What’s the best oak for my garden?

Question: I want to plant another oak tree at our home, which is on 2 acres, but I've heard about sudden oak death. What kind of oak should I plant, and what plants would thrive around my oak trees? Also, how much do I need to water the oak seedling and my other mature oak trees?

Answer: Since it first appeared in the mid-1990s, sudden oak death has killed hundreds of thousands of native oak and tan oak trees in California. Trees in the red oak group are susceptible to the disease, but so far, oaks in the white oak group have not been affected by sudden oak death.

Valley oak, Quercus lobata, is a good white oak to plant in valley bottoms with fertile soil, less than 1,000 feet above sea level and away from salt water. The valley oak grows to be a very large tree; make sure to give it plenty of room to grow. Oregon white oak, Quercus garryana, is another good choice that grows in many habitats below 7,000 feet of elevation. It’s a smaller tree than valley oak and tolerates crowding somewhat better. Finally, blue oak, Quercus douglasii, grows in poor, rocky soil and in hot, dry foothills, from 500 to 2,000 feet of elevation.

All white oaks, especially blue oaks, are susceptible to powdery mildew. For this reason, it’s best to plant them at least a mile from the ocean.

When planting young oaks, be sure to give them enough water. Remove nearby weeds that compete for water and apply mulch at least 1 or 2 feet from the tree, to help retain soil moisture. Make sure the mulch does not touch the trunk. Water the seedlings near the tree base, but as the tree grows, apply water away from the base, at the drip line.

Transplant young trees in the fall or winter to take advantage of winter rains. For the first year, water the seedlings a little every day during hot, dry conditions until the oak trunk is at least an inch in diameter. You can taper off watering as the tree becomes established.

All oaks native to the North Bay prefer to get water in the winter and spring, when soil temperatures are cool. However, if the soil is dry in the spring and there’s little chance of rain in the forecast, you can give your oaks additional water.

One good way to do this is to place a soaker hose just inside the tree’s drip line, cover the hose with mulch and let the water run until the top 12 inches of soil are moist. This may take from 20 minutes to a few hours, depending upon the soil.

If your tree is on a steep slope, start a timer as soon as you start watering. Let the water run until you begin to see runoff, then turn off the water and note how much time has elapsed. Wait at least an hour, then turn on the water again and let it run for a minute less than the first time. Turn the water off before you see runoff.

Mature oaks are adapted to dry, hot summer conditions. They usually do not tolerate routine summer irrigation, which can encourage the growth of fungus that attacks the roots and crown of an oak. However, during prolonged periods of drought such as now, even mature oaks can benefit from infrequent watering, maybe once a month or so, depending on your soil. Deeply soak the outer two-thirds of the area in the root zone under the tree, 6 feet away from the trunk and to the edge of the tree’s drip line.

When landscaping around mature oaks, it’s best to plant landscaping at least 10 feet away from the tree’s canopy. Do not plant water-hungry plants at or within the drip line of native oaks. Try planting California native plants that are adapted to living beneath oaks, such as ceanothus, monkey flower, baby blue eyes or California poppies. Many native plants are also colorful, attractive and pest-resistant. Native grasses, like California fescue and blue gamma grass, are becoming increasingly popular, grow naturally under oaks and require little water and maintenance.

For more information on planting oaks and selecting compatible plants, see “Living Among the Oaks: A Management Guide for Woodland Owners and Managers,” at bit.ly/3g6eIUj. Sudden Oak Death: bit.ly/35fh6Cg

It’s time to plant garlic! Most local nurseries carry a variety of garlic bulbs grown specifically for home gardens.

To plant garlic, separate each clove from the bulb and plant pointy side up, 4 to 6 inches apart and 2 to 3 inches deep. While you’re at the nursery, pick up some late-winter- and early-spring-blooming bulbs like daffodils and tulips.

It’s not too late to plant a few more cool-weather veggies, such as bok choy, peas, radishes and salad greens. One you may not know, mache, also known as “corn salad,” is a mild-tasting salad green that will overwinter in your garden. It also can be cooked like spinach and used in soups.

Did you lose some plants to the drought? Consider replacing them with California native plants. This is a good time to plant native shrubs, trees and flowers. They are well-adapted to our climate and soil, use less water and promote wildlife biodiversity in your garden.

If you have deciduous trees, consider composting the leaves. You can run a lawn mower over them to break them down and encourage decomposition.

Use the municipal green waste bin to dispose of diseased plants or seed-bearing weeds. High temperatures are required to kill weed seeds and pathogens; commercial compost piles can heat up to 190 degrees. If you live in Sonoma County, do not put poison oak, yucca tree trimmings, bamboo, cactus nor palm fronds in the green bin. Instead, throw them into the regular landfill trash can.

Contributors to this week’s column were April Lynch; Steven Swain, UCCE environmental horticulture adviser, Sonoma and Marin counties; Laura Eakin; Karen Felker; Laura Southworth; and Debbie Westrick. Send your gardening questions to scmgpd@gmail.com. The UC Master Gardener Program of Sonoma County (sonomamg.ucanr.edu) provides environmentally sustainable, science-based horticultural information to Sonoma County home gardeners. The Master Gardeners will answer in the newspaper only questions selected for this column. Other questions may be directed to their Information Desk: 707-565-2608 or mgsonoma@ ucanr.edu.