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What to plant under trees in your landscape
Story and Photography by Jennifer Williams
As you walk through a forest, you may notice the layer of leaf litter and other plant debris covering the forest floor, but what you more than likely will not notice is the diversity of plants growing under the towering pines (Pinus spp.), oaks (Quercus spp.), and other ancient trees.
As I design landscapes for clients, either from scratch or updating existing plans, I like to remember those moments as I contemplate what should be under their trees; my preference is more than just mulch.
There are several factors that must be taken into consideration when choosing plants that will be growing under trees. First and foremost, the amount sunlight. Does the area receive sun in the morning, in the afternoon, filtered sun all day, or consistent shade? Choosing plants that will thrive in the available sunlight is essential for success. Next consider the root systems of the trees you will be planting under. Minimizing damage to the tree’s roots will not only keep your tree healthy, but also enable your new plants to thrive. When planting, dig carefully, remembering that a tree’s roots generally grow out as far as the tree’s drip line. If your trees have large roots near or at the surface, be careful – don’t cover them with too much soil or mulch and choose companion plants that have smaller root systems to reduce competition. Finally, consider the water and fertilizer needs of the plants you are adding. Acid-loving azaleas (Rhododendron spp.) and pine trees are a great combination, as the soil beneath the pine will be more acidic than that that under a burr oak (Q. macrocarpa). Make sure to pair water-lovers and drought-tolerant species accordingly.
Four Planting Plans:
1. Y-Shaped Canopy
Here in Louisiana, this primarily applies to crapemyrtles (Lagerstroemia spp.), but also trees with higher canopies that place the area underneath in the category of partial sunlight. This is the by far the easiest level of exposure to work with. When working with this plan, place taller plants closest to the trunks and then downward and outward with smaller plants to ground covers. Options for this situation include daylilies (Hemerocallis spp.), Iris, Liriope, smaller ornamental grasses, Shasta daisies (Leucanthemum x superbum), yarrow (Achillea spp.), Coreopsis, and various annuals.
2. Shallow-Rooted Deciduous Trees
Spring-blooming bulbs are great additions for these areas – they will thrive in the sun before the tree canopy leafs out; then the foliage will fade away and can be cleaned up before adding fresh mulch in late spring. Hyacinth (Hyacinthus spp.), Narcissus, Crocus, and others are all great for areas like.
3. Tall/Established Trees with High Canopies
These trees are often those that were planted before your home was built and will be grouped in a more natural way, not equally spaced. You can have a beautiful display of blooms and foliage spring through fall in these areas by taking your cues from nature. Great plants for these areas include Hydrangea, azaleas, ferns, and hellebores (Helleborus spp.). You can plant sun-loving annuals or spring-blooming bulbs at the very edge of the canopy line to add brighter color.
4. Ground Covers and Annuals
If you prefer a more traditional look, and one that requires minimal upkeep, consider a variety of ground covers. Asian jasmine (Trachelospermum asiaticum) is a sturdy, evergreen option that will keep weeds at bay, but will try to push its boundaries; planting it where sidewalks or driveways will prevent it from reaching your lawn will help. Ajuga is another fantastic option with many varieties to add texture and color to the landscape while remaining very low maintenance. The most traditional look is a planting of annuals in a small bed surrounding your trees. This adds interest while requiring minimal maintenance.
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Additional mulching tips:
When planting under your trees is not an option, make sure you are mulching correctly. One of the worst things you can do is pile mulch up the trunk of your tree, creating what’s called a “mulch volcano.” Proper mulching keeps the mulch several inches away from the trunk.
When mulching new plantings, consider using a more natural look, i.e., shredded leaves under oaks or pine needles under conifers.
When using hardwood mulch, make sure to purchase high-quality mulch free of pest infestations that has been aged, but has not broken down too much.