Is your lawn interrupted by one or more ornamental trees? How's the health of your lawn within the root zone of the trees? Chances are, it's struggling, and if you are able to keep it healthy, you may be spending more energy on it than the rest of your lawn requires.

Very few trees provide a good growing environment for the typical American lawn. They hog the resources, and mown lawngrass is a resource-greedy plant. They cast shade, and lawngrass is a sun-lover. They drop leaves, and though a thin layer of leaf mulch can be beneficial to the grass, unmulched leaves can block sun and water and cause dead spots in your lawn.

Not only is the pairing of lawn and tree hard on the lawn, but it's usually hard on the tree as well. String trimmers can damage bark, which weakens the tree's resistance to pests. Mowing over exposed roots can cause the same kind of damage. Then there's competition with the grass for resources, and possible negative effects from lawn chemicals, which are designed to meet the needs of grass, not trees.

Is it worthwhile to extend the lawn right to your tree's trunk? If you're having doubts about it, consider one of these other planting options for the area around your lawn tree.

Tree Island with Groundcover

It doesn't have to be fancy; it doesn't have to look much different than lawn. If the form of your tree is spectacular and you enjoy seeing the entire trunk as well as the branches, plant low perennials around it and leave it at that. There are groundcovers that will work for any environment. You may want to buy one each of several species, plant them, and after a year decide which you like best, then plant more of it. Or intermingle a few species to create a living oriental rug under your tree.

• As long as you use a good mowing strip, a tree island makes a great place to plant some obnoxious herbs that overrun regular flower borders. Try a locally hardy mint—they like shade, can live in a wide range of soil types, and are often evergreen. Sweet woodruff and creeping thyme can also handle a variety of under-tree conditions, and their leaves also remain year-round, though woodruff's turn tan-colored and thyme's turn burgundy during the cold months here in zone 4. (Don't know your winter hardiness zone?)


• Seek out reputable nurseries that sell some of your local woodland plants. These shade-tolerant natives are well adapted to living under trees, and many of them are increasingly scarce in the wild. If your tree isn't native, it may create different conditions than do your native trees, so investigate before choosing your plants.


• If you don't want to be trimming the edges, avoid plants with runners and instead find clumpers that will spread slowly out from their centers but won't try to escape into your lawn.


• If your tree is a conical evergreen, you may want to try making a rock garden under it. All sorts of creeping plants and miniatures do well in an acidic, dry environment, and there are shade-tolerant plants as well as the sun-lovers in this genre.

Woodland Island

• In a formal garden, arrange concentric rings of shrubs and perennials around your tree, or make a square bed around your tree and fill it with perennials, then plant shrubs at the four corners.


• For a more natural look, plant shrubs of different sizes in a pleasingly asymmetric group around your tree, fill the gaps with perennials, then extend the perennials to the edges of the bed.


• You may want to balance the tree's bulk by planting a group of shrubs nearby, making an irregularly shaped bed that includes both tree and shrub group, then covering the floor of your new island bed with perennials.


• To tie your island bed into the rest of your garden, include some of the same species you've used in nearby borders.

You can find descriptions of locally hardy shrubs and perennials to use under your tree by consulting a regional woodland field guide. Here's a list of good field guides for regions of the U.S., but try your local university press or the gift shop at a nearby state park for more regional guides.

Savanna Island

Defined as a grassland with occasional trees, a savanna has been called humankind's preferred landscape. Indeed, a lawn with trees mimics a savanna, though the lawn contains different species and has different maintenance requirements than a natural grassland.

To create a savanna island, plant a mix of native grasses in a bed around your tree. The grasses should be compatible with the microclimate under the tree. You may do well to plant native savannah grasses.

Some trees (bur oak and jack pine, for instance) occur naturally in savanna and so are particularly well suited for this type of landscape. Others (maples, for instance) will outcompete most grasses unless they're sited in a fairly moist area.

Read an overview [PDF format, 30MB] of oak savanna structure, including a list of key understory species in a midwest oak savanna.

Read a brief discussion of pine barrens, including types and key species.

The Shape of Your Tree Island

• In an informal garden, use an irregular shape for maximum appeal. Try a long triangular oval, with the tree forming a pillar in the widest area of the bed.


• If you have a formal garden, you can make your tree island a circle, square, or other regular geometric shape.
  
  
• If your tree is near enough to a walkway, patio, or other feature that forms an edge of the lawn, consider designing your tree island to cut a corner off the lawn.


• A kidney shape might work well for two trees, if you locate the trees in the two wide areas. This shape can be either symmetrical in a formal garden or asymmetrical for a more natural look.


• If you're tying together several trees, make the bed wide enough to cover all their root zones, and let it narrow as it extends away from the grove on one or more sides.

How to Make a Tree Island

Step 1. Make a mowing edge around your island bed to keep maintenance low.

Step 2. Cutting off or digging up the lawn under your tree may damage the tree's roots and jeopardize its health. Instead, consider smothering the lawn under it to create your new bed.

Different trees can tolerate different amounts of mulch. For clues, notice how thick the tree's natural leaf litter is. Does it drop tiny leaves that quickly decompose (locust or ash, for instance)? Then don't add more than a couple of inches of mulch. Is it a heavy shedder (a maple or oak)? Then you can add more mulch. In fact, smother in the fall and don't rake up the leaves; they'll add to the mulch nicely. You can either smother over the top of the leaves or smother first and let them fall onto the mulch.

Step 3. Plant through the mulch.

Want a tree island but don't have a lawn tree? Don't just plunk a sapling down into your lawn... design a bed that includes one or more trees with other plantings around them. You'll instantly add a beautiful feature to your garden that will generate interest even while your tree's not big enough to notice. Your tree will start out healthier because it won't be competing with your lawn, and your lawn will remain healthy and easier to care for instead of slowly becoming more demanding as your tree matures.

Keep in mind as you design that your new tree island isn't just a good alternative to an unhealthy or high-maintenance patch of lawn; it can also provide a focal point for your garden, habitat for birds and other wildlife, and increased privacy.