Managing Weeds Without Poisons

People often repeat Ralph W. Emerson’s maxim: “A weed is a plant whose virtues remain undiscovered.” And although I appreciate the virtues that many weeds have, I doubt many gardeners would accept that as the final say. Most of us have extensive experience with bindweed, thistle, goathead, ragweed, dandelion, and cheat grass - not to mention some aggressive natives like Whiplash Daisy, Wood’s Rose, Hairy Goldenaster, and herbs like mints, comfrey, and sweet grass. The main point for managing weeds without toxic chemicals seems to be: How do we keep certain plants under control?

Sixty years experience dealing with weeds doesn’t make me an expert, nor does 30 years as a nursery professional, but I will attempt to be helpful. To be honest and not too fatalistic, weeds are plants that are tremendously adaptable and successful; no amount of digging or toxic herbicides has been able to defeat them. In fact, as you may know, since that toxic “cure-all” Roundup has been the most popular herbicide, many weeds have become resistant to it, including 14 US species and up to 34 species worldwide.

The two ways that weeds (and other plants) spread are by seeds and roots. Sometimes seeding types can be controlled by mowing or removing seeds before they ripen. It doesn’t always work 100%, as with dandelions that can bloom after mowing below the level of the mower. Sometimes weeds that spread by roots can be controlled by repeated digging, not allowing green growth to photosynthesize, but digging can also help spread plants like comfrey and Snow-on-the-Mountain (Aegopodium).

In general it is important to find out what a weed likes—water, light, fertilizer—and restrict that. Water-loving weedy plants like Creeping Charlie (Lysimachia), vinca, ivy, and creeping buttercup (Ranunculus) all can be tamed with drier conditions. An important strategy in conserving water and managing aggressive plants is to group together plants with similar water needs. Another is to disturb the soil as little as possible so you don’t bring weed seeds up into the light to germinate. Weeds are often hardest to control in a new garden. The more a garden is planted, especially with tough groundcovers around taller perennials, and/or mulched, the easier it is to keep it weeded. The stronger the plants, the more they will outcompete weeds for light and nutrients.

One of the more interesting books on weeds is Katrina Blair’s The Wild Wisdom of Weeds. She spends a lot of time discussing the many values of weeds (with nutrient-dense recipes), especially 13 “essential plants for human survival.” Not just a dreamer, this Durango woman has an MS in holistic health education and a lot of practical experience. Her Turtle Lake Refuge organization provides greens for school lunches, has a wild foods café, and manages at least one park in Durango organically, along with several organic lawn care projects, classes, and field trips, locally and internationally. She has had positive results with a homeopathic weed ash remedy detailed in her book. (She sometimes teaches on the Front Range, including at Harlequins Gardens.)

Horticulturist Dr. Lee Reich has written Weedless Gardening. His experience-based approach includes feeding garden plants compost and nutrients from the top without digging, making paths to prevent compaction, using mulch and drip or focused irrigation. By not turning the soil, light deprived weed seeds don’t germinate. By pinpointing irrigation, watering doesn’t help weeds. And by supporting strong plants, weeds are much less of a problem.

Charles Walters, founder of ACRES USA, in his book, Weeds: Control Without Poisons, states that the major agricultural weeds “can be rolled back best with fertility management, not with herbicides.” And he is specific: calcium for quackgrass, manganese for thistles; reduce phosphorus for cocklebur. Ragweed decreases with greater porosity, air in the soil and more irrigation. Bindweed prospers in soil low in organic matter, calcium, and soil life. Dandelion prospers in low calcium, high phosphorus, and high nitrogen.

My personal approach for 30 years in my xeriscape garden is to use hand weeders: one with a sharp point, one broad and deep, and sometimes a narrow spade for the weed that got away. I start early in February or March digging out weed grasses that grow fast in cool weather and can soon bury a small perennial. If you wait too long, the perennial comes out with the weed. In April (or March) when the Bindweed is no more than 1"-2" tall, I hold the weed with my left bare hand while my right pushes a long bladed weeder under, swings and cuts the root. When I feel this, I pull out the hopefully 3"-4" long root and put it in my bucket. Small weeds I often just lay next to the plant for mulch, but Bindweed can re-root, and big weeds with seeds must be taken away. This slice and pull method does not turn the soil.

If I have cut the roots deep, the Bindweed is stressed since it has not photosynthesized for a few months. So maybe I won’t see a new top for two weeks. Before the weed is more than 2"-3", I dig again. This really stresses the Bindweed. By the time it is 2"-3" high again, my perennials and shrubs are bigger and leafing out which deprives the Bindweed of sunlight—another big stressor. I don’t start watering until May unless it is really dry, which gives an advantage to my established plants. Then I mulch where the ground is bare and later another round or two of weeding.

There are a number of non-toxic herbicides; most are vinegar or citrus-based with soap and maybe salt. We tested 5 kinds four years ago and only two proved really effective: straight 15-20% acetic acid vinegar and citrus-based Avenger. Both perform best in hot sunny weather on small weeds. Truthfully, I don’t see the point of spraying a big weed which when it dies is a black dead thing that has to be pulled. Why not pull or dig it in the first place? A broadleaf herbicide – IronX – is supposed to be non-toxic but I haven’t researched it enough to recommend. Mulch really helps with weeding because the weeds come out much more easily.

In lawns use corn gluten as an organic weed and feed. It prevents seeds from germinating and supplies 9% nitrogen. It is very effective even with dandelions if you apply it spring and fall every year. Weeding in lawns is also reduced by mowing 3" high so the plant is stronger. Aerate once a year (Sept. is best) followed by corn gluten or low-nitrogen fertilizer, then occasionally topdress with a fine compost.

Really bad weeds can be killed by solarizing the whole area with clear plastic or cutting off the light, water, and air with a sheet of pond liner. Weed barrier fabrics promise the moon but also deliver many problems: the pores plug up in a few years and prevent water and air penetration, tiny weed roots go through holes in the fabric and removing them makes a bigger hole; and often the mulch blows off and exposes the ugly fabric. Paper, newspaper and cardboard make a good weed barrier, covered with mulch and compost.

Weeds are here to stay. Toxic herbicides don’t solve the problem and they poison you, kids, pets, wildlife, and valuable soil life. If you discipline yourself to stay on top of weeds, and plant and mulch, the weed problem gets to be less and less.

Mikl Brawner and his wife Eve co-own Harlequins Gardens in Boulder, specializing in organic veggie starts and herbs, natives, sustainable roses, xeriscape, unusual perennials, and products to build healthy soil.