Invasive plants need to be watched, controlled

In early spring, sweet violets (Viola odorata) bloom and fill the garden with heady fragrance. Now, in July, I’m curbing the take-over tendencies of this demure charmer by ruthlessly pulling up new seedlings and shoots.

I’ll have to keep a sharp eye out for both during the rest of the growing season if I want to control the number of violets in the garden. Is it worth it? Sometimes I wonder, but then I remember that wonderful spring fragrance.

My garden has a number of other plants with both invasive tendencies and desirable qualities. There’s lily-of-the-valley (Convallaria majalis), with those lovely little white bells and a gorgeous scent that promises warm weather. In July’s heat, I’m patrolling the garden looking for spreading new shoots. They regularly head out to explore the rest of the garden world instead of being content where they are.

Years ago, a friend gave me a start of the sweet woodruff (Gallium odoratum) from her garden. I planted it, admired and enjoyed it under the trees and rhododendrons each spring, and then forgot about it. What a mistake — ignored, it took over. All those tiny white flowers floating above the leaves turn into an incredible number of seeds and seedlings; new shoots from the roots are equally plentiful. Reducing the sweet woodruff to a manageable patch was hot work that summer.

You would think that the name—bishop’s weed (Aegopodium podagraria)—should have given me a hint. Unfortunately, I ignored that hint and planted it in my garden. It thrived, moving rapidly from one area into the next. While the variegated foliage is attractive, some of it wants to revert back to simple green and needs to removed. I decided to pull it all and be done with it. I haven’t missed this one, but it still pops up here and there just to remind me to be watchful.

Watchfulness pays off with quite a number of other perennials as well. Those attractive seed-heads that give cranesbill geraniums their name also spread the plants throughout the garden, and the dense but spreading root system on some varieties is difficult to dig out. Deadheading and shearing back after flowering helps to control rampant spreading and produces fresh green foliage and more flowers.

The snowdrop anemones (Anemone sylvestris) have spread way beyond the small clump another friend brought over some years ago. Some, I’ve dug up and discarded, but most of them I’ve kept. They’re just too cheerful in the spring to do without. Most years they opt for a sparser second bloom in the fall, too.

Lady’s mantle (Alchemilla mollis), blooms prolifically for most of the summer. When it starts to look tatty, I cut it back, and it starts all over again. It also seeds prolifically, so deadheading should be essential. The trouble is that I actually like the great clouds of blossoms turning into seed-heads—just not the result of letting them be. Oh well, they’re easy enough to pull out, and the newly sprouting leaves look like dewy little miniature fans.

I learned the hard way not to compost the seed-heads of invasive plants—they showed up all over the garden. Comfrey (Symphytum), feverfew (Tanacetum parthenium), spiderwort (Tradescantia), oregano (Origanum vulgare) and others survived the compost bin and re-established themselves. And so did goldenrod (Solidago). But I’m watching them now.

This week in the garden

Remove weeds and fading flower-heads from rapidly spreading plants before they go to seed.

Keep an eye out for those rapid spreaders and pull out any new seedlings or shoots.

Deadhead perennials and annuals to extend bloom.

Continue to tie plants to their stakes as they grow.

Continue to add to and turn the compost pile, adding finished compost to flowerbeds and vegetable garden.

Mulch—it protects the roots of plants, holds in moisture, and helps eliminate weeds.

Harvest potatoes, garlic and onions after tops yellow and die.

Raise mower height for hottest weather and water lawns and gardens in the early morning to reduce evaporation.

Don’t fertilize trees or shrubs, especially fruit trees, after mid-July, or you’ll encourage tender new growth that won’t harden off before winter.

Discourage mites by hosing dust from evergreens, leafy shrubs and hedges.

A strong spray of water also flushes aphids from plants.