One of the more frequent questions I get in my capacity as local plant nerd is what can I plant underneath my oak trees.
Planting under oaks is tricky for a number of reasons. First, they are large and evergreen, thus allowing precious little sunlight to reach the ground anywhere near the trunk. Secondly, oak leaves have tannins, which do a good job preventing anything from growing successfully underneath. Finally, oaks hate regular summer water, and it’s difficult to plant anything and not water for six months. Oaks have relatively shallow root systems and the more you disturb and water the higher your risk of damaging the tree.
My solutions are threefold:
Don’t plant anything within 5 feet of the trunk of your oak
Find tougher species that can handle the dappled sunlight and harsh tannins
Plant in October, so you can get 6 months of water to your new plants without risking damage to your tree.
Now to the species I enjoy, from small to large. Not all are local natives, but all are relatively easy to find at Theodore Payne or Santa Barbara Botanical Garden:
Heuchera, or coral bells. Come in a million different colors. My favorite part is you can divide these each year to make new ones.
Yerba buena forms a slowly spreading carpet with darling little white flowers. Some medicinal uses for you backyard pharmacists.
Hummingbird sage. Well, duh. Also great for divisions.
Juncus is my favorite grass for under oaks. In my yard I have them mixed in with:
Dudleya hassei, I have to admit this was Antonio from Nopalito’s idea. It’s a great color combo and they need little to no water. I’ve also done divisions of these this year.
Monkeyflower also comes in a million colors. They may look a bit scraggly in August (what doesn’t) but they are staples for under oaks, lasting 4-8 years.
Barberries are my new favorite. Also known as Mahonias. Repens and Compacta are both slowly spreading and forming low cover for all the birds and lizards in my yard. Berries are edible for humans as well.
Snowberry isn’t remotely fancy, but dependable, spreading and fruiting. Dormant for a few months in the winter.
Nightshade goes a bit dormant late summer but it’s a reliable spreader and provides some nice under-oak purple to the palette.
Ribes has numerous species that I like to use in my yard. For low growing nothing beats Catalina perfume, which stays evergreen unlike its cousin species. For mid sized I prefer the gooseberry:
Now we start to get a bit larger, 5-7 feet:
Carpinteria californica, or bush anenome. Blooming right now in my yard. They will do better with more water but are fine with just occasional in the summer.
If you are like me you need to have at least one manzanita per 20 square feet. Howard McMinn to the rescue, he doesn’t mind a long waterless summer as much as most.
And if ceanothus is your obsession I have had tremendous success with my favorite lady Joyce Coulter (sorry this belongs with the ground covers, she’s a creeper)
I have never had great success with coffeeberry. But they come in a number of varieties and are lush and will bear fruit if you are patient (both literally and metaphorically)
Toyon is about as big as I’d want to plant under an oak. They don’t grow quickly, and you won’t see fruit for about a decade but they can do well once established.
Well I hope that gave you plenty of ideas… Please comment if you think there’s something I missed.