Weeds as Companion Plants

Spring 2001

By Sue Smith-Heavenrich

Certain plants, when grown in combination, enhance each other’s growth, repel insects, and increase fruit production. Called “companion planting,” the idea has always intrigued me. So every spring I carefully map out a garden plan complete with successive plantings and companion plants neatly pencilled in. Along with my usual beans and greens, I order packets of seeds for plants with long Latin names I can barely pronounce. By July my garden bears no resemblance to those carefully drafted plans neatly tucked into my garden notebook and languishing beneath a pile of stuff accumulating on the hutch.

By July, my garden is wild. Black-eyed Susan and ox-eye daisies bloom between the rows of garlic. Milkweed and lamb’s quarters have formed solid partnerships with the beans and corn. Smartweed threatens to smother the onions. I reach for the hoe and – put it back down. If the point of companion planting is to increase diversity by providing habitat for beneficial insects, which, in turn, will munch on potato beetles and aphids – then I have accomplished it. What look like weeds may actually be wild companion plants, I tell myself.

For years, Dr. Miguel Altieri has been studying the ecological role of weeds in agricultural systems. “Agroecology” he calls it, and he cites many examples of cropping systems in which the presence of weeds enhanced the biological control of pests. While studying beans in Columbia, he noticed that as the density of weeds increased, the density of the major bean pest (a leafhopper) decreased. In other trials he showed that beans grown with pigweed had lower populations of bean beetles than beans grown in monocultures. Weedy undergrowth in apple orchards contributed to higher populations of parasitic wasps, which, in turn, helped control apple fruit pests. The understory of ragweed, goldenrod, smartweed and lamb’s quarters in a New Jersey peach orchard contributed to the decreased population of the oriental fruit moth.

Certain weeds contain chemicals that repel insects. Mustards, for example, contain potent sulfur compounds, and goldenrod leaves are toxic to many six-legged critters. Other weeds are important because they provide nectar or shelter to small parasitic wasps. Queen Anne’s Lace and other umbels are well known habitat plants. Composites, too, attract beneficials. Black-eyed Susan and ox-eye daisies attract paper wasps, which hunt hornworms and Colorado potato beetle larvae. Goldenrod supports over 75 species of insects, mostly beneficial, and pigweed supports no fewer than thirty.

Altieri suggests letting weedy strips grow every 10 rows or so in agricultural fields. Gardeners with little room to waste can allow weeds to grow in ditches or along garden edges instead. Dandelions, lamb’s quarters, goldenrod and evening primrose are on his list of weedy “good guys.”

Ray Allen, founder and owner of American Meadows and The Vermont Wildflower Farm, has these words of caution for those who would invite weeds into their gardens: Know Thy Plants!

Some weeds, like Queen Anne’s Lace, are biennials. This means that they don’t form huge root masses, as they live only for a couple of years. Others, like Jerusalem Artichoke or goldenrod, are beautiful wildflowers that will indeed attract many beneficials to the garden, but they form large, tough root mats that grow larger each year. Allen suggests that gardeners stick with wild annuals and biennials for the garden. Leave the perennials on the perimeter, where you can mow them if necessary. Ironically, his list of “plants to absolutely avoid” includes some of my favorite wild guests: yarrow, ox-eye daisies, goldenrod and clovers.

Before allowing wild companions to take root, gardeners need to consider some trait in addition to invasiveness and tenacity. One is competition for water and nutrients. Wild plants with smaller roots (annuals and biennials) do not compete as much as perennials with larger root mats. On the other hand, in a dry year you can sacrifice the wildflowers, turning their greenery into water-conserving mulch with the flick of a hoe-blade.

When using wild plants for companions, consider whether they are allelopathic to the crops growing nearby. “Allelopathy” is the suppression of the growth of one plant by another. Goldenrods have some slight effect, and sunflowers are thought to be allelopathic – although that might be due to their seed hulls lying on the ground. One weed that is known to be allelopathic is quackgrass. It has been shown to reduce yields, inhibit seed germination, and reduce growth of peas, beans, oats, barley and flax.

Some weeds harbor fungal diseases that you’d rather keep out of your garden. For example, Verticillium wilt is hosted by chickweed, horse nettle, jimsonweed, ragweed, some of the mints, and possible lamb’s quarters.

I like having wild garden companions. They don’t require coddling, they bring color into the garden, and they’re ideally suited to the environment. Furthermore, they’re cheap. And if I get tired of them, I can always – weed ‘em!

A List of Wild Garden Companions:

Aster (Aster sp.), perennial. These composites are usually violet, with many thin petals and a yellow center, but can also be pink, white or blue. They grow from 1 to 3 feet tall and bloom in the fall. If grown in a garden, they can be pinched back like mums to be kept shorter.

Black-eyed Susan (Rudbeckia hirta), biennial. This member of the sunflower family has a single, slender-stemmed blossom with a chocolate center disk and numerous long yellow rays. It grows up to 3 feet tall, and blooms from June through October. American Indians used it medicinally.

Chicory (Cichorium intybus), biennial. This alien can be found along almost any roadside. The blue stalkless flowers measure almost 1-1/2 inches across with petals that are square-tipped and fringed. The plant has basal leaves, like a dandelion, and can grow up to 4 feet tall. It blooms from June through October. Chicory can be tossed into salad or cooked, and the root is often roasted and ground to make a coffee-like drink.

Clovers, perennial. These plants are in the legume family, so they can fix nitrogen. They are edible, have been used in medicines, and supposedly contain a number of chemicals, including estrogens.

Coltsfoot (Tussilago farfara), perennial. This dandelion-like flower appears early in the spring. Later the horseshoe shaped leaves emerge. It grows 6″ to 18″ tall, and the stem is reddish.

Cornflower or Bachelor’s Button (Centaurea cyanus), annual. This garden escapee is usually blue, but also can be pink and white. It grows up to 2 feet tall, and flowers from July to September. It reseeds itself – a decided advantage for the lazy gardener who wants flowers with no work.

Dandelion (Taraxacum officinale). This well-known composite blooms in the spring. Not only does it attract a host of beneficials, but it is edible. An obvious problem is seed production. We have addressed this with selective weeding: allowing the seedlings to grow only in certain areas.

Fleabanes (Erigeron sp.), perennial. These composites are slender with pink to violet flowers that measure less than an inch across. The flowers have numerous (sometimes up to 150) thin rays. One species was used to treat fevers and bronchitis. They bloom in June and July.

Goldenrod (Solidago sp.), perennial. There are many kinds of goldenrod, some plume-like, others flat-topped, and others club-like, but all with golden flowers. Usually they grow 3 feet tall. They bloom from August through October. Some species have been used in medicines by American Indians to treat burns, snakebite, fevers.

Lamb’s Quarters (Chenopodium album), annual. This branching weed often has mealy, red-streaked stems. The leaves are diamond-shaped and broadly-toothed, often white beneath. It grows up to 3 feet tall and blooms from June to October. The greens may be cooked, and seeds ground into flour. American Indians ate the leaves to treat stomach aches and to prevent scurvy.

Milkweeds (Asclepias sp.), perennial. The common milkweed is a stout, downy plant with droopy pink flower clusters. It stands about 3 to 5 feet tall and blooms from June to August. The stems and leaves exude thick, milky sap when broken. This sap can irritate the skin, so if you’re handling milkweed, wear gloves and wash your hands afterwards. The pods and other parts are edible, and American Indians used the plant for medicines.

Mints. There are many kinds of wild mints. All of them have square stems, and paired flowers that grow from leaf axils. Most of the flowers are pink, blue or violet and bloom from June through September. Most are perennial. Some of the wild mints that are beneficial are:

American Pennyroyal (Hedeoma pulegioides)

Gill-over-the-Ground (Glechoma hederacea)

Heal-all (Prunella vulgaris)

Mullein (Verbascum thapsus), biennial. This tall plant (it grows up to 6 feet) is in the snapdragon family. The plant has a thick, hairy stalk topped by a club of yellow flowers. It blooms from June through September. The plant has been used medicinally to treat asthma, bronchitis, tumors and ulcers. According to one reference (A Field Guide to Medicinal Plants for Eastern and Central North America, by Steven Foster and James A. Duke, Houghton Mifflin, 1990), mullein leaves contain rotenone and the hairs may irritate your skin, but it’s a striking plant to have in the garden.

Mustards (Brassica sp.), annual. The yellow and white flowers of these plants have four petals. Many are edible, and some have medicinal uses.

Ox-Eye Daisy (Chrysanthemum leucanthemum), biennial. This is a white daisy with yellow center disk that blooms from June through August. The leaves are edible, if you collect them when they’re young and tender.

Purple Coneflower (Echinacea purpurea), perennial. This favorite medicinal plant has pink Black-eyed Susan-like flowers. It is a slow grower and a slow spreader, and is very hardy.

Queen Ann’s Lace (Daucus carota), biennial. This is a wild carrot, in the umbelliferae family. It is an alien species that has naturalized, but unlike purple loosestrife, it is not invasive. The flat clusters of flowers form a lacy pattern. It grows 2 to 3 feet tall, flowers from May to October, and is usually found along roadsides and in fields. The roots have been used medicinally in a tea, and some scientific studies confirm that it has bactericidal properties.

Sunflower (Helianthus sp.), annual. The traditional sunflower has a large brown center with yellow rays. It’s a tall plant, often growing 5 or more feet in height. There are many garden varieties in a palette of colors.

Tansy (Tanacetum vulgare). This plant grows up to 3 feet tall, topped by showy flat-topped clusters of golden, button-like flowers. The leaves are fern-like and contain insecticidal compounds. It blooms from July to September.

Tickseed (Coreopsis sp.). These yellow flowers are in the composite family. Most have eight rays, each tipped with 3 to 4 teeth, and thin, lance-shaped leaves. They grow 1 to 2 feet tall, and bloom from June to August.

Toadflax (Linaria vulgaris). This member of the snapdragon family is also known as “butter-and-eggs.” It grows from 1 to 3 feet tall, with spikes of yellow to orange snapdragon-like flowers, and blooms from June to October.

Wild Lettuces (Lactuca sp.). These are tall, branched plants with dandelion-like flowers. They bloom from July to October. Like dandelions, they produce many wind-blown seeds.

Wild Sweet William (Dianthus barbatus), biennial. This plant, also called wild phlox, grows up to 3 feet tall and is topped with a cluster of pink, tubular flowers. The wild variety has purple spots on its stem, and opposite leaves.

Wormwood (Artemisia absinthium), perennial. The leaves of this plant are deeply cut and white and silky on both sides. Tiny yellow-green flowers grow in drooping clusters. It blooms from July to September.

Yarrow (Achillea millefolium), perennial. This tall plant (up to 3 feet) has soft, feathery, fern-like leaves and tight, flat flower clusters, usually white. Though it has been used in medicinal teas, it contains some toxic chemicals. It blooms from June through August.


Just in case you don’t have weeds in your garden, or you do but they’re not the right kind – you can order seeds of flowering wild annuals and perennials:

American Meadows (www.AmericanMeadows.com) not only has seeds, but also a 70-species wildflower encyclopedia with photos, botanical information, how-to-grow, etc.

Companion Plants, 7247 N. Coolville Ridge Rd, Athens, OH 45701. www.companionplants.com/

Fedco Seeds, PO Box 520, Waterville, ME 04903-0520. (207) 873-7333; www.fedcoseeds.com/ Every year Fedco offers a wildflower blend of perennial and self-sowing annual plants that are native or naturalized to the Northeast. The species include many of the wildflowers listed above.

Johnny’s Selected Seeds, Foss Hill Rd, 955 Benton Avenue Winslow, ME 04901; 1-877-564-6697; www.johnnyseeds.com/. This year Johnny’s is offering a special collection of seeds called “beneficial borders,” flowers that attract beneficial insects.

About the author: Sue Smith-Heavenrich writes, raises her children, gardens and tutors math in Candor, New York. She is currently taking Cooperative Extension’s Master Gardener course, as well as karate lessons.

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