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All about those pesky garden weeds

WTIP’s Northern Gardening

Weeds in the Garden and Invasive Weeds in Cook County

This program aired from 4-5 p.m. Thursday, July 1.
The guests were Molly Thompson, Sugarloaf Interpretive Center executive director and Ann Rosenquist, CSA grower and U of M Master Gardener

The program was hosted by Diane Booth, Cook County Extension, and Joan Farnam, Northwoods Food Project

Photo: Canada Thistle

Molly Thompson, executive director of Sugarloaf, discussed invasive/noxious weeds on the program. Sugarloaf Cove will hold a workshop on identifying noxious weeds/invasive plants on Saturday, July 17 at 10 a.m.  Participants will learn how to identify non-native invasive plants, how they threaten our North Shore forests, and what you can do to control them on your property. All participants will receive a full color guide to invasive plants. Free.

Also, if you want some hands-on experience to help you identify invasives and learn how to control them, Sugarloaf is holding “Attacking Invasive Work Days” every Thursday at 10 a.m. in July and August. The public is invited. 

For more on Sugarloaf Cove, visit 

Here is a site that has photos and discussion of the primary noxious weeds in Minnesota.

And here’s an interesting boadleaf and grass weed seedling identification key from the U of M Extension office:


Here are excerpts from the program notes about weeds in your garden. 


What is a weed?

A plant that is in the wrong place. 

For example: Some orchids in Hawaii are considered weeds, so are nhasturtiums in California.

What about the dandelion? When it comes to nutritional value, Taraxacum officinale is no slouch. The plant is rich in vitamins C, A and D, iron, calcium, magnesium and potassium. And, it gets good marks as a source of fiber and vegetable protein. It was brought here to provide greens. 

Why have we come to look upon the dandelion with a jaundiced eye? Quite likely, it was the idea of a perfect lawn that prompted us to take up arms against this esteemed plant. Now,

the dandelion’s commercial value stems mostly from the arsenal of weapons we purchase to use against it.


Or, as Ralph Waldo Emerson wrote: “A weed is a plant whose virtues have not yet been discovered.” 


What is the difference between a common ordinary weed and a weed that is considered to be invasive?

The important biological difference between invasive plants and garden weeds is the ability of invasive plants to disperse, establish, and spread without human assistance or

disturbance. Because of this, they are much more problematic in natural environments than are typical weeds.

Here are some suggestions about what to do about weeds.

1 . Healthy, vigorous plants are the best defense against weeds. Make sure your plants are not under stress such as lack of water, drought, temperature or poor drainage.

2 . Plant species or varieties that are best suited for the environment you are planting them in.

3 . Make sure your soil is nutritious – low fertility may encourage more weeds.

4 . Don’t overuse fertilizers or herbicides.

5 . Mowing, tilling or weeding practices are very important to reduce weeds (2” deep). However, every time you till or dig you are bringing up more of those dormant seeds and may be allowing them to germinate.

6 . Actively use as much of your garden space as possible so there are fewer places for weed seeds.

7 . Actively monitor your landscape or garden so you can catch weed issues early on.

Important things to know about weeds to help control them:

• Use herbicides only as a last resort, and then  sparingly.

• Follow IPM (Integrated Pest Management): Balancing a weed-free garden with a healthy environment.

• Know what species your weeds are so you know if they are a spring annual, a fall annual, a biennial or a perennial weed. Your management techniques will vary based upon the knowledge you have about the plant and its life cycle.


Spring / Summer Annuals: Germinate in the spring and mature during the summer like crabgrass, foxtail grass, knotweed. They only live one year. Allowing 2-4 inches of mulch to remain on the soil in the spring will prevent these spring annuals from germinating without sunlight.

Planting early spring ground covers like wild ginger, violets, or lamiastrum can compete with the weed

seeds and reduce the vigor of the weeds. 

**Some ground covers can become invasive, so you need to know which ones to avoid, like goutweed (Aegopodium podagraria). Call the Extension office at 387-3015 for more information.


Fall/Winter Annuals: Germinate in the fall, usually overwinter and then bloom and form seeds in the spring. Only live one year.

1 . Examples are chickweed (Stellaria media) field penny

cress (Thlaspi arvense), Shepherd’s purse (Capsella bursa-

pastoris). Eradication of these in the fall when younger

and weaker is better than waiting until the following spring.

A cover crop like winter rye (Secale cereal) can help

reduce the fall or winter annuals germinating by providing


2 . Early cultivation in the spring can also help to eradicate

these fall / winter annuals. Plant early growing vegetables

in these spaces like spinach or broccoli (cool-season crops).

That will shade out and maybe prevent germination of

these fall / winter annuals.


Biennial Weeds: Take two years for their life cycle and they

die. Usually green foliage the first year and flowers and seeds

the second year. These are often grouped with perennial weeds

because usually the control measures you take against them are the same as perennial weeds. Bull thistle, spotted knapweed, mullein, garlic mustard are all examples.


Perennial Weeds: Usually have thick, fleshy roots that can store

lots of food so they can come back again and again and again…it

takes time and effort to get rid of these. Often will reproduce

both by seed and by stolons, rhizomes and small pieces of roots

left behind. Some may have an allelopathic effect on plants

surrounding them. Examples are Canada thistle, orange hawkweed

and quackgrass.

Cut down the weeds in the area you want to plant. Cover with an old carpet or something thick and heavy, weigh it down with rocks. Periodically over the year, remove the carpet, remove any of the weeds that have come up, and then replace with the carpet. Over a year of maybe two – all of the energy reserves in the root

have been depleted.


Lasagna gardening is another way folks start a new garden in an area where grass/weeds are already growing. 

To build one,  pile organic matter like leaves over a proposed garden area, cover with heavy black plastic or landscape fabric and weigh it down. Leave for at least one to two years. Lift up the plastic and you will find a nice garden bed area.

To create a lasagna garden in an existing garden, put down newspaper and then about 4 inches of mulch. 


Other ways to control weeds:

•  Use rhubarb leaves as mulch over the areas you want to cover.

•  Remove weeds, grass the area over and keep it mowed repeatedly. The grass may choke out the weeds. Then you can go back and remove the sod to plant the area.

•  Root attack – Take a broad fork and dig up all the roots you can, sift the soil to remove as many pieces of the roots as possible. Then be very vigilant to remove any other pieces that show up.

•  Leaf attack – Keep removing all the leaves and over time it will hopefully drain the resources of the plant. This does not work well if it is attached via rhizomes or stolons to other plants nearby and you are not removing those leaves.

Individual root attack – one root at a time – dandelion, sow thistle, etc.  You can make weeding easier and remove more of the roots if you weed right after a rain when the soil has been loosened up (don’t compact the already wet soil).

Flame throwing or burning is most effective on annual weeds but not perennial or biennial weeds.

• Dig it up and start over. If 30% or more of your perennial garden is infested with weeds you may want to pot up your perennials so you can attack the weeds and eradicate as many as possible. Dig out as many as possible, remove as many by hand as you can, maybe even sift the soil for root fragments and then replant and mulch.

Perhaps the most important tip is --- keep on top of the weeds in your garden. Getting them out when they're just sprouting is a lot easier and more effective. And, if at all possible, get them out before they bloom.

For questions or comments, call WTIP at 387-1070 or e-mail For questions about weeds and controls, call Diane Booth at the Cook County Extension office at 387-3015.
And thanks for listening!