Use caution when planting near oak trees in California.
We were recently hired to design a landscape in an area that was covered in oak trees. To do this took a bit of research because planting near oaks can be tricky. Read on to learn what to do, and what not to do, when planting around oak trees.
The biggest concern when planting around oaks is to be careful not to disturb the trees’ root systems. This is especially crucial for mature oaks, who have lost their youthful ability to tolerate change and recover. It is important to not plant in the oak tree’s root protection zone, which extends beyond the tree’s drip line as shown below.
The first part of an oak tree’s root system to develop is the taproot, which will go deep into the earth looking for a water source. Next, the lateral roots begin to form and spread as far as 90 feet from the trees base and are shallow, staying as close as 18 inches from the soil’s surface. This horizontal root system is what will support the tree for the extent of its life. This is why we must be very careful when planting around oak trees so as not to disturb the tree’s shallow roots. Plant at least 6 ft from the tree’s drip line and only use hand tools, no heavy machinery. If you’re digging and find a root, stop digging there, and find another place to plant. It’s a good idea to plant immature plants that don’t require digging a deep hole.
The Californian Mediterranean climate has long, dry summers, so native plants have needed to adapt in order to survive in this climate. Much of the native vegetation, including oak trees, have sclerphyllous foliage, meaning that their leaves are small, dark, and have a waxy outer layer to retain moisture in the dry summer months. Only during times of extreme drought will an oak tree need to be irrigated and it is best to get the advice of an Arborist if you think your oak does need water.
Watering your oak trees can cause fungi such as Armillaria mellea or Ganoderma lucidum which will produce root rot, and can ultimately lead to the tree dying. Signs of root rot include:
–Small, yellowing leaves
–Wilting or dying branches
–Seeing fungal growth around the base of the tree or on the bark,
–Smelling a mushroom like odor.
If your trees exhibit any of these signs, call an Arborist and have them to come and treat your tree’s root rot.
As you can observe in nature, there are many beautiful species of plants that thrive in an oak woodland. When choosing plants to adorn your oaks, it is best to mimic the wisdom of nature. Choose only California native, drought-tolerant plants that grow naturally under oak trees. Las Pilitas nursery in Santa Margarita has a fantastic website with helpful advice on choosing native plants, and specifically planting under oak trees. Because a newly planted garden will need water to establish root systems, plant in the fall or winter when the plants can be naturally watered by rainfall and during the time of year when oaks are used to getting water. Avoid planting anything after the rainy season as adding water near your oaks during this time can cause root rot.
For the design that I made, I chose to plant Heuchera maxima, Salvia spathacea, Ribes viburnifolium, Ribes sanguineum glutinosum, Holodiscus discolor, and Arctostaphylos densiflora ‘Harmony’. These plants all do well in shade, under oaks, and require no irrigation in the summer. This is a truly drought-tolerant, low-maintenance garden. I love taking a page out of mother nature’s design book, and installing a completely California native garden that needs no fertilizer, irrigation, or pruning – purely natural and beautiful! Stay posted for pictures once the garden is installed.
As you can see, planting near oaks can be risky because of their shallow root system and susceptibility to root rot. Be careful when planting around your oaks and be sure to get the advice of a professional if you need it.