Organic gardening and lawn-care practices nurture plants and control diseases and pests in ways that are natural, allowing you to avoid the use of synthetic chemicals and unnatural manipulation. But organic weed control is much more than just killing weeds safely. It is first about growing a healthy lawn to minimize weed pressure. It should also involve an integrated pest management (IPM) program that allows for an acceptable amount of weeds (weed threshold) in exchange for a safer, non-chemical environment. IPM is an ecosystem-based strategy that focuses on long-term prevention of pests or their damage through a combination of techniques such as biological control, habitat manipulation, modification of cultural practices, and use of resistant varieties. Pests aren't just problematic insects but also weeds that compete for resources. Under IPM standards, eradication of weeds by chemical means is the last resort.
Promoting a Healthy Lawn
The basic principle behind organic weed control is that healthy soil and grass promote vigorous plant growth that out-competes the weeds. Therefore, the first step of organic weed control is to test the soil to learn about any deficiencies, then naturally amend and fertilize the soil according to the soil test results. A soil test will determine the pH, which should range from 5.8 to 7.2 for lawns. Warm-season grasses tolerate slightly lower pH, which cool season grasses prefer a higher pH. From there, follow best practices to keep the lawn as healthy and robust as possible:
- Mow at the highest level possible to encourage a dense lush lawn capable of crowding out of weeds.
- Reduce compaction by aerating. Most experts recommend aerating once each year, in the fall.
- Improve water and nutrient uptake by de-thatching, but only when it is necessary. De-thatching is an aggressive action that can damage grass plants. It is necessary only when thatch has become so dense that it prevents water and nutrients from penetrating into the soil.
- Topdress the lawn with compost. This is a simple matter of spreading a light layer of organic and well-decomposed compost onto the lawn and raking it in.
- Re-seed bare patches in the fall, well before frost. This gives the grass seed a head start for spring so the patches fill in with grass and aren't left open to weed seeds.
- Avoid scalping the lawn (cutting it too short) when mowing. Damaged grass crowns recover very slowly and give weeds an opportunity to establish.
- Water deeply and infrequently. Maintain adequate soil moisture, but do not over-water. Many weeds have superficial roots and are aided by frequent watering.
Organic Weed Control Methods
While maintaining a healthy lawn is the best way to minimize weed growth, often direct weed control is necessary in local areas or to deal with concentrated weed growth. There are several options for eliminating weeds organically:
Herbicidal soaps are natural products for controlling mosses and algae. There are numerous weed-killing formulations using natural oils, concentrates, and other organic substances. These are all non-selective herbicides; in fact, there are no organic herbicides yet available that are selective and kill only broadleaf weeds without affecting turf grasses and garden plants, as many chemical weed killers do.
Manual weed removal with weed puller tools, long screwdrivers, hand trowels, or bare hands is the safest and most effective method for eliminating weeds. A variety of "weed-popper" tools make this work easy and offer the added benefit of providing lawn aeration. In a garden, systematic weed pulling will gradually result in a garden that is easy to care for, since weeds are no longer present to go to seed.
Weed flamers are gaining popularity for organic weed control. They are essentially modified propane torches used to burn problem weeds. A single application of heat from a propane flame kills almost any weed, but it also kills grass, so this method is best for areas where desirable grass is not at risk.
Dayan, Franck E., and Stephen O. Duke. "Natural Products For Weed Management In Organic Farming In The USA". Outlooks On Pest Management, vol 21, no. 4, 2010, pp. 156-160. Research Information Ltd., doi:10.1564/21aug02
Taylor, Erin C. et al. "Organic Weed Management In Field Crops With A Propane Flamer And Rotary Hoe". Weed Technology, vol 26, no. 4, 2012, pp. 793-799. Cambridge University Press (CUP), doi:10.1614/wt-d-12-00035.1