full sun. Its branches should be cut back in late fall after flowering is finished.
Chaparral currant (Ribes malvaceum) is a shrub of the gooseberry and currant family native to foothills in the Coast Range. In the wild it can grow in full sun but may do better with part shade in our area. It grows to five feet tall with an upright form. Its dull green leaves are hairy and lobed and are deer-resistant. In the wild it is summer dormant and will lose its leaves. Once established, it requires no summer irrigation but will stay green longer with some supplemental spring watering. It begins growing again in the fall and will bloom from around October until March. Chaparral currant has pink flowers growing in drooping clusters two to six inches long. The flowers are a good source of nectar for resident hummingbirds when few other plants are in bloom. Its blue-black fruit attracts many other birds. Because it requires little supplemental water, it can be planted under native oaks. It requires little pruning.
Fall is the best time to plant natives as they have time to get their roots established before the heat of next summer. If you plant some fall-bloomers now, you'll have some great color at this time next year.