Recently  I visited the home of  a fellow Master Gardener who lives near Napa's eastern hills off  Third Avenue. She has majestic native oaks in front of her home, and I asked her how old those trees might be. She said maybe 200 years.

Napa Valley and Napa County have many wonderful old oaks of various varieties. These old oaks add so much to our lives. Some retain their leaves all year round and others lose their leaves each fall. As the ones that retain their leaves grow, the older leaves fall and create a carpet of dried leaves. I don't rake these up but leave them to decay as nature intended.

The trees' huge root systems hold the soil and keep it from washing off steep hills during storms. The trees provide acorns for birds, squirrels and other wild creatures that share the land with us.

Native Americans would roast acorns and grind the interior into flour for use in cooking. At Indian Grinding Rock State Park near Jackson, California, you can see over a thousand grinding holes used by Native people. It is well worth a visit.

The leaf litter under the trees adds to the health of our soil. When you walk on this litter it is rather like walking on a damp sponge. The litter retains water for use by the massive root system, which allows it to trickle down to our aquifers.

Napa County has nine native species of oak. The oak genus (Quercus) is native to the Northern Hemisphere, but oaks are found all over the world. Oaks adapt to their climate. All of them produce acorns; however, the size and shape of the acorns can vary. I found some last winter that were huge. They did not come from my trees so wind or birds must have brought them.

Often as I work around my garden, I find that squirrels or birds have planted acorns. They probably intend to return and eat them but have forgotten where they planted them. So, I have a variety of oaks coming up in odd places.

Since I don't want to live in an oak forest and already have several large oaks, I pull up these seedlings. The top may be only a few inches tall, but the tap root  can be a foot long or more. After an oak tree starts to grow well, it sends out feeder roots that may eventually extend beyond the oak canopy.

Oak roots form a bond with other soil residents, a synergistic relationship known as a mycorrhizal network. This network is held together by mycelium on the roots. Some researchers believe that trees “talk” to each other through these networks, sharing resources and other information. Fungi and mushrooms underground play a big role in this process. If you would like to learn more about how trees talk to each other, visit this web site: https://www.nationalforests.org/blog/underground-mycorrhizal-network.

Oaks are watered by winter rains but do not need water during summer. They have adapted to this annual wet-dry cycle.

Keep plant material away from the base of the trunk to minimize diseases that might kill the tree. Also avoid planting under oaks, which can alter the soil makeup.

Coast live oaks are native to Napa Valley and thrive in most of Napa County. Valley oaks like flat areas and a high-water table. Black oaks and blue oaks prefer hillsides with drier soils. These are the oak species that keep our hillsides in place. They played a big role this past winter in preventing mudslides.

Many mature oaks can reach 70 feet in height. When choosing a place to plant an oak, make sure you have room for this type of growth. As the trees grow, the shade under them becomes denser.

Except for one tree in my yard, the other 20 were planted by birds or by us. They have grown over the years to be wonderful trees, reflecting the uniqueness of Napa Valley.

Workshop: Join UC Master Gardeners of Napa County for a workshop on “Low Water Plants” on Saturday, June 24, from 10 am to noon, at Las Flores Learning Garden, 4300 Linda Vista Avenue, Napa. Find details and reservation link at https://ucanr.edu/2023LFLGLowWater.

Library Talk: Join UC Master Gardeners of Napa County on Thursday, July 6, from 7 pm to 8 pm, for a Napa Library talk on “What's Bugging You: Insects and Pests in the Garden,” via Zoom. Register to get the Zoom link: https://ucanr.edu/2023Jul6LibraryTalk 

Food Growing Forum: Join UC Master Gardeners of Napa County for a forum on “Beverages from Your Garden” on Sunday, July 9, from 3 pm to 5 pm, at University of California Cooperative Extension office,  1710 Soscol Avenue, Napa. Register here:
https://ucanr.edu/2023FoodForumJul 

Library Talk: Join UC Master Gardeners of Napa County for a talk on “Resilient Landscaping for Drought and Fire” on Tuesday, July 11, from 4:30 pm to 5:30 pm at St. Helena Library, 1492 Library Lane, St. Helena. Register here: https://ucanr.edu/2023StHelenaLibraryReslientLandscapeJul 

Help Desk: The Master Gardener Help Desk is available to answer your garden questions on Mondays and Fridays from 10 a.m. until 1 p.m at the University of California Cooperative Extension Office, 1710 Soscol Avenue, Suite 4, Napa. Or send your questions to mastergardeners@countyofnapa.org. Include your name, address, phone number and a brief description of the problem. For the best results, attach a photo of the plant. You may also leave a voicemail message with the same information at 707-253-4143.