Grow 528: Keep invasive plants out, ivy, ants and plants


Curtail the spread of ivy and myrtle with a perimeter path


Dear Janet,

You wrote about keeping invasive plants from crossing into your yard by putting plastic into the ground like a buried wall. Wrong! I've tried that to keep out myrtle on one side and English ivy on the other. That edging doesn't even slow them down.

Don't print my name or city. My neighbors mean no harm.


Dear A.,

You're right. But we're discussing two different kinds of plants. Sorry for the confusion.

I wrote about "...running-root invasive plants (like Mexican bamboo)" on July 26. Myrtle (Vinca minor) and English ivy (Hedera helix) are in another group, of plants that do most of their spreading by creeping across the surface. Beneath branches that sprawl beyond the established colony the soil stays moist, cool and dark -- perfect conditions for this kind of plant to form roots on the underside of the stems.

Other groundcovers that spread primarily above ground are wintercreeper (Euonymus fortunei), ajuga (A. repens), strawberries, barren strawberry (Waldsteinia fragarioides), thyme and creeping phlox (P. subulata). A number of weeds travel the same way, notably ground ivy or creeping charley (Glechoma hederacea) and poison ivy.

To bar these overland creepers use a horizontal barrier, such as a perimeter path as wide as the branches tend to grow. Cut interlopers regularly or spray them with herbicide before they root.

Short reports

When ivy fails

D.W.  needs help with large areas of groundcover ivy that have thinned and become infested with weeds.

All plants get old, and have bad years. Yours is old if it's been there ten years or more, and this year all evergreen ivy had a tough winter. When they die out, bare spots develop where other plants can get started. Kill or dig out the weeds -- and the ivy they're tangling with. Loosen the soil and add compost. Plant new starts, mulch the area and keep it weeded and watered until the replacements fill in.

Switching to another groundcover species. or a quilt of two or three, is not a bad idea, either.

Perennials can stand in for shrubs

G.C. is realizing that a mystery plant she thought was a shrub is just a very large perennial. It happens, G.C.! Many perennials can stand in for shrubs, so long as you don't need a woody presence in winter. Some perennials that rival shrubs in size and blow them away for summer show are Joe Pye (Eupatorium purpureum), ironweed (Vernonia species) and blue globe thistle (Echinops exaltatus).

Ants and plants can coexist

P.S.  and others have noticed ants in abundance this year and wondered what to do. The answer is probably, "Nothing."

Ants belong in the soil and can coexist peacefully with plants. Sometimes ant numbers can be so high that the tunneling causes roots to dry but then it's not ants you'll wonder about but wilting plants. Some types of ants "farm" aphids, even moving them between plants, but that's not the main source of aphids.

If you grow aphid-prone plants, whether you see ants or not, you should hose the plants frequently with a hard spray of water to keep the aphid numbers down.

Can that ash be saved?

B.M. wants to know if an ash tree can be saved from emerald ash borer with injections.

There are no guarantee except that whatever you do in the way of protection you will have to keep doing every year. If you have a very important ash tree that shows absolutely no sign of emerald ash borer damage you might call a tree care company about injections in spring or spraying in summer. Yet by the time the average person notices damage, it's too late to treat.

We're taking down more than a dozen ashes for my in-law's today -- I'm probably cutting and dragging wood as you read this. Then we'll plant substitutes. I feel it's the best answer, considering the continuing cost of treatment and the fact that no reliable results exist to determine if any of the possible protocols work or how well.


Green thumbs up

to learning from what grows well on highway shoulders and medians. Scholar trees (Sophora japonica- how nice to see white flowers in August!) thrive in the median , so you know they don't need coddling in terms of water, fertilizer and weeding. You can also guess that low, scrambly fragrant sumac (Rhus aromatica), surviving and spreading among aggressive roadside weeds, may be more that you ask for -- an invasive in a "normal" garden.


Green thumbs down

to people who dump non-compostables at yard waste collection sites. Stern looks, too, to those who see but don't immediately report this to the site manager. Most such sites are tax subsidized and our only link to low cost compost and freedom from making compost ourselves. Don't ruin it for all of us by being too lazy to bag and drag curbside things that will ruin the site's shredding equipment, devalue the compost, raise the price or end this service.


Originally published 8/9/03