Many people have concerns about planting around oak trees and for good reason. Oaks do not tolerate summer irrigation, and those that insist on planting water thirsty plants like lawns near their oaks risk killing their trees by encouraging sudden oak death syndrome or other diseases. So that is why it’s especially important to select natives that are acclimated to this particular hydrozone. Once established, you can reduce or stop irrigation. As a tip, if you install your oak understory in the fall before the rains, you’ll have one season of “free irrigation” under your belt.
Coral Bells or Heuchera are an excellent choice for dry shade groundcover and will take your breath away when planted in large masses. There are many wonderful hybrids of Heuchera to try. For an easy growing choice, use Heuchera ‘Wendy’ with its green leaves, purple veining and tall flower spikes. This evergreen perennial can also be enjoyed in window boxes and will attract hummingbirds that you can watch from indoors.

If you want to entice hummingbirds into the garden, Hummingbird sage is another winner under oaks. Salvia spathacea spreads on its own to create a groundcover with bright pink flowers that bloom typically March through May.
Our Coastal Wood Fern, Dryoperteris arguta, is one of the few ferns that is both drought tolerant and evergreen. Since it can withstand root competition, it’s suitable for under trees like oak, bay and pine. To keep its lush, green appearance, simply remove older fronds as they brown.
Again since it can survive with little supplemental water, Pacific Coast Iris work wonderfully as an understory plant. Iris douglasiana with purple flowers or I. douglasiana ‘Canyon Snow’ with white flowers are sure to brighten any oak woodland.

Julie-
You are doing a great job with your newsletters – I always enjoy them. BTW. I’ve been hunting for Dryopteris arguta for at least 5 years, for under my own oaks and for use with clients because they are evergreen. Do you know of a source for them? No one I’ve been able to find is propagating them, perhaps because of a rumor a few years ago that they vector SOD.
If you know where to get some, please let me know!
You are right Claudia, this is one tough plant to find! I called my plant broker and even he was at a loss. I would try Yerba Buena in Woodside.
Does ‘Eleanor Roosevelt’ purple iris make a good understory (in shade) for a valley oak? Or does it need more (full) sun?
Hi Sean! I love Iris and have planted then under oaks in dappled sun (not full shade) and they have thrived. The only downside to these beauties is that their flower is somewhat short lived. But the Eleanor Roosevelt is a stunning purple…good luck!
how about bearded hybrid iris will it grow under my oak tree?
The natives are the best!
I live in Maryland and my azaleas are not doing well near my oak tree. Any ideas what would work well?
thank you,
Joan
I want a colorful flower under oak tree. What can I plant for low maintenance with lots of color
Hi Pat,
I guess it depends on how much sun you get under the oak and where you live. In the Peninsula area of SF Bay area if it’s 1/2 sun you can try: eriogonum, erigeron or epilobium (the native varieties). If you have mostly shade, you can try Heuchera- I like the natives here too but other hybrids should work.
I live in Redding CA area. I have an oak where it gets full sun. I need to find s plant that will tolerate the heat here. Do you have a suggestion?
Hi Debra. When in doubt, ask your local landscape designer or garden nursery professional. Here’s a garden center which I’m sure sells climate appropriate plants for oak understories.