Regional Gardening Reports :: National Gardening Association

In the Garden:
Pacific Northwest
November, 2007
Regional Report

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Dandelion flowers can turn to seed overnight. Each of the seeds has its own parachute and can travel on the wind up to 2 miles from the plant.

Rooting Out Perennial Weeds

For years I have brooded about weeds. I've tried everything to eliminate them. I've smothered them with landscape fabric, spent hours pulling them out of my garden beds, doused them with hot water, and even anointed them with vinegar and oil. And still they come back.

Like our treasured ornamental plants, weeds can be perennial, biennial, or annual. Perennial weeds pose the toughest challenge because of their extensive root systems and their ability to spread rapidly. Standing in my garden, I can almost feel the roots expanding beneath the soil. I don't expect I'll ever get ahead of perennial weeds and yet I'm not about to give up in exasperation. Instead, I strive to keep perennial weeds at a tolerable level by a combination of prevention and control.

Getting to the Root of the Problem
If you know what types of roots your weeds have, you'll have a better idea of how to control them. If you're not sure, dig them up and see. Perennial roots can take the form of elongated underground stems (rhizomes or rootstocks); basal branches, which root at the nodes (running or creeping); deep, vertical taproots; bulbs and tubers; or fibrous roots.

In general, the best way to control perennial weeds with taproots, bulbs, and fibrous roots is to pull the weeds up while they're young, before their root systems become more extensive. To do this, of course, you must learn to recognize weeds and young sprouts. If you can't identify a weed, consult Weeds of the West (Western Society of Weed Science in cooperation with the Western United States Land Grant Universities Cooperative Extension Service, 1997) or Common Weeds of the U.S. (United States Department of Agriculture, 1971). Both of these books are excellent resources.

Pull Up Fibrous Roots
Plantain (Plantago major), with its relatively shallow fibrous roots, is an easy perennial to pull before its vertical spike of flowers goes to seed. The narrow-leaved plantain (Plantago lanceolata) also has fibrous roots and can be pulled up like its broad-leaved relative. Another common weed with fibrous roots is ground ivy. Both plantain and ground ivy grow in damp soils, making their removal that much easier.

Dig Deep
Old-fashioned violets, wild onion, and wild garlic are all perennial weeds that multiply by means of many small bulblets. The best way to eradicate them is by digging them out. Dig down deep after a good rain when the soil is loose, and get your trowel or spade completely underneath the bulbs. If you miss the bulb and only pull out the green stalks, you've wasted your time because the remaining bulbs will regenerate.

When you dig up the bulbs, throw away the entire ball of soil, which can be as large as your fist. Don't shake off the soil as you would with other weeds, because the bulblets may come loose and regenerate where they fall.

Dig Early
Unless you're cultivating dandelions for summer salads, you'll probably want to be rid of them. You'll want to get rid of curly dock, too, since one plant can generate 30,000 seeds in a single season. Dandelion, like curly dock and pokeweed, has long taproots, which should be dug out when you first notice the weeds. Large pieces of the taproot left in the soil are likely to sprout.

As with other deep-rooted weeds, wait until after a good rain, then use a narrow-bladed shovel or trowel to excavate around the root until you can get underneath it. Don't pop it up until you're sure you've found the entire root.

Pry up Rhizomes
Many perennial weeds have modified underground stems that can regenerate from small portions left in the ground. Those that spread from rhizomes are the most tenacious. Many of these weeds, such as white clover, bindweed, stinging nettle, and sheep sorrel, are the most troublesome weeds because they also creep along the surface.

You can stay ahead of them in small patches by diligent hand-weeding. To rid them from large areas, however, you may need to resort to using a low-toxicity herbicide.

Preventing Weeds
If you don't want to spray and you're tired of digging, you can try instead to prevent weeds from infiltrating your beds. A combination of landscape fabric, mulch, and a deep edge around a bed can protect the bed from perennial weeds with creeping runners.

Landscape fabric, which is laid over the soil to smother weeds while at the same time allowing for sufficient rain and air flow, is useful in a permanent planting, such as a shrub border. It is not practical for plantings of annuals or perennials where the planting pattern is irregular and the plants are replaced seasonally.

Mulching to a depth of 2 to 4 inches will slow weeds down and render the ones that do come through spindly enough to pull up easily. Be sure to keep the mulch away from the crowns of perennials since it can smother them or hold enough moisture to cause rot. Keep mulch away from tree trunks, too, so it doesn't provide a home for chewing rodents.

A 4- to 6-inch-deep edge bordering the bed will both slow creeping weeds and give the bed a pleasing line in relation to the lawn. You can also install a rigid edging, which will help keep the mulch in place. But don't let down your guard -- weeds will eventually reseed and creep over any edge.

Vigilance Has its Rewards
Weeds can be the best excuse to get out into the garden. They remind us that Eden requires constant cultivation. Instead of reaching for a chemical to poison a small patch of weeds, take a half hour to dig them out while you're listening to the birds and smelling the fragrances of the garden.

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