Alternatives to Invasive Species by Bill Cullina (Original text copyright © New England Wild Flower Society 2003)
Of the 2814 species of plants growing wild in Massachusetts, fully 45% (1276 species) have been introduced (either on purpose or by accident) from other parts of the globe. Many of these are agricultural weeds that began arriving in grain or ship’s ballast soon after European colonists came here in the early 1600’s. Others were introduced by horticulturists or the federal government for use in gardens or soil stabilization, reforestation, and the like. It is impossible to know what effect this monumental immigration has had on native plants and animals. Certainly, of the thousands and thousands of plants introduced in the US and Canada from abroad, only a small number (estimates range from 3-7%) are thought to pose a serious threat to native ecosystems. These problem few are quite a problem, however. These invasive exotics have few if any natural predators to keep them in check, instead running rampant and displacing entire communities of native plants as well as the insects, fungi, birds, mammals, reptiles, bacteria, etc that have come to depend on them…. Invasive species have the potential to completely alter habitats, disrupt natural cycles of disturbance and succession, and most importantly, greatly decrease overall biodiversity, pushing rare species to the brink of extinction. Many ecologists now feel that invasive species represent the greatest current and future threat to native plant and animal species worldwide – greater even than human population growth, land development, and pollution.
It is high time that we horticulturists recognize our responsibility to both cease the importation and introduction of new and potentially invasive exotic plants and to stop growing and planting known or suspected invasives regardless of their ornamentality or consumer demand. I believe that we need to adopt the precautionary principle as far as plant introductions are concerned, and assume a species (including all of its cultivars) is invasive until proven otherwise (rather than the current approach of “innocent until proven guilty”). At least let’s not make this situation any worse.
Let's make a pact - let's try to avoid planting these plants this year.
1. Akebia quinata (Akebia). Anyone who has planted this vine heartily regrets it within a couple of years. Luckily, its not quite as tenacious as some of the invasive vines, so if you catch it early before it becomes too woody you can pull it out of trees and shrubs.
Instead, plant a vine on the pergola that’s an annual. Most vines grow fast enough to give some coverage by the summer. And, after all, the pergola is meant to provide shade in and of itself. If you want a perennial vine, its best to stick with Wisteria frutescens (American Wisteria).
2. Berberis thunbergii (Japanese Barberry) and Berberis vulgaris (European Barberry). Yes, its on the NYS Invasives list now, and already was considered to be invasive in CT. And yes, lots of people including old-school landscapers, nursery personnel and even at least one of my friends claim that the cultivars that have colored foliage (burgundy; gold; red) are not invasive. I’m skeptical, and favor the Bill Cullina approach of assuming they’re invasive until proven otherwise. There’s a fair amount of money and effort in NYS going into studies of some of the nicer barberry cultivars to show that they are not invasive so they can be grown and sold again.
People use barberry for a few reasons, mainly because it’s deer-resistant and has colored foliage. Plus some of the burgundy cultivars, like ‘Concorde’, remain small and compact – others, including ones with gold foliage, are pillar-shaped providing uprights in the design. And barberry was inexpensive.
To substitute for burgundy-colored barberry we tend to use either smokebush or ninebark. Neither of those is as reliably deer-resistant as barberry was, in my experience. Both can be cut back hard if needed – so you can keep them small. A more deer-resistant purple foliage plant is ornamental grass. There are some cultivars of Panicum that read “purple” throughout most of the season – they’re upright and as an added bonus they add motion to the garden. But if your intent was to have groups of small shrubs with purple foliage near the front of a fairly formal border or on the ends, none of these choices will really satisfy you. You may have to turn to purple-leaved Heuchera cultivars – although of course those have their own brand of finicky as well. Other perennial suggestions are burgundy-leaved Ajuga cultivars, Penstemon digitalis ‘Husker Red’ or ‘Dark Towers’, Actaea simplex atropurpurea cultivars like ‘Brunette’ or ‘Hillside Black Beauty’, Lobelia cardinalis ‘Fried Green Tomatoes’ or Hypericumandrosaemum ‘Albury Purple’.
Penstemon digitalis 'Husker Red'
3. Buddleia davidii (Butterfly Bush) and B. alternifolia (Alternate-leaved Butterfly Bush). It’s a beautiful shrub when it’s in flower, there’s usually a butterfly on every single flower and it grows fast and flowers on new wood so you can cut it back every single spring. Chickadees eat the seeds in winter. Its inexpensive and takes up a fair amount of space – excellent bang-for-buck in summer gardens. But it’s also invasive. And if you look at the “Bringing Nature Home” information, you’ll see that it serves as a host plant for only one species of butterfly. Compare and contrast – clover serves as a host plant for 122 species of butterfly. Better to leave a little clover in your lawn and plant some nectar-rich perennials.
If you want a summer-flowering shrub with excellent flower power try Lagerstromia or Hibiscus syriacus. Most of the newer Rose-of-Sharon cultivars are triploid – meaning they can’t set seed so you won’t have a forest of R of S like in the olden days. Other ideas include Hypericum (shrub form), Hibiscus moscheutos, Heliopsis helianthoides, Aster and Goat’s Beard. Of course, ornamental grasses can also be used for late summer interest.
4. Hedera helix (English Ivy). No, no, no! Don’t do it! Once its spread all over the whole landscape its virtually impossible to remove. It will rot your fence, engulf your trees and grow into your brick façade. In general, using vines as ground covers is usually not the greatest idea because they will be hard to keep in check. If you want a beautiful ornamental vine that does somewhat less damage but is much easier to manage, try Hydrangea anomala ssp. petiolaris (Climbing hydrangea). You can let it creep along the ground, and it makes a lovely ground-cover. Its relatively easy to pull off the house if you want to. It can make chain-link fence completely disappear – but don’t try to remove it from a chain-link fence because it is quite two-dimensional and will wind back and forth extensively.
5. Ligustrum species (Privet). Yes, it’s invasive, so we need to stop planting privet hedges and use other types of plants instead. Privet is “traditional” and “classic”, not eaten by deer and inexpensive. It has an upright habit and is grown especially for use in making hedges, so its really easy to get a row of uniform plants of just about any height to create an “instant” hedge. It can be readily renovated, so, again, you can keep it manageable.
Almost any shrub can be made into a hedge, especially if you plan ahead – with the caveat that plants should be spaced so that they grow to be a hedge over time. Page Dickey told us about using ‘Miss Kim’ lilac as a hedge. We’ve seen lots of pictures where ornamental grasses are used as a hedge. If you have no deer, you can use Taxus or Manhattan euonymus as a hedge. Some shrub roses can be hedges. Evergreen choices include Ilex glabra (Inkberry Holly, Prunus laurocerasus (Cherry Laurel), Leucothoe, Rhododendron and Leatherleaf Viburnum.