How to Properly Mulch a Tree

Adding a ring of mulch around a tree is a timeless method of adding beauty to a natural feature in your yard. When done correctly, mulch around a tree adds a pleasing aesthetic by enhancing an area where it's difficult to grow anything, helps to lock in moisture around the roots, and as the mulch breaks down over time, it even provides vital nutrients to the tree. But when done improperly, mulch can kill the tree. Follow these simple steps to create a beautiful feature in your lawn without damaging the tree!

Step 1. Understand the 3-3-3 Rule

The first step is to decide how big you want your ring of mulch to be. A general rule of thumb is to remember the 3-3-3 principle: At least three feet in diameter from the trunk; at least 3" deep; and at least 3" away from the base of the trunk. We'll explain each of these steps in further detail below.

Step 2. Determine the Size of Your Mulch Ring

Using the 3-3-3 rule, you want the ring of mulch to be at least three feet in diameter. To determine this, measure four points from the base of the tree, at least 3 feet out from the trunk, and mark these four points. It's helpful to make your marks 90 degrees from each other, or make a mark at North, East, South, and West.

Step 3. Expose the Soil

Dig in! You want to remove all vegetation, so grass, weeds, and any other plants that are growing within your ring area. Make sure to get them all out to help prolong the time that weeds will grow through your mulch later.

We use a Garden Claw, like this one, to make this job MUCH easier. Break up the soil with the tool, then you can simply remove the vegetation by hand.

At this point you have a decision to make. Do you want the mulch to fall even on the lawn or do you want an edge so the mulch is held in place by a defined edge?

Determine the diameter of your mulch ring and begin exposing the soil.

Step 4. Create an Edge

There are many different ways to edge a mulch bed. The good news is that none of them are wrong! The bad news is, you have to decide what you want. Here's a simple breakdown to help you decide.

1. Live edge: With this edge, there is no defined edge. The mulch "spills" onto the lawn with very little definition between the edge of the mulch bed and the grass.

   1. Benefits: No edging to maintain and it looks very natural. This is a great edge if you are looking for the most natural look. Less digging and prep work to make the bed, as well.

   2. Cons: If you have a creeping grass, such as Saint Augustine, you will constantly battle the grass to keep it from spreading into your mulch bed. With most warm season grasses, it's best to have a more defined edge.

2. Defined Edge: Many options, including digging a simple ditch so the mulch rests against the soil under the grass; masonry or concrete edging, such as stone or brick; plastic, rubber, or metal edging that is either staked to the ground or installed in a shallow trench.

   1. Benefits: A well defined edge between the bed and grass that looks great when installed properly. Helps to keep grass and weeds from encroaching into your mulch. Holds the mulch in place and is easier to maintain the grass around it.

   2. Cons: Can be expensive depending on the material and the size of your bed. It is more labor intensive in that there is prep work and material to install. Will absolutely look terrible if not installed correctly. Does require maintenance to keep it looking nice, although some techniques and materials require less maintenance than others.

Now that you have chosen which edging you are going to use, go ahead and prep the bed for the edging. If you are installing a material, such as masonry or rubber, don't install it just yet.

Step 5. Prevent Weeds

The biggest drawback to a mulch bed is pulling weeds. There are a couple of techniques that we employ to help minimize weeds and to prolong the amount of time before they begin to pop through the mulch.

With the soil exposed and the bed cleared of all vegetation, we apply an organic pre-emergent. Our choice pre-emergent is corn gluten meal. It's safe for pets and kids and isn't going to hurt the tree. You can also install plants after applying corn gluten meal, but you won't be able to plant seeds.

The purpose of pre-emergent is to prevent seeds from germinating. It's a good idea to install pre-emergent under mulch because you just disturbed all the weeds and grass, and easily could have knocked some seeds into the soil. The pre-emergent will prevent those seeds from germinating.

Remove all the vegetation from the area to be mulched, then install pre-emergent.

After the pre-emergent is down, install a high quality weed barrier. We use, and recommend, a 4 or 5 ounce woven weed barrier fabric, but you'll only be able to find it at specialized stores. The stuff you get at the large retailers is not going to work, unfortunately. It's important to get a heavy weight and to ensure the fabric is woven. This increases the strength and longevity of the material, and allows water to drain through. If you can't get your hands on a good, high quality weed fabric, cardboard is fine. Cardboard will break down quickly, though, so you'll find yourself weeding earlier than if you use good weed barrier fabric. You might as well not install anything rather than wasting your money on a cheap, inferior fabric.

Avoid the temptation to install plastic. We never install plastic in mulch beds because it does not drain water, which means the roots aren't getting surface water, effectively killing the tree.

To properly install weed barrier, cut it in a circle a little larger than the dimension of your mulch ring. You want to install your edging ON TOP of the weed barrier. Next, slice one half of the circle from the outer edge to the center. From there, cut a circle out of the middle that is slightly larger than the tree trunk. It's okay if the weed fabric is not tight against the tree. The slit will allow you to install the fabric around the trunk, and the circle you cut out in the center will allow the fabric to lie flat on the ground around the tree trunk. TIP! The fabric comes in a roll, so it wants to curl back up instead of laying flat. Install it with the curl DOWN and it will hold itself in place without being able to curl back into a roll.

Cut your weed barrier in a circular shape with a slit for easier installation.

Step 6. Edging

If you are installing an edging material, now is the time to install it. Follow the manufacturers instructions and make it as pretty as you can.

Step 7. Mulch!

Probably the funnest part because now you get to see the fruit of your labor! This is the step where you use the final two digits in the 3-3-3 rule: Install your mulch at least three inches deep and keep it at least three inches away from the trunk of the tree.

Most trees have a portion of their roots exposed above the soil near the trunk. DO NOT COVER this portion of the roots! These roots are designed to be exposed to the air, and will kill the tree if buried. Likewise, clumping mulch around the base of the trunk, in what is called a "mulch volcano," will rot the base of the trunk. Now you have a dead or dying tree that could fall!

Dump the mulch into the bed and spread it out. You can use your hands or a metal rake to evenly spread the mulch. Get it at least three inches in depth, but four inches is better. The depth of the mulch is what helps to keep weeds from growing. It's usually preferred to have the mulch taper down from the near the trunk to the edge of the ring, so the mulch is thinner at the edges of the ring. There's no wrong way to taper the mulch, most people just like the way it looks when tapered from the tree outward.

Remember! Keep the mulch at least three inches from the base of the trunk!

Step 8. Completion!

Clean up the edging but be careful not to blow, sweep, or rake grass clippings and other debris into your fresh bed of mulch. Nothing will make the mulch look worse, and irritate you more, than ruining the pleasing aesthetic of new mulch with debris all over it! To give the installation a professional appearance, trim any portions of the weed barrier that are visible outside the edging. Smooth out the mulch with your hands so it's laying evenly.

This client preferred a live edge. Be sure to dress up your edges and trim any exposed weed barrier. Don't forget to leave a few inch gap between the mulch and the trunk of the tree.

Stand back and admire your hard work! Then snap a photo and post it to social media! Please tag @UncleOnionsLawn so we can admire it, too!

Installing a mulch ring around a tree is an easy, inexpensive way to make an otherwise bare area of your lawn look much better. When done properly, it's not only pleasing to the eye, but good for the tree. With a high quality mulch, it should look good for at least a year, if not two. With periodic maintenance to keep it free of weeds and debris, your new mulch ring is something you can be proud of.

Make sure to swing by every Monday morning for fresh blog posts packed with tips on lawn care, organic lawns & gardens, electric mowing, and everything related to keeping your lawn healthy and gorgeous! Aaron Johnson, the owner of Uncle Onion's Electric Organic Lawn Care, writes and researches all our posts. We might use AI to brainstorm ideas and help with editing. All articles and images are copyrighted and belong to Aaron Johnson & Uncle Onion's Lawn Service, LLC. Feel free to use them!