Here in Northern California, we are blessed with many stoic and picturesque native oaks. Coastal Live Oak (Quercus agrifolia), Valley Oak (Quercus lobata), and Blue Oak (Quercus douglasii) are all found in this bioregion. Many people are talking about Sudden Oak Death and other oak ailments as a result of anthropogenic (man-made) influences. Fear not: By following some simple rules and planting specially adapted native plants, you can foster life under your oaks.
Our California oaks have evolved to have dry roots for the summer months. One of the main mistakes I see in consulting with homeowners and ranches is that irrigation is installed too close to the drip line of the oak. This “wet feet” easily can lead to rot and disease.
By choosing the right specialists for the very specific habitat of oak understory, you can achieve a full, vibrant understory that will bring hummingbirds and other wildlife right underneath the majestic oaks and into your window’s views.
The drip-line is where the edge of the branches make a circle that defines where the majority of rain drips out to the edge of the tree. In intact nature, you will see in the oak savannah where a diversity of plants are growing “at the skirt of the tree” due to the increased moisture of this drip-line perimeter.
These plants receive the benefits of more rain, running off the oak as well as more light than inside the canopy. This makes the drip line a sweet spot for many oak savannah natives.
Try these native plants on the drip line’s edge:
• Hummingbird Sage (Salvia spathacea)
• Sonoma Sage (Salvia sonomensis)
• Yarrow (Achillea millefolium)
• California Fescue (Festuca californica)
Likewise, if there is vacant space in the partial shade of the oak but also outside the drip line, then the list of edible plants below will do fine for you here in the Bay Area or locations with similar climate. As it is outside the drip line, it is safe to water twice per week.
• High Bush Blueberry (Vaccinium corymbosum) “Sunshine Blue” and “Jewel”• (Low Chill) Cherry (Prunus avium) “Royal Lee”
Note: Cherries like acid soil and in the low chill of the Bay Area, some shade can actually be a positive.
• (Low Chill) Apple: “Fuji” and “Pink Lady”
Note: Like Cherry, Apples don't mind light shade to trick them into thinking our winters are more pronounced than in full sun.
• Currants: Edible cultivars of currant do well in the light shade outside the canopy. As the food cultivars of Red Currant and White (ribes rubrum), White Currant and Black Currant (ribes nigrum) need more water than the native cousins, they need be separated for the benefit of the oak above. Under these perennial food crops, you can grow Rhubarb (Rheum rhabarbarum).
• Raspberry (rubus idaeus): Raspberry will tolerate the light shade.
Inside the drip line is another story. Inside the dark canopy of oaks is the realm of native plant oak specialists. These plants have adapted over eons to tolerate the shade of the oak as well as the intense acidity of the oak leaf duff. Additionally, these plants have taken growth habits that are vertically upright. This allows for them to stay above the leaf drop in autumn when the leaves can accumulate over a foot deep!
Note: Do your part and do not irrigate directly under your oak canopy, not near the trunk/root crown.
Try these native plants for within the oaks canopy:
• Iris (Iris douglasiana)
• Oregon Grape (Mahonia repens)
• California Barberry (Mahonia pinnata)
• Pink Flowering Curant (Ribes sangueneum)
• Golden Currant (Ribes Auereum)
• Fuschia-Flowered Gooseberry (Ribes Speciosum)
Note: All these native plants listed for under the oak canopy are drought-tolerant. To establish these plants, only water 1 time per week. Drip irrigation is the preferred delivery method, as it will target the new plants root zone without soaking the surface or overwatering. If the soil is workable, these plants can be planted in the wet season.
Joshua Burman Thayer is a landscape designer and permaculture consultant with Native Sun Gardens. He is the Urban Agriculture Supervisor for Tenderloin Neighborhood Development Corporation in San Francisco, Calif. Find him at Native Sun Gardens and read his other MOTHER EARTH NEWS posts here.
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