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Ground covers are better than grass under trees

Plants in various shades of green with broad leaves growing under tree
July 1, 2019
Lawn grass is often disappointingly patchy or bare around trees.  In the shade beneath a tree’s branches there simply isn’t enough sun for grass to grow. 
Rather than struggling to grow turf in the shade, consider a better option: a ground cover. In the Arboretum’s Ground Cover Garden, you can see many examples of plants that will grow well under trees.
A ground cover looks better than patchy grass and reduces the lawn you have to mow. It’s better for the tree, too, because most ground covers will not compete with the tree’s roots for water and nutrients as much as turfgrass does.
Traditionally, plants used as ground covers have been low, creeping, and evergreen. Many, such as Japanese pachysandra (Pachysandra terminalis), periwinkle (Vinca minor), and English ivy (Hedera helix), can tolerate more shade than lawn grass can. Although their foliage may discolor in the winter, they usually keep some leaves all year. If they flower, it’s incidental to their appearance as a low, green carpet.  
However, any plant that can tolerate shade can cover the ground under a tree. It need not be evergreen. Flowering plants can serve as a ground cover as long as they have foliage that stays green and attractive through the season.
Hostas and ferns are popular choices, along with lungwort (Pulmonaria), Siberian bugloss (Brunnera), Canadian wild ginger (Asarum canadense), sweet woodruff (Galium odoratum) and bishop’s hat (Epimedium). 
If your tree allows some light to filter down through its leaves and branches, you may be able to grow cranesbill (Geranium), coral bells (Heuchera), or other part-shade perennials. For interest early in the season, try planting some of the more shade-tolerant spring-flowering bulbs, such as early daffodils, Siberian squill, snowdrops, and grape hyacinths, among your ground cover plants. 
For more help choosing ground covers, consult the Plant Clinic
It’s important to choose sturdy, long-lived perennials that will come back year after year. That’s because a tree’s roots lie near the surface of the soil, and digging in the area beneath a tree’s branches is likely to damage some of its roots.  
To keep soil and root disturbance to a minimum, plant durable ground covers just once and then leave them alone. Start with small plants, so you can dig smaller, less damaging holes. 
If you like having bright annual flowers under a tree, don’t plant them in the ground. The yearly digging will damage the tree's roots. Instead, plant shade-tolerant annuals such as begonias and impatiens in containers. Set the containers among the ground cover plants. To make sure water can drain away, elevate the containers slightly above the soil by setting them up on bricks, sticks, or pot feet.