Experts in weed eradication recognize five general strategies for controlling invasive plants. These are listed below, along with suggestions for applying these strategies in the home landscape. In addition, you will find specific suggestions explained in more detail in the “Control strategies” section of each Fact Sheet.
Preventive controls stop invasive plants before they can become established.
- Monitor your landscape frequently and regularly. Be diligent and persistent every year, month, and week. Seeds can lurk in the landscape for many years and germinate when you least expect.
- Be sure that any clothes, boots, gloves, and tools used in the landscape are free of mud and seeds.
- Be sure that pets don’t bring home any seeds in their fur or paws. If a motor vehicle is driven in an area with an invasive plant infestation, perhaps in the forest, be sure that tires are free of mud and seeds.
- Do not allow invasive plants to flower or go to seed! Get them before they spread.
Physical (or mechanical) controls kill plants directly or make the environment unsuitable for them.
Removing invasive plants by hand is not an easy job, but with persistence you will be successful over time. Continuing these techniques can prevent a reinfestation, too.
- Know the plant’s life cycle because it is useful for understanding how to control it.
- Annuals are easier to remove early in the season before their roots get established.
- Biennials are easier to remove in their first year of growth, when their rosettes are in their early stages of root development. In their second and final year, they flower, go to seed, and their roots are firmly established.
- Perennials live for many years and are extremely difficult to control when they are well established. Roots spread far, wide and deep, and can re-grow from small segments left behind in the soil. They can easily persist for many years, and each year their infestation expands to cover more and more territory.
- Remove invasive plants while they’re young, when the job will be easier especially in the spring when soils are moist.
- Remove plants by hand, by gently pulling up, and, if the root resists, by twisting. Try to remove the entire root system if possible.
- Use a clean, sharp hand tool or shovel to dig out invasives. You do not need to dig out the entire taproot. Cut the taproot a few inches below the soil, and check back frequently to be sure the plant has not re-grown. Try a hori hori knife!
- Be very careful to disturb the soil as little as possible. Seeds are more likely to germinate in loose soil, so try not to create a fresh new seed bed for next season's weed crop.
- Clip off perennial vines, like field bindweed, below the soil level so they can’t photosynthesize. Monitor continually for re-growth, and clip again. Repeat often. Digging out perennial vines disturbs the soil too much and encourages re-growth.
- If the plant has no flowers, buds, or seeds, pull or dig it out, and turn it upside down, leaving it on the ground to decompose and nourish the soil, or put it in a compost bin.
- Bag carefully and dispose of any plants that have buds, flowers, or seeds.
- Bag all roots of perennial invasives because they can re-root.
- Use thick mulch to prevent seeds from germinating or to smother seedlings. After weeds have been pulled, a thick layer of mulch can prevent their re-growth. You can get free compost from the City's compost program.
- If necessary, for larger populations, you can use a string trimmer before buds appear, and be sure to check periodically to be sure no plants have re-grown. It is possible to deplete a weed's capacity to grow by forcing it to re-grow constantly. However, this method is not recommended for perennial plants. It can stimulate growth considerably in the perennials’ well-developed root systems.
- For small areas, a thick layer of newspapers or cardboard can be used to smother a severe, dense infestation. This deprives the roots of sunlight, and overheats the plants, and they die. However, any native plants under the layers will also die. You can cover the newspapers or cardboard with mulch to improve the appearance.
- Consider solarizing the soil. This involves placing clear plastic on the soil and heating it with solar radiation to kill weeds. The University of California has an excellent website on soil solarization. See Solarization for Gardens and Landscapes.
Cultural controls promote the growth of desirable species.
They can reduce establishment, reproduction, dispersal, and survival of invasive plants over time.
- Remember from year to year where specific invasive species are located to help make future identifications easier and to spot infestations early. Maybe make a map. Monitor these locations frequently.
- Plant native plants or seeds, or put down a layer of mulch, where invasive species have been removed. Otherwise, invasive plants will find their way back into the bare spaces.
- Prevent new infestations by being sure that any clothes, boots, and gloves used in the landscape are free of mud and seeds. Be sure that pets don't bring home any seeds in their fur or paws. This is very important for annual weeds like cheatgrass and medusahead rye.
Biological control is the use of natural enemies—predators, parasites, pathogens, and competitors—to control pests and their damage.
Since these strategies involve using diseases or insects on very large populations or monocultures, they are generally not appropriate in home landscapes
Chemical control is the use of herbicides to disrupt unwanted plant growth.
It is preferable to avoid herbicides because they are harmful to the environment, including precious pollinators. However, they may be the best eradication method in certain situations.
- Consider several factors when choosing to use a chemical control, such as the target species, timing of application, and the number of applications required.
- Herbicides can be organic or synthetic chemicals.
- Always read the label carefully before using any herbicide and follow the manufacturer’s instructions exactly.
- Some chemicals require a pesticide applicator license for their use.
- Get expert advice - try Ada County Weed Control.
- Contact your local county extension office for more information on chemical control.