Overcoming the problem of planting under trees

Story and Photos by Katharine Musso

We’ve all seen those meticulously groomed lawns with one or more handsome specimen trees dropped seamlessly in the emerald green seas of turf. Maybe we saw it in a movie or maybe we saw it across town. What we do not see is the time, money, frustration, and effort that go into maintaining the illusion that lawns and trees work well together. In your own yard, as you plan every year with hope and amnesia regarding prior failures, you’ll more than likely end up with bald patches or outright failure when growing turfgrass smack dab under a mature tree. So, you ask, if grass is so difficult to grow, what are my alternatives? Happily there are many, but they may require a slight adjustment to your approach.

Trick the eye by planting a colorful garden right outside a tree’s drip line.

First, let’s start with the tree. A tree is not a garden ornament, but rather a living plant with its own light, water, and nutrient needs. Some are evergreen; others will lose their leaves for a season or more. Some trees send roots deep below the surface while others are rooted shallowly, near the soil surface. When a tree has graced the landscape for several seasons we tend to take it for granted, but before planting near or under it we must consider the tree’s needs. Apple (Malus spp.), cherry and plum (Prunus spp.), and silver maple (Acer saccharinum) trees all resent disturbance to their roots. Southern magnolias (M. grandiflora) and red maples (A. rubrum) are examples of trees that are a little bit more forgiving. Pine trees (Pinus spp.) create special growing conditions by virtue of the acidity of their needles and the dry conditions under their dense boughs.

The obvious solution to the difficulty of planting right up to a tree’s base is to avoid doing so altogether. A ring of bright, thirsty, annuals planted within a tree’s drip line can produce unfortunate results. All trees exchange oxygen and other gases in the air pockets that surround their root structures in the soil. In an effort to keep heat-fatigued annuals looking fresh, you can overwater the tree, filling those gaps with water, which would prevent that gas exchange. Over time, this can literally drown the tree. Younger trees and shallow trees are particularly susceptible to this. 

Autumn ferns provide an appealing woodland effect.

To give the impression of a flowerbed under a tree’s canopy, you can use the landscape designer’s trick of trompe l’oeil. Plant a garden bed immediately outside the dip line with brightly colored smaller plants in the foreground with taller plants toward the back. The eye goes from low to high, front to back, with the tree completing the tableaux. The impression is that the garden extends directly to the tree, but in fact there is a well-mulched stretch of anywhere from 3-7 feet between the bed and the trunk, depending upon the height of the tree.

While we’re speaking of mulch, few things tidy up a garden quicker than an application of fresh mulch. Before taking on a planting project under a tree, ask yourself if you wouldn’t be satisfied with a fresh application of mulch every season. Take a close look at the yards and gardens you admire and you might find the common element of neatly applied mulch around each tree. But don’t go overboard. The mountains of mulch that you see at the base of a parking lot tree is not only unsightly, but can harm the tree by smothering roots and preventing uptake of nutrients. 

Mondo grass is a better alternative to more invasive ground covers.

If you’re intent on planting, identify your greatest need. If a deciduous tree looks forlorn while leafless in the spring, consider planting small bulbs for a woodland effect. Muscari, snowdrops (Galanthus spp.), Oxalis, and miniature daffodils (Narcissus spp.) will provide pleasing small drifts of color and fade when the tree has leafed out and no longer needs ornamentation. After the tree has leafed out, perhaps nothing more is needed for the growing season.

For those who like a display for most seasons, ground covers are often the best choice. You will often find vigorous ground covers recommended for bare spots under trees. It makes sense that a fast-growing, tenacious plant could fill in a hole quickly. Unfortunately those same characteristics make some frequently recommended plant choices highly undesirable in your yard. Both English ivy (Hedera helix) and periwinkle (Vinca major, V. minor) are classified as invasive plants that should be avoided in the Alabama landscape. Another familiar ground cover, Liriope is on the suspected invasive list of the Alabama Cooperative Extension Services. Mondo grass (Ophiopogon japonicus) is an attractive alternative that behaves in the yard and prefers partial to full shade.

Mulch is sometimes the simplest and most appealing solution.

Ferns and Hosta are beautiful plants in their own right and are attractive plantings near trees. A small glade of ferns makes a lovely naturalistic feature for a woodland effect. Autumn fern (Dryopteris erythrosora) grows well in light shade, planted in the loam of fallen deciduous tree leaves. As with ferns, there are a wonderful variety of hostas to choose from: blue, variegated, miniature, and giant. 

Whatever your choice of plant materials, use care when planting to minimize root damage. Avoid disturbing significant roots; look for individual planting holes in which to tuck small plants or bulbs.

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