Weeds

Lawn, Garden and Roadside Weeds

By Jeannette Adams, Marilyn Dudek and Teresa Lopata

Introduction A definition of a weed is any plant growing in abundant quantities where it is not wanted. It interferes negatively with the growth of desirable plants, is persistent and difficult to eradicate.
Weeds are divided into perennial, annual, winter annual and biennial categories. Depending on the level of infestation, governing bodies have developed classifications and noxious weed control laws. These may differ from region to region. In Manitoba a listing of noxious weeds and a Tier Level categorizing the severity of infestation can be found on the Government of Manitoba Agriculture website.
For the purpose of this listing of weeds, we have chosen those weeds that are most commonly found on or near public and private gardens. We have also included a listing of plants that are still sold or exchanged as ornamentals, but can be very aggressive and spread easily into neighbouring properties.
Identification Identifying the “weed” can be difficult because many are very similar in appearance. Also identification depends on what stage of growth you are dealing with. It is important to examine leaves, stems and roots at the early stages of growth. As the plant matures you will have flowers and maybe seed pods to examine. Also consider where the plant is most plentiful, is it in sun or shade, dry or moist soil, tilled or compacted soil. Identifying the plant provides the information required to decide the best control methods.
Control Methods Early detection and removal of unwanted plants is the first line of defence. Making sure your desired plants are healthy and vigorous will impede the growth of weeds. Using mulches inhibits the growth of some weeds. Tilling and hand weeding removes most annual weeds. However, some weeds are very persistent and require repeated digging and discarding of all plant parts. If dealing with a large area, smothering or solarizing can be used. This is where dark sheeting, heavy cardboard or old carpeting is spread over the area and left for several weeks or even months during sunny, dry weather. This smothering will kill the roots and once the cover is removed the dead plant material can be removed to insure that there is no regrowth. If repeated attempts to eradicate fail and the problem is increasing, it may be time to consider some form of chemical control. There are more organic products being developed so try those before resorting to the more toxic chemical products. Always follow the instructions and take the necessary safety precautions when using any product even ones listed as “organic” or “natural”.

Perennial Weeds

1. Dandelion – Taraxacum officinale

Easily recognized by its bright yellow flower heads or fluffy gray seed heads, it is a perennial that spreads by seeds and branching taproots. Dandelions can be found almost everywhere and if left unchecked form thick colonies in lawns, parks and along roadways. Seedlings appear in early spring with smooth oval shaped cotyledons and grow into a basal rosette with irregularly toothed leaves. The flower buds form in the middle of the rosette. The hollow stalk which supports the flower leaks a sticky white sap when cut. Repeatedly digging out as much of the taproot as possible will weaken young and established plants and may cause their demise. If you know seeds have blown onto your lawn, you can apply corn gluten, a pre-emergent, in early spring. This will reduce the number of seeds that germinate, but do not use corn gluten if you want to reseed your lawn. Heavy infestations may require spraying; however, use spot spraying rather that general broadcast.

2. Canada Thistle – Cirsium arvense

A perennial that spreads by horizontal root stalks and seeds. Canada Thistle is found in home gardens, back lanes, fields and especially along roadways and undeveloped properties. Seedlings form in an oval and develop into a basal rosette of spiny irregularly toothed leaves. Often found in groups since they grow from the spreading root system. As the plants mature, erect stems form with prickly notched leaves topped by purple flowers that open in mid-summer. Gray seed heads follow and copious amounts of seeds are spread by the wind in late summer. Roots can go down several feet, so persistent, repeated digging and removal of as much of the root and any seedlings is the best way to keep control of this aggressive plant. Do not till as this will only spread the weed. Repeated mowing along roadways and undeveloped properties can control seed production as long as mowing is done before flowering.

3. Perennial Sow Thistle – Sonchus arvensis

Perennial and annual Sow Thistle are hard to distinguish. However, Perennial Sow Thistle has extensive light-coloured creeping roots that are easily broken. Seedlings form irregularly spaced elongated leaves with soft prickles along the margins. Erect, hollow stems contain a milky sap and form several branches that produce clusters of bright yellow ray flowers in mid-summer. Gray seed heads follow and seeds are spread by the wind, but also provide food for some seed eating birds. Perennial Sow Thistle is found in home gardens, field crops, along roadways and undeveloped properties and prefers moist conditions. In home gardens dig out and discard as much root as possible as it will regrow. This will require repeat digging so a thick, organic mulch can be applied once the plants are weakened; however, the thistles may still find their way through or around. Do not till. Sow thistles act as a host for viruses that can attack desirable plants.

4. Quack Grass or Couch Grass – Elytrigia repens

Recognized as coarse, slightly hairy blades attached to a tough whitish rhizome. This perennial weed spreads aggressively through these rhizomes that secrete a toxic substance which suppresses growth of surrounding plants. You want to keep it away from shrubs and trees. This grass grows everywhere and can quickly take over garden beds or areas of lawn if not controlled. Roots can penetrate deep into soil and creep under shallow barriers or through thin mulch. Persistent, continuous removal by digging out the root system and discarding is recommended. Do not compost or till as even small pieces of root will regrow. Solarize large patches. A last resort is chemical application, but this means you will also lose your adjacent plants. In undeveloped areas it becomes a ground cover that can be mowed to keep it from going to seed; however, if this area is ever reclaimed it will be very difficult to get rid of the extensive root system.

5. Broad-leafed Plantain – Plantago major

Perennial plant that reproduces by seeds produced on long stalks that form above a basal rosette of ribbed, oval leaves. Tough, fibrous roots make it difficult to pull out once it is mature. It thrives in moist, compacted soils along roadways and in lawns and quickly forms colonies if not controlled, so it’s best to find the seedlings and dig them out. Seed production continues throughout the growing season so mowing will spread the seeds. Birds like the seeds and Plantain leaves were used to treat insect bites.

6. Creeping Charlie or Ground Ivy – Glechoma hederacea

Aggressive low growing perennial with green scalloped round leaves and small blue flowers with a mint like smell when crushed. This weed reproduces by seeds and stolons that spread and send down roots forming new plants. It prefers moist, shaded areas and grows in gardens and will infest the lawn forming dense mats. Pull out and discard all plant parts. Do not mow or till as it will regrow. Use a thick mulch in beds, for heavy infestation in turf try to solarize. Can make cats or dogs sick if they eat this plant.

7. Orange Hawkweed – Hieracium aurantiacum

Oval elongated leaves covered on both sides with fine hairs form a basal rosette. Clusters of flat topped bright orange ray flowers are produced on top of single, hairy stems that contain a bitter, milky sap. Flowers are produced all summer. A creeping perennial that spreads through leafy runners that root, underground rhizomes as well as seeds. It grows along roadways, in hay fields, meadows and undeveloped land. Because the flowers make this plant attractive, it has found its way into people’s gardens and become a problem because of its aggressive nature. It is classified as invasive. Eradication requires aggressive, persistent digging and removal of all plant parts. Do not allow to go to seed since the dandelion like seeds can spread quickly. Do not till or compost.