What to Plant Under Trees

One of the most commonly asked questions about gardening is what to do about the areas under trees. 

It seems like those shady, dry places around trees bother gardeners who would like to have their gardens pretty to look at from every angle. 

Not only is the soil dry under trees since trees quickly drink surface water, the roots are dense and do not allow room for digging. On top of all that, digging around tree roots can damage the health of the tree in the long term.

Sometimes we see flower beds planted around trees and that solution can work quite well as long as it is a bed full of perennials and the plants are in the ground rather than in a raised bed. Raised beds planted on top of tree roots can smother the tree’s roots, stunting the growth and shortening the life of the tree.

The first rule for healthy plants under trees is to completely avoid annual plants such as begonias and petunias that absorb water and nutrients needed by the tree. Each spring or fall when annuals are planted your trees’ roots are being torn and cut. Also, annual plants have shallow roots and require more frequent irrigation than is healthy for the top roots of trees.

The ideal solution is to plant long-living groundcovers and other perennials around the drip line of young trees at planting time. Over the years, the young tree’s roots will fill in around the ornamental plants’ roots and they will find a healthy growing situation together.

And, planting under trees it is best to purchase small perennials rather than gallon- sized containers.  

The smaller root ball in a 4-inch plant will require a smaller hole and do less damage to the tree roots. Yes, it will take an extra year to fill in the space but a light mulch cover will keep the area looking good, help the soil retain moisture, and give both plants a better chance.

There are dozens of perennial plants that thrive under trees. Look for native perennials that want dappled, part-shade or full-shade. Native perennial selections are better adapted to your local soil types, rainfall, heat and humidity patterns.

As a rule of thumb, avoid plants that are Japanese, Chinese, Korean and Asian in origin. Most of these plants spread fast in our soil and weather, quickly becoming a problem that has to be managed under trees. 

Examples of popular plants in this potential-problem category include: Bamboo, Chinese Wisteria, Japanese Callicarpa (beautyberry), Japanese privet, Asian jasmine, Japanese honeysuckle, etc. English ivy also quickly becomes a problem plant, choking tree roots and trunks.

Fall planted, spring flowering bulbs are compatible with tree roots. Select the tiny daffodils, hyacinths, crocus and snowdrops that do not need to planted deep and prefer the summer dry soil.

Rhododendrons and their cousins Azaleas also enjoy dappled light but their roots need to be kept moist, so their root balls should be planted farther out by the tree’s drip line which is located at the end of the trees’ branches. Hostas and cold-hardy begonias are other great selections for that area.

Native, perennial, woodland, wildflowers thrive under trees and live compatibly close to the trunks. 

Those possibilities include: Toothwort (Cardamine concatenata), Bloodroot (Sanguinaria candensis), Wild Ginger/Snakeroot (Asarum canadense), Virginia bluebells (Mertensia virginica), white trout lily (Erythronium albidium), May apple (Podophyllum peltatum) and sharp-lobed hepatica (Hepatica acutiloba), Phlox divaricata (native or wild blue phlox), American Alum Root (Heuchera Americana) Jacob’s Ladder (Polemonium reptans), Allegheny Spurge (Pachysandra procumbens), etc.

Sources: Area Farmers’ Markets, plant shows, Grogg’s Green Barn in Tulsa (groggsgreenbarn.com)

Mail-order: Prairie Nursery www.prairienursery.com, Pine Ridge Gardens www.pineridgegardens.com, Missouri Wildflowers www.mowildflowers.net