Lawns: Weed Problems?

Many so-called “weeds” are beneficial to the lawn ecosystem and weeds are tolerated in an organic lawn to varying degrees. It wasn’t until the advent of selective herbicides that a lawn consisted of only grasses. Before that, any plant that lived under the mower blade was considered “lawn.”  This diversity of species led to lawns which were more tolerant of adverse conditions.

Often, excess weeds are a symptom of poor soil, a flag that lets you know a pH adjustment is needed or that an important mineral or nutrient is lacking. Correcting the soil pH ultimately controls weeds, as healthy turf and weeds cannot co-exist. The turf will shade and crowd out the weed.

In some cases, weeds can get out of hand and take over sections of lawn. If weeds need to be controlled, there are several organic products on the market approved for use. Corn gluten meal acts as a pre-emergent weed control that suppresses the establishment of plant seeds. It is applied in the spring between Forsythia and Lilac bloom, before weeds such as crabgrass emerge. It can be reapplied in early summer to prevent germination of late-season weed seeds.

Because corn gluten meal is high in protein, it contains approximately 10 percent organic nitrogen. This nitrogen level needs to be accounted for in the overall lawn management program, so that nitrogen is not over-applied during the season through additional fertilizer and compost applications, for example. The bare spots in the lawn where crabgrass was last year, treated with corn gluten, can be planted with an annual rye grass to “hold the spot” until a perennial lawn seed mixture can be established in the fall. Seed applied after corn gluten should be mixed with compost and the compost spread at least ½ inch thick in the bare areas.

Corn gluten meal is also effective in weedy flower beds, if applied before the weeds appear. Dust the meal on the bed as if it were salt and pepper hitting the dinner plate. (It doesn’t matter if the corn gluten contacts foliage. It only has pre-emergent properties, not post-emergent.) During the first season of use, apply the corn gluten meal again to the bed in the fall once the weeds have died back for winter.

Unwanted weeds that exist in the lawn or border, such as plantain or dandelions, can be organically controlled with the use of non-selective herbicides made from the essences of vinegar and lemon juice (ethanoic and acetic acids) or potassium salts. The weeds are cautiously spot sprayed, being careful to avoid any unnecessary over-spray or drift onto desirable lawn or plants. Two good products for this purpose are Burn Out™ and Scythe™. Always read the label directions carefully before use. Areas that are sprayed should be seeded immediately with compost, as above.  Dandelions can also be physically removed with a two pronged metal hand tool which digs up the tap root.

By Priscilla Williams and Mike Nadeau, Organic Land Care Committee