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When Natives aren’t Nice

Native plants can act like invaders

Most gardeners would like to do a little less routine yard maintenance and spend more time being creative, or even relaxing. But the low maintenance garden, while a seductive idea, is not always easy to achieve. 

It’s partly a matter of design decisions and the materials you use. If your starting point is an existing garden, you can make it a bit easier to care for by paying attention to where you spend most of your uncreative time, then eliminating or modifying the features that create the demand.

Cracks between pavers, complicated lawn patterns and poorly laid gravel paths are notorious time wasters.  

What you plant makes an even bigger difference. Things that don’t need dividing often, for example, and plants that don’t self-sow like crazy consume less of your time than those that do. And you want to avoid plants with running roots, or at least be very careful where you plant them. 

When naturalists use the word “invasive” they are usually referring to introduced, non-native plants that threaten natural habitat by reproducing at the expense of native species. Gardeners often use the word in a different sense, to describe garden plants that want to expand way beyond the space the gardener had in mind for them. 

I did not fully realize until we moved to our present house and garden that there are quite a few native plants that can offend in this way. One of several reasons we relocated was my wish to make a native garden, and I had a head start: The former owner had planted a few natives herself, including a vine maple, some snowberry, native ferns and coltsfoot (probably Petasites frigidus).

One of those ferns, unfortunately, was bracken fern. I had no idea how fast bracken could travel until we smothered the surrounding turf with newspaper and a nice layer of organic matter. I’ve been fighting it ever since, and I am not winning. 

The snowberry spreads relatively slowly and doesn’t bother me so much, but an initially demure-looking clump of coltsfoot is steadily consuming the more desirable natives I planted around it. 

Predictably, I made a number of mistakes myself. Having learned that Nootka rose could spread aggressively, I chose Rosa gymnocarpa which, it turns out, is just as bad.

I also planted a number of grasses, including blue wild rye (Elymus glaucus) that I had admired in a friend’s front garden. I thought I could stop it self-sowing too much simply by cutting it back in early summer, but it responds by producing another set of flowering spikes. Now it’s everywhere. 

At my spouse’s request, I also planted a couple of quaking aspen. They seemed a perfect fit for our rather wet front yard. Within a few weeks, a friend who lives in my neighborhood (an area I’d dubbed the Aspen District even before I moved here) dropped by to share with me her nightmarish experience with aspen in her own yard. 

Here’s the short version: After a few years of aspen growth the soil in her small yard had filled up with aspen roots — and sprouts — to such an extent that in order to have any kind of viable garden, she was forced to have a contractor excavate, at great expense, a large volume of soil and roots. She still had to deal with a lower level of sprouts, eventually following up with 2-4-D herbicide on the stragglers — a tough decision for an organic gardener. After all that she still had to worry about roots invading from neighboring yards. She has since moved.

In some respects, aspen is an ideal tree for our area’s wet winters and dry summers, and in most yards, apparently, it behaves much less aggressively. It is in the nature of aspens to produce sprouts, or suckers, at some distance from the trunk. If you cut off an individual sucker, that sucker will not sprout again from the cut stump, but there will always be more suckers.

That’s how aspens form those picturesque groves we see in mountain seeps. When aspens are grown in turf, the young suckers can be mown off, and are not usually too problematic. 

Why did my friend’s aspens sucker so aggressively? She is, like many of us, a very active gardener, digging, planting, and moving things around frequently, no doubt disturbing aspen roots in the process. “Nick a root, make a shoot,” perhaps. And she grew vegetables in her yard and watered regularly in summer. That abundance of summer water was probably a big factor. 

Given how wet our garden is, I whisked my own aspens out of the ground soon after hearing my friend’s story. But I’m nervously watching two young specimens growing across our alley, just feet from my vegetable beds.

Rachel Foster lives and gardens in Eugene. She can be reached at rfoster@efn.org