Sunday, May 5, 2013

Aggressive Native Plants Have Their Place

Aggressive plants are generally not popular. Many a curse has been spoken against them as a gardener has attempted to rein them in. Others folks simply declare them to be a “WEED” and tackle them with weed forks, shovels and chemicals. I’m here to say that aggressive native plants have a role to play in their local environments. Understanding them is key to deciding how they might fit into your space.

Trumpet creeper, Campsis radicans

While it might seem like these plants move in and take over the average garden space, there are specific benefits that they offer which can be considered: soil retention, support for pollinators, and food for songbirds and many other critters.

Soil Retention and Erosion control

Many of the aggressive woody plants can be found streamside. Their purpose is to create an extensive root system, usually by suckering, in order to hold the banks of a stream in place.

Hazel alder (Alnus serrulata)
These plants include hazel alder (Alnus serrulata), elderberry (Sambucus nigra ssp. canadensis), Virginia sweetspire (Itea virginica), yellowroot (Xanthorhiza simplicissima) plus many rushes (Juncus) and other perennials with thick roots. Invite any of these folks into a garden with rich soil and good moisture and you will have plenty to go around.

Many of the aggressive herbaceous plants (annuals, perennials, grasses) are early succession plants. Their purpose is to cover bare soil to hold it in place until woody seedlings can arrive.

Small's ragwort (Packera anonyma)
This is where you'll find many annuals like fleabane (Erigeron annuus) and ragweed (yes, it's native!), and aggressive perennials like asters (Symphyotrichum), yellow ragwort (Packera anonyma), violets (Viola), primrose (Oenothera), some goldenrod (Solidago), and grasses like broomsedge (Andropogon virginicus).

Weedy woody plants that move in later include pines (Pinus), sweetgum (Liquidambar styraciflua), maples (Acer rubrum for example), boxelder (Acer negundo), and black locust (Robinia pseudoacacia). These early colonizers can handle poor soil and, in some cases, such as the locust, even help to improve the soil.

Beautiful and fragrant Robinia pseudoacacia

Support for Pollinators

Doesn't that look like a feast?
Viburnum nudum var. cassinoides
Pollinators need a lot of flowers to get what they need. From the tubular flowers that support hummingbirds (Coral honeysuckle, Lonicera sempervirens, and Trumpet creeper, Campsis radicans) to the nectar-rich flowers that support bees, wasps, beetles and flies, our landscapes are not what they were 300 years ago. So much land has been reshaped to be subdivisions, businesses, roads, paved surfaces, and millions of acres of non-native grass (lawns).

Fleabane (Erigeron annuus)

 The roadsides, on the other hand, are full of the flowers these pollinators need - ragwort and fleabane are both blooming now. Later in the year the rambunctious Canada goldenrod (Solidago canadensis) and the asters (Symphyotrichum) will be there while virgin's bower (Clematis virginiana) scrambles over every shrub and fence. Their numerous and dense flowers provide much food.

Food for Songbirds and others

Numerous flowers often make for numerous fruits/seeds, a trait that is relished by many small creatures such as songbirds. Seed heads on plants like dog fennel (Eupatorium capillifolium), asters, maples, sweetgum, pines, sedges and grasses help determine how many birds can live in a certain area. I've seen birds peck at the dried legume pods on redbud (Cercis canadensis), a prodigious producer of pods in some years.
A spring flowering sedge (Carex)
is making seeds now

Tiny, numerous fruits on plants like black cherry (Prunus serotina) and elderberry might seem excessive to us, but they help support the birds we love long after their flowers supported pollinators.

Fruits that fall to the ground are gathered by small mammals like field mice - which then become food for hawks and owls.

Different plants have fruits/seeds throughout the year, allowing the birds and small mammals to find food as they need it. Nature takes care of the scheduling!

In the last few years people have become more aware of how native plant foliage supports birds by way of the insects that develop on the leaves. Most of the birds you don't see at your feeders are looking for insects to eat. They often find them as caterpillars on plant leaves. The black cherry that so many people criticize as a weed tree supports over 450 different species of Lepidoptera as a host plant. How many insects there are available to birds contributes to how many birds can live in an area.

Plant Virginia creeper for the birds
and enjoy the fall color too.

As you can see, many plants support birds two ways - by way of their fruits and also by the insects that feed on their leaves. Five-leaved Virginia creeper (Parthenocissus quinquefolia), often mistaken for poison ivy, has flowers for pollinators, tasty berries for birds and supports caterpillars of the sphinx moth (several species).

You can minimize plant aggressiveness using traditional gardening techniques. For aggressive seeders, deadhead some of the flowers before they go to seed. Mulch the areas around them to reduce the number of seeds that sprout. Pull up seedlings early when they are easier to dislodge.

For plants that sucker, site the plant appropriately either by only planting it where it can be allowed to sucker or by doing what you can to avoid root disturbance (some plants sucker more aggressively when their roots are disturbed by digging around them).

So if aggressive plants invade your space, think about what they can do for you before you tackle them. They might be just the ticket ....


  1. Fantastic post Ellen! I love many of these plants and have the space for them to grow and support wildlife in my garden. Thank you!

  2. Thank you for this blog...I love it! I learn so much with every post. :)

  3. Intrinsically, there is nothing wrong with aggressiveness. It helps to understand the way nature works. Succession is a normal process with invasive new-comers gradually giving way to slower-growing or late-arrival species. I am glad you pointed this out.
    It should not be confused with the invasive quality of non-natives that, having left all enemies behind, can spread uncontrollably wreaking havoc in habitats unprepared to handle such attacks.

  4. Love this post and totally agree that colonizing plants are important. In fact, they are essential in my garden.

  5. A great post - very educational!