When customers invite an arborist on to their property to discuss the state of their trees, they are opening themselves up to a critique of their arboreal landscape. A common question we often receive during these appointments is our opinion on landscaping under oak trees.
In the Midwest, oak trees are often the specimen trees on our customers’ properties. These anchor trees are generally where the focus of their attention lies. We often assess the understory of a high value tree, and pending on the mix of shrubs, plants or grass, ideas to improve the aesthetic and health will be bandied about.
If you have a beloved oak tree in your yard, you may be questioning whether you should plant under it and if doing so will impact the health of the tree. Here are some things to consider when starting the process of planting under oak trees.
How Much Sun Is Available?
Planning any new garden generally starts with the same question: “How much sun do I have underneath my oak tree?” Knowing how much sun is going to stream through your canopy will determine the plant mix that will work when planting under your oak tree.
Take into consideration the height of the branches under the tree. Are they particularly low? Will they cast deep shade or exclude low angled light in early and late summer? Deep shade requires low light planting choices.
Or is the first branch in the canopy dozens of feet from the ground? This means sunlight is more diffused and able to penetrate to the ground. In this area you can plant partial sun loving plants.
Are there other plants or structures blocking the sun? If your neighbor’s garage or house is directly to the south of your proposed garden, or if there is another large tree adjacent to your planting bed, you will need to plan on planting shade tolerant plants.
Assess the Planting Area
The amount of work that will go into preparing for planting under oak trees depends on the current state of the area. If the space under your oak tree has a layer of duffy leaves or woodchips with no plant competition, then you are one huge step ahead in the process. If the area is already covered in shrubs or small trees, or the spot is a dense patch of grass, things can get more time consuming.
Remove Invasive Plants
Part of the inspiration for planting under an oak tree might be the removal of invasive plants currently residing under the shade of the tree. Buckthorn, honeysuckle and garlic mustard are three of the many invasive plants that bedevil disturbed areas in our yards and natural areas. They have a tendency to smother adjacent plants and create impenetrable shade in which no other plants can grow.
Getting rid of all three can be a time-consuming task, but once you do, you’ll unveil a blank canvas on which to plant.
Removal of garlic mustard is generally a war of attrition. It pulls easily but requires patience and perseverance to stay on top of future seedlings that sprout from a bank of seeds cached in the soil. Garlic mustard is biennial, which means it flowers in the second year, so second year plants are doubly important to pull on account of their prolific seed production after flowering. It is recommended that flowering plants are bagged and thrown out with your trash versus composting because pulled plants can still set and drop seed!
Honeysuckle and buckthorn provide their own challenges when weeding out of a new planting area. Pulling shrubs can be an arduous task and require the proper tools. Honeysuckle is the more forgiving of the two plants on account of shrub form and shallow root system.
Eco Tree will use a weed wrench when pulling smaller trees and shrubs, thus minimizing the root disturbance under the canopy of your oak tree. A shovel can be used to lever some root systems out of the ground, but special care must be given to avoid damaging surface roots.
Buckthorn is more of a small tree than a shrub. If allowed to grow it can reach the size of a decent sized apple tree and a chainsaw would then be your only hope. Once removed, buckthorn is more than happy to resprout from the remaining stump, so chemical treatment to kill the stump is the easiest option.
If the buckthorn stump lies on the edges of the oak tree’s drip line and a good distance from the trunk, a stump grinder can also be used to remove it and prevent resprouting. Again, minimizing root damage with heavy equipment and tools requires a deliberate and delicate process.
Removing Grass for Planting Under Oak Trees
If there is grass around the oak tree you wish to plant under, you have a couple different approaches to take. Smothering your lawn with multiple layers of newspaper or cardboard can be an easy method of eliminating lawn. The biggest benefit of this technique is the fact that you will not disturb the soil horizons by digging. The downside of smothering lawn is the time it takes to kill the grass and get it to break down. Ideally, the planting bed under your oak tree will remain covered for an entire growing season.
When smothering the lawn, always wet the paper or cardboard to help improve the decomposition of the material. Avoid placing the paper near the trunk flare, so as to allow some rainwater to enter the soil as stemflow. The goal of smothering with wet paper and cardboard is to kill the grass in a growing season and will not serve as a permanent weed barrier because it will eventually break down.
If the lawn under your oak tree is healthy and thick you may consider using a sod stripper. A sod stripper will cut the soil about two inches below the surface of the lawn and remove most of the grass rhizomes to prevent resprouting. If your sod stripper cuts clean strips you will be able to roll the grass up and either compost or reuse the grass strips in another part of your lawn.
One option is to flip the sod strips grass side down and outline the garden bed around your tree. This will provide a natural edge that will slowly breakdown and help keep the mulch contained in your planting bed.
When planting under oak trees, proper bed prep is key to a successful garden and a healthy tree. Clearing the planting bed under your oak will facilitate maintenance of your new garden bed. Consider spreading a layer of mulch to define the area you laid out and help protect the recently exposed soil to drying, erosion and potential sprouting of weeds. Depending on how quickly you take on the next phase, which is planting, having a mulched bed will give your new planting area an organized and established look.