- Weeds in Gravel Driveways
- Vinegar for Weed Control
- Renovating a Weedy Lawn Without Pesticides
- Invasive or Noxious Weeds
- Moss in Lawns
- Moss on Roofs, Decks, and Sidewalks
- Mulching for Weed Control
Weeds in gravel driveways can be pulled by hand or seared with flame weeders, which are propane torches designed to kill weeds. Available brands include Weed Dragon and Weed Wizard, and generic products are widely available at hardware stores. Flame weeders are especially effective against annual weeds; for perennial weeds, multiple treatments are usually necessary. They are best used when weeds are small, and before they set seed. It’s important not to flame weeds when they are dry and may catch fire.
To use a flame weeder, move the flame back and forth, searing weeds but not burning them. Do not use on bark mulch, plastic, or near flammable debris or dry plants. Keep flame away from feet, hands, or clothing, and move backwards as you work to avoid walking over hot surfaces. Keep a fire extinguisher or water supply handy.
If it is impractical to pull weeds manually or to sear them with a flame weeder, less-toxic herbicides can be used. Various products are available and can include acetic acid (vinegar), eugenol (clove oil), or fatty acids as active ingredients. These products only damage portions of plants that they directly contact, and also do not distinguish between broad-leafed weeds, grass, and ornamental plants. They are most effective for killing annual weeds, and repeated applications may be necessary for perennial weeds. If you choose to use a less-toxic herbicide, be sure to read and follow label directions, and to store it in a safe place away from children and pets.
Some people have found vinegar to be an effective non-selective, contact herbicide (weed killer). In fact, some commercial herbicide products are available that contain acetic acid (vinegar) as an active ingredient. In the ready-to-use formulations, the concentration of acetic acid in these products is about the same as in regular household vinegar. Advantages of using household vinegar are its low price and the fact that it doesn’t contain undisclosed “inert” ingredients. However, straight vinegar is less effective than the commercial products because the commercial products contain a surfactant that allows the products to wet the leaves better. Another disadvantage is that vinegar doesn’t come with an EPA-approved label with directions and safety information.
We generally don’t encourage people to concoct home-made pesticides, but don’t have any problems with people trying vinegar as a less-toxic weed killer. Bear in mind that being non-selective, vinegar may kill desirable plants such as grass or ornamentals. Vinegar also only affects parts of plants that come into direct contact with it, so spraying it on leaves or stems won’t affect the roots unless some of it happens to trickle down to the soil, and even then there’s no guarantee that roots will be affected.
For more information on less-toxic herbicides, please see our FastFacts: Weeds in Gravel Driveways (at the top of this page).
In the maritime Northwest, spring (April to mid-May) or fall (mid-September to mid-October) are the best times to renovate. Lawn renovation involves the following steps: aerating to reduce soil compaction and improve water infiltration, overseeding to thicken turf and fill in bare spots where weeds may take hold, topdressing with compost to add nutrients, support soil life, and improve drainage, and for lawns that have accumulated more than 1/2 inch of thatch, de-thatching.
The use of herbicides is not necessary in lawn renovation, though it may be useful in cases where weed cover is extensive. In such cases, repeated spot treatments with less-toxic herbicides prior to starting the above steps may be helpful. Physical removal of weeds with long tap roots (such as dandelions) will also be beneficial; long handled pincer-type tools are available for this purpose. In cases where weeds make up over 50% of a lawn and soil is very poor, complete removal and replacement may be warranted.
For more detailed instructions on lawn renovation and removal, please see:
Bear in mind that the best way to keep weeds out of your lawn is to grow thick, healthy turf.
As with other weeds, invasive or noxious weeds should be controlled manually if possible. Techniques include pulling, cutting, mowing, cultivating, digging, and grubbing. The most effective techniques vary depending on the type of weed, so it is important to identify the weed and obtain specific instructions. It is especially important to find out whether or not the invasive weed you are planning to control is a noxious weed. Noxious weeds are invasive weeds that are considered to be especially problematic, and control requirements are set by noxious weed control boards. In Washington, Class A noxious weeds must be controlled throughout the state, but requirements for Class B and C weeds vary among counties. The best sources for information on noxious weed identification and control are your county and state noxious weed control boards:
Other sites for information on invasive weeds:
In some cases, physical controls may be impractical or ineffective, and temporary use of herbicides may be warranted. If possible, they should be injected directly into stems, or wiped onto cut stems (be sure to check what methods are appropriate for your weed and the product chosen). These methods decrease the amount of herbicide used as well as the amount dispersed into the environment, and are preferred over spray applications. Goats, available for rental, can also be helpful in some cases.
Also, when choosing plants for your garden, make sure not to plant invasive or noxious weeds such as English Ivy that are still available at nurseries.
Although often considered a weed, moss is actually a native plant. If moss thrives in your lawn, it means that conditions favor moss over turf. If you don’t address those conditions, your efforts at moss control will be temporary at best. Moss does well in shady, moist soil with a slightly acid pH. Grass likes sun, soil that dries out between waterings, and alkaline pH. You can help your grass outcompete moss by pruning trees to let in more light, solving drainage problems, and liming the soil. Consider replacing grass with other groundcovers or plantings in deep shade, on slopes, or in boggy areas.
Once the conditions above have been corrected, moss can be raked out fairly easily and the area overseeded to thicken the turf. With this approach, chemical controls may not be needed at all.
Chemical controls for moss include iron sulfate and moss-killing soaps. Soap-based products are rapidly biodegradable and relatively non-toxic. Always use any pesticide according to label directions. Iron sulfate is fairly benign, but avoid products corrosive to eyes, identified with the word “Danger” on the label. Also, be aware that iron will stain sidewalks.
Moss or algae form on roofs, decks, sidewalks, and other hard surfaces that are located in shady areas. They can damage roofing materials and cause water leakage, make sidewalks and decks dangerously slippery, and cause staining.
Moss can be removed from decks and sidewalks by scraping or by pressure washing. The latter approach is not advised for roofs because it can damage or get under shingles. A leaf blower can be used to remove moss from roofs during the dry season. Once heavy buildup has been removed, chemical moss killers can get the rest and provide some residual protection.
Moss-killing soaps, such as Safer™ brand, are among the least-toxic options. They also have the advantage that because they are soaps they also clean very effectively. Zinc and copper-based products are potentially a risk to aquatic organisms and should not be used if roof runoff has a direct path to a lake, stream, or storm drain. Some zinc and copper products are formulated with solvents that are toxic to inhale.
A mulch is a layer of organic material that is placed on the soil surface around plants to add nutrients, retain moisture, reduce runoff and soil erosion, and prevent weeds. Around annuals and vegetables, apply 1-3” of leaves, compost, or glass clippings. Around trees, shrubs, and woody perennials, apply 2-4” of woody mulches like wood chips or bark. If you have a choice between wood chips and bark, wood chips are preferred because bark contains waxes that prevent absorption and release of water, is sometimes contaminated with weeds or salt, and softwood bark (such as from Douglas fir) contains sharp fibers that can be painful to work with. Mulches should be spread around plants to the drip line (the diameter of plants’ outermost branches) or can cover an entire garden bed. It’s important to keep mulch a few inches away from the trunks of trees and shrubs.
Though mulch can prevent the germination of weed seeds smothered below it, do note that some types of mulch, such as hay and bark, can be contaminated with weed seeds. (Straw and wood chips are less likely to be contaminated.) Weed seeds can also blow in on top of mulch after it is applied and germinate; however, weeds are usually easier to pull from mulch than from soil.
Mulch can be applied at any time, but early spring, before soil moisture has evaporated, is an especially good time. It’s a good idea to weed the area before applying. Lawns can also be ‘mulched’ by leaving behind clippings when mowing; mulching mowers that blow clippings back into the ground are available. Compost is also an excellent soil amendment for turf.
For more information on mulch, see the King County fact sheet Make the Mulch of It (288kb PDF file).