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3. Tools & Techniques: Chemical-free Weed Controls
by Beth Hanson
Nature has ingeniously designed plants and animals to spread their genes as far and wide as possible—and some are better at this than others. For gardeners this means constantly having to decide which plants we can live with and which ones have to go. Techniques to rid the garden of the unwanted range from benign "mechanical" methods to the riskier chemical controls. If a non-chemical method will work for you, use it. You don't want to unnecessarily expose desirable plants to herbicides that may be just as poisonous to them as to the weeds. Unless an infestation of invasives is so severe, or your property so extensive that mechanical controls are impractical (as on many public and park lands), you may well be able to banish the weeds using one of the following non-chemical techniques.
Hand-pulling
Pulling weeds by hand, probably the most ancient weed removal technique, works best with smaller annual and biennial plants before they have had a chance to produce and spread their seed, especially when the soil is damp. If possible, pull up the entire root system of the plant, but try not to disturb the surrounding soil as this will invite further invasion. If you do disturb the soil, replace the litter on top of it, leaving the area looking as much as possible as it did when you arrived. Take care not to trample native plants or to compact the soil; this may be easier if you sit on an inner tube while weeding to distribute your weight more evenly.
Weeding Tools
Two small companies in the West now produce tools designed specifically for pulling shrubs such as Scotch broom, tamarisk, thistle, honeysuckle, holly and Russian olive. The Weed Wrench and the Root Jack are both basically lever arms with a pincher or clamp at the bottom to grip the stem of the plant. Once the stem is caught in the grip, the user leans back, tightening the clamp in the process, and after a little rocking, the entire plant comes up, roots included. If the soil is wet, put a board under the corner of the arm so it does not sink into the ground. (The Weed Wrench is available from New Tribe, 541-476-9492, the Root Jack from Mike Giacomini, 415-454-0849.)
Cane Knife
Sugar-cane cutters use these knives to cut through thick cane stems. They're similar to machetes but have a deeper blade (use them with care!) and a hook on the back to pick up what's just been cut. Cane knives work well on large herbaceous plants such as nettle, lantana, mullein, blackberry and bolted second-year thistle, as well as young trees and shrubs. With practice, you'll be able to cut through a 1- to 2-inch thick stem. Cane knives can be hard to obtain in the cooler regions of the continent. If you have trouble finding one, a machete will work almost as well.
Three-pronged Claw
This common tool is useful for pulling out vines such as vinca, English ivy and other plants that have lots of shallow roots. Cut into the patch of vines with clippers, then drag out the vine with this claw. When you're done, rake the soil back into place. Clearing an area with a claw can require a lot of work, but less so than hand-pulling in many cases.
Girdling
By cutting and pulling a 2-inch wide strip of bark away from the circumference of a tree trunk, you stop the flow of sugars through its cambium, and the tree will eventually die. The cut should be deep enough that you've cut through the thin oniony layer under the bark around the trunk, the cambium. Girdling works on many types of trees such as pines, some species of oak and maples. Most shrubs have so many stems that this method is impractical. A good knife with a blunt blade is the best tool for this job. Some gardening supply catalogs sell girdling knives.
Mulching
Many seeds need light to germinate and become established. If you cover the ground with a layer of non-living material (hay, straw, grass clippings, wood chips, plastic film), you will deprive the seeds of light, and thereby prevent unwanted seedlings from surviving.
Mowing
Some weeds can be controlled by mowing. Annuals are especially susceptible if mown shortly before they set flower, since by that time they have already used most of their root reserves to produce the buds. Mowing works best in meadows and grasslands. In woody areas you achieve the same effect using a weed whip (you can also mow more precisely), but be careful not to inadvertently girdle nearby trees. In backyards, it's almost always possible to kill weeds without herbicides if you are persistent and willing to mow at short enough intervals to exhaust the energy in the weeds' roots.
Heat
Hot water:
In urban and home situations, try pouring boiling water on the weeds that sprout between cracks in walks and drives. Deeply rooted plants are likely to come back unless the hot water reaches the roots. At schools and other public places where herbicides are out of the question, steam injectors are used to kill weeds.
Propane:
This method basically roasts seedlings but you need to get them when they are most susceptible—before they develop extensive roots.
Prescribed burning:
This method is most appropriate for large plots of land such as prairies and meadows, to kill those plants that won't come back after their foliage has been destroyed by fire (juniper or red cedar, Juniperis virginiana, for example, is a common invader of grasslands). Prescribed burns should only be conducted by a properly trained and certified burn crew. Contact your local extension agent if you think this control is appropriate for your situation.
Tilling
For those with large areas hopelessly infested with invasives, plowing the soil can be effective. By using the right type of plow to turn the soil in your area, you can cut the plants' roots and tip them upside down beneath a cover of soil, in effect smothering them. Tilling is comparable to digging out invasives—and whatever natives remain in the area as well—on a huge scale.
Beth Hanson is the former managing editor of BBG's 21st-Century Gardening Series.