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The Garden Decoder: What Is a ‘Soft Landing’?

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The Garden Decoder: What Is a ‘Soft Landing’?

April 27, 2023

To celebrate Arbor Day this Friday, April 28, plant a native tree. Better yet, make it a keystone species, and then surround it with a “soft landing” to provide a welcoming spot for pollinators. Heather Holm, pollinator conservationist and award-winning author, and Leslie Pilgrim, founder of Neighborhood Greening and editor of the Butterfly Effect, developed the soft landing concept to give gardeners an easy and approachable way to help pollinators at home. They need it: More than 40 percent of our insect species are declining globally, according to a 2019 study. “People know things are falling apart and they want to help,” says Pilgrim. “But they don’t know how to start. Planting a soft landing beneath a native tree is a simple garden project with a really big impact.” Not to mention, it’s beautiful. Holm and Pilgrim show us how.

Photography by Heather Holm, unless otherwise noted.

What is a “soft landing”? 

The soft landing plants beneath this native maple tree include flowering pink wild geranium (Geranium maculatum), foliage of Zigzag goldenrod (Solidago flexicaulis), Smooth Solomon’s Seal (Polygonatum biflorum), and white-flowered Viola canadensis. Photograph by Vicki Bonk.
Above: The soft landing plants beneath this native maple tree include flowering pink wild geranium (Geranium maculatum), foliage of Zigzag goldenrod (Solidago flexicaulis), Smooth Solomon’s Seal (Polygonatum biflorum), and white-flowered Viola canadensis. Photograph by Vicki Bonk.

A soft landing is a diverse mix of herbaceous native plants grown underneath the dripline [see below for more on this] of a native, preferably a keystone, tree. “These plantings provide critical shelter and habitat for one or more life cycle stages of moths, butterflies, and beneficial insects, such as bumble bees, fireflies, lacewings, and beetles. In addition to plants, soft landings also include leaf litter, duff [partially decayed organic matter], and plant debris. They also build healthy soil, provide food for songbirds and pollinators, sequester more carbon than turf grass, and reduce time spent mowing,” states Holm on her site pollinatorsnativeplants.com. “But it’s important to remember that soft landings only work with native plants,” adds Pilgrim. “You can’t do this with a random tree and a random groundcover.”

To create a soft landing, Holm and Pilgrim recommend a mixture of native perennials, sedges, and woodland grasses. “The planting style is up to the homeowner,” says Holm. “But for a tidier look, stick to plants that grow no taller than 24 inches tall, 18 inches is preferable.”

What is a “drip line”?

“A drip line is the extent to where branches come out from a tree. Go to the farthest branch out, and then “draw” a vertical line down from it,” says Holm. “That’s the tree’s drip line.” Adds Pilgrim: “I think of it as the tree’s umbrella.”

Why are keystone plants important? 

An American linden (Tilia americana) grows above a sea of understory plants: Virginia bluebells (Mertensia virginica), white Trillium grandiflorum, bloodroot (Sanguinaria canadensis) foliage, and Jack-in-the pulpit (Arisaema triphyllum).
Above: An American linden (Tilia americana) grows above a sea of understory plants: Virginia bluebells (Mertensia virginica), white Trillium grandiflorum, bloodroot (Sanguinaria canadensis) foliage, and Jack-in-the pulpit (Arisaema triphyllum).

For the biggest biodiversity bang for your buck, plant a keystone species. “Keystones are native plants that support a significant number of caterpillars (butterfly and moth larvae),” writes Holm. Native oak trees, for instance, are a shining example: More than 940 kinds of caterpillars feast on them. After they’re done feeding, these future butterflies and moths finish their life cycles in the leaf litter and duff beneath the tree. According to the National Wildlife Federation (NWF), entomologist Doug Tallamy and his team at the University of Delaware discovered that 14 percent of our native plants support 90 percent of butterflies and moths. While horticulturalist Jarrod Fowler found that 15 to 60 percent of North American native bee species are pollen specialists who only eat pollen from 40 percent of native plants. To find the keystone plants in your region visit the National Wildlife Federation (NWF) site.

How do I get started? 

A white oak in Minnesota is surrounded with early meadowrue (Thalictrum dioicum), pinkish-purple wild geranium (Geranium maculatum), periwinkle-hued Virginia Waterleaf (Hydrophyllum virginianum), two grassy-like carex: (Carex sprengelii and Carex pensylvanica), and the downy yellow violet (Viola pubescens).
Above: A white oak in Minnesota is surrounded with early meadowrue (Thalictrum dioicum), pinkish-purple wild geranium (Geranium maculatum), periwinkle-hued Virginia Waterleaf (Hydrophyllum virginianum), two grassy-like carex: (Carex sprengelii and Carex pensylvanica), and the downy yellow violet (Viola pubescens).

“The ideal time to add a soft landing is when you’re planting a new tree or sapling,” says Pilgrim. “This way you won’t disturb the root system after the tree is established.” Opt for cell pack-size plants and plugs or use a native seed mix geared to your site. Holm and Pilgrim, with help from conservation scientist Desirée Narango and Tallamy, put together a handy list of soft landing plants—part-shade to shade loving natives—recommended for the Upper Midwest, Northeast, northern mid-Atlantic, and southern Ontario regions. “After you plant, water both the new tree and the soft landings well for the next several seasons to make sure there is enough water for everyone,” says Pilgrim.

If you want to create a soft landing beneath a mature tree, you first need to get rid of the turf grass. “Start site prep in the spring by putting down either cardboard or paper on the area of the dripline and weigh it down with pieces of wood or mulch,” says Holm. “This method will kill the turf grass so that you’re ready to plant in the fall. Or you can do this in the fall and plant in the spring: simply rake additional leaves into your new planting area and then do the cardboard and mulch lasagna layering to kill the turf grass.”

After you’ve prepped the site, fill in with cell-pack size plants or plugs. “Carefully and gingerly dig small holes with a small trowel,” says Holm. Do not use a shovel, which will damage the roots of a mature tree.

“For a very large tree, don’t plant any closer than 18 inches to the trunk because that’s where you have those really large primary roots,” advises Holm. “Start working from the drip line and then plant inward until you can safely still dig small holes.” Holm and Pilgrim recommend including plants that will spread so they can weave in through the space. “Vegetation with stolons like wild strawberry or groundsel will wander to fill in the space nicely,” says Pilgrim. “Or rhizomatous plants, like grass-like Pennsylvania sedge will weave through flowering plants adding softness and texture,” adds Holm.

“If it’s a huge mature tree in their front yard, you might only want to start by planting a third of the dripline. Then expand it if it’s working well,” says Holm.

Part of cultivating a soft landing is that you’re “building up organic matter passively by changing the way you maintain the area under tree,” says Holm. Leave any the leaf litter or plant debris that falls into your soft landings. This organic matter feeds the soil, which in turn feeds the plants and trees.

Plant Recommendations for a Soft Landing

Iris cristata growing above leaf litter. When looking for native species at the nursery, caveat emptor. &#8\2\20;Ask questions to make sure plants and trees haven’t been treated with systemic pesticides, which stick around for a while” says Pilgrim. While avoiding systemics, like neonicotinoids, is important for any plant, it’s especially so for soft landings. “You don’t want to create a nice viable habitat only to have it be a poisonous one,” says Holm. And, of course, don’t use any pesticides or synthetic fertilizers.
Above: Iris cristata growing above leaf litter. When looking for native species at the nursery, caveat emptor. “Ask questions to make sure plants and trees haven’t been treated with systemic pesticides, which stick around for a while” says Pilgrim. While avoiding systemics, like neonicotinoids, is important for any plant, it’s especially so for soft landings. “You don’t want to create a nice viable habitat only to have it be a poisonous one,” says Holm. And, of course, don’t use any pesticides or synthetic fertilizers.
  • Bellwort (Uvularia grandiflora) is a spring bloomer that showcases yellow bell-like blooms that are attractive to native bees.
  • Blephilia hirsute is a summer flowering woodland plant that produces pale blue whorled flowers on erect stems. Plant well-drained soils in areas that get full sun to part shade.
  • Bloodroot (Sanguinaria canadensis), one of the first spring ephemerals to bloom, features flowers with multiple white petals surrounding a yellow center. Attractive to native bees, who pollinate them, their seeds are dispersed by ants.
  • Wild geranium (Geranium maculatum) is beautiful ground cover with prolific purplish-pink flowers.
  • The compact wild iris Iris cristata produces purple flowers from spring through summer in shady, well-drained acidic soil. Hummingbird and bees will flock to it.
  • Sprengles sedge (Carex sprengelii), also known as long-beaked sedge, is a cool season species that produces wheat-like flowers in spring and again in the fall.
  • Common blue violet (Viola sororia) thrives in sun to part-shade. It self-seeds so will weave its way through an understory planting.

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