Plant List and Procedures
Lichter, J. and Ellen Zagory. HortScript 11, March, 1995
The Oak Habitat, Growth Habits and Roots
California native oaks have evolved under the cool, wet winters and hot,dry summers typical of our Mediterranean climate. Through adaptations such as the development of deep and extensive root systems, various water conserving leaf characteristics, and a slowing of growth in the summer, these trees are able to survive the prolonged seasonal droughts which typify the Central Valley. California native oaks often produce sinker roots within several feet of the trunk, which grow deep into the soil profile, providing the oak access to water as the summer progresses. Lateral roots are commonly shallow and extend well beyond the drip line of the tree. Maintaining the health of the oak root system is the key to successful landscaping around oaks.
Tree root health is largely affected by mechanical injury, physical and chemical properties of soil, and pathogens. During landscape installation,oak roots may be directly injured by backhoes, trenchers, tillage equipment or shovels, or indirectly by altering physical soil properties due to grading and compaction. Frequent irrigation and compaction limit oxygen access to oak roots that favor pathogens, such as crown and root rot (Phytopthorasp.) and oak root fungus (Armillaria mellea). These fungi often lead to the decline or structural instability of California native oaks.
Recommendations for Landscape Planting, Establishment and Maintenance
As a general rule, strive to ensure that the environmental conditions both above and below ground are similar to those conditions under which the oak grows naturally. Therefore, an ideal landscape near most Central Valley oaks is one which will tolerate a minimum of maintenance and irrigation once established. An appropriate plant palette may be composed of plants native to the local region or those plants which will tolerate the local environment (California natives or other Mediterranean plants). When establishing landscapes near oaks, one should observe the following guidelines.
- Ensure that drainage from landscaped areas does not collect under oaks.
Saturated soils (especially near the tree trunk) when soil temperatures are moderate create ideal conditions for the establishment of crown and root rot and oak root fungus, which can kill trees. Ensure that landscape grading does not allow drainage to collect around the base of the trunk.French drains or other systems may be used to carry water away from the tree.
- Prevent tree injury and soil compaction during landscape installation.
Avoid traffic and storage of equipment in the oak root zone. Install irrigation lines at the soil surface and cover them with mulch. Dig planting pits by hand whenever possible to avoid root injury. Where equipment operation is essential in the oak root zone, install a 6″ thick layer of wood chip mulch to reduce soil compaction.
- Plant sparingly and away from the tree trunk.
Ideally, do not plant under the oak canopy or at least within ten feet of the mature tree trunk where buttress and sinker roots (critical to the health and structural stability of the tree) are located. The frequent irrigation required to establish landscape plants creates conditions favorable for the fungi that can infect roots. Plant sparingly. Dense plantings can compete with oak root systems for water and nutrients. Therefore, use plants as accents and specimens near oak trees.
- Irrigate landscape plants as infrequently as possible.
The main goal of the irrigation for newly planted plants should be to provide only as much water as required to establish them. The plants should be irrigated in as small an area as possible. A drip or micro sprinkler system can be used for this purpose. However, it should be operated in such a manner as to avoid saturated soils for long periods of time. Once the plants are established, they should be irrigated monthly, less often, or not at all during the summer.
- Plant appropriate species.
Select plants that tolerate the Central Valley climate, drought, the exposure to light as influenced by the tree, soils in the vicinity of the tree (pH, drainage, texture, etc.), and common pests. Many California native species or species from Mediterranean climates are most suitable for planting under oaks. Consider the ultimate size of the plants selected and whether or not they will interfere with the tree canopy, views or structures.
- Utilize an appropriate soil surface cover.
Avoid paving over the oak root system; the impermeability of these surfaces as well as the excavation and compaction associated with their installation damage tree roots. If an area in the root zone of a tree needs to be paved,limit the paving to as small an area as possible and either install pervious pavers or decomposed granite on grade with a minimum of compaction (no more than 80%) or utilize a deck with piers. In non-paved areas, a wood chip mulch is an ideal soil surface cover. Install the mulch by hand to avoid soil compaction.
A List of California Native Plants Suitable For Use Under Central Valley Oaks
How To Use This List:
Sketch the area to be planted, including the oak(s) trunk and drip line,other plants and structures. Indicate areas which receive full sun, partial shade, full shade or morning sun only. Choose plants from the list appropriate to the sun exposure in the area to be planted. Develop a planting design utilizing these species.
Full Sun (tolerates south and west exposure)
|Latin name||Common name||Comments|
|Adenostoma fasciculatum||chamise||A low growing form is available|
|Artemisia tridentata||basin sagebrush||Needs dead branches removed with age|
|Ceanothus ‘Concha’ and ‘Dark Star’||Dense, dark flowered varieties|
|Ceanothus cuneatus||buckbrush||White flowers|
|Ceanothus megacarpus bigpod||buckbrush||Tree type ceanothus which is one of the earliest to bloom|
|Dendromecon rigida ssp. harfordii||bush poppy||Showy, yellow flowers|
|Encelia californica||encelia||Showy, yellow, daisy-type flowers|
|Ephedra species||Mormon tea|
|Eriogonum arborescens||Santa Cruz Is. buckwheat|
|Fallugia paradoxa||Apache plum||Ornamental fruits|
|Forestiera neo–mexicana||desert olive||Blue fruits are ornamental|
|Fremontodendron species and cultivars||fremontia||Large shrubs with golden, saucer shaped flowers|
|Heteromeles arbutifolia||toyon||Showy red berries around Christmas time|
|Isomeris arborea||bladderpod||Yellow flowers year-round. Some object to the odor of the leaves|
|Lupinus albifrons||silver bush lupine||Short-lived but self seeds.|
|Mahonia nevinii||San Fernando barberry||Spiny leaves, good barrier plant|
|Pickeringia montana||chaparral pea||Purple flowers in spring.|
|Quercus durata||leather oak|
|Romneya coulteri||Matilija poppy||Large “fried egg” flowers, spreads by underground runners|
|Salvia leucophylla||coastal white sage||Summer dormant without irrigation|
|Aesculus californica||California buckeye||Summer dormant|
|Prunus lyonii||Santa Catalina cherry|
|Baccharis pilularis var. pilularis||dwarf coyote bush||“Pigeon Point” is the best cultivar for valley.|
|Eriogonum fasciculatum||California buckwheat|
|Salvia sonomensis||creeping sage||Short-lived, water monthly, needs good drainage|
|Zauschneria californica||California fuchsia||Many cultivars available, red, pink and white.|
|Zauschneria cana||island California fuchsia||Fine, silver-gray foliage|
|Achillea millefolium||yarrow||Mow after bloom to remove flower stalks.|
|Dudleya sp.||live-forever||Can be used as sparse ground cover, may freeze back in winters.|
|Keckiella cordifolia||heart-leaved penstemon||Summer dormant|
|Salvia ‘Dare’s Choice’||hybrid sage||Evergreen perennial with purple-blue flowers|
|Viguiera deltoidea ssp. parishii||desert sunflower||Killed to ground in cold winters|
Grasses and Accent Plants
|Agave deserti||desert century plant||Accent plant.|
|Nolina sp.||nolina||Accent plant.|
|Stipa pulchra||purple needle grass||Water monthly. Summer dormant|
|Yucca whipplei||yucca||Succulent-leaved accent plant|
|Clarkia sp.||Showy pink blooms, monthly watering, mow after seed set.|
|Eschscholzia californica||California poppy||Reseeds in disturbed areas, mow after seed set.|
|Lupinus sp.||lupine||Lupinus densiflorus and L. succulentus are reliableyear after year. Mow after seed set.|
|Nemophila sp.||baby blue eyes|
|Allium sp.||wild onion||Many sizes and colors/|
|Brodiaea sp.||Triteleia and Dichelostemma also. Summer dormant|
|Calochortus sp.||mariposa lily|
|Chlorogalum pomeridianum||soap plant||3-4 ft. flower spikes open in afternoon.|
Protect From Afternoon Sun (Partial shade)
|Latin Name||Common name||Comments|
|Arctostaphylos densiflora||Sonoma manzanita||Cultivars “Harmony”, “Howard McMinn” and “Sentinel”|
|Arctostaphylos rudis||shagbark manzanita|
|Carpenteria californica||bush anemone||Summer deciduous if irrigated|
|Ceanothus ‘Ray Hartman’||hybrid ceanothus|
|Cercocarpus betuloides ssp. blanclzeae||mountain mahogany|
|Comarostaphylos diversifolia||summer holly||Ornamental red fruits|
|Eriogonum umbellatum var. polyanthum||sulfur buckwheat||Useful as loose ground cover or subshrub|
|Garrya elliptica||coast silktassel||Ornamental “tassels” in winter|
|Garrya fremontii||Fremont silktassel||Ornamental “tassels” in winter|
|Mahonia pinnata||California holly grape||Monthly watering|
|Prunus ilicifolia||hollyleaf cherry|
|Rhamnus californica||California coffeeberry|
|Ribes malvaccum||chaparal currant||Summer dormant, winter flowering|
|Ribes speciosum||fuchsia-flowered gooseberry||Summer dormant|
|Rosa californica||wild rose||Invasive if irrigated|
|Symphoricarpos rivularis||common snowberry||White fruits on winter deciduous branches|
|Lyonothamnus floribundus var. asplenifolius||Catalina ironwood||Fern-like, divided leaves|
|Umbellularia californica||California bay laurel|
|Aristolochia californica||Dutchman’s pipe||Winter deciduous, water monthly|
|Vitis californica||California wild grape||Deciduous, auumn red color forms available|
|Vitis girdiana||Desert grape|
Grasses and Accent Plants
|Lymus glaucus||blue wild rye||Monthly watering|
|Muhlenbergia rigens||deergrass||A large grass up to 6′ tall. Monthly watering|
|Festuca californica||Califoria fescue||Monthly watering|
|Ceanothus ‘Joyce Coulter’||hybrid ceanothus||Medium blue flowers, good bloomers|
|Ceanothus maritimus||maritime ceanothus||Low shrub|
|Whipplea modesta||yerba de selva||Monthly watering|
|Dinlacus aurantiacus||sticky monkeyflowers||Pinch to encourage new, bushy growth. Water monthly|
Full Shade or Morning Sun
|Latin Name||Common Name||Comments|
|Ribes viburnifolium||evergreen currant||Best shrub for dry shade|
|Heuchera maxima||giant alum root|
|Monardella sp.||deer mint, pennyroyal|
|Salvia spathacea||hummingbird sage||Large maroon and red flowers, water monthly.|
|Sisyrinchium bellum||blue eyed grass||Summer dormant without summer water|
|Arctostaphylos pajaroensis||pajaro manzanita||Best manzanita for our area.|
|Mahonia aquifolium||Oregon grape||Monthly watering.|
Reprinted from Hort Script, No. 11, March 1995, U.C. Cooperative Extension.
prepared and edited by Richard B. Standiford and Pavel Svihra