What’s Up with Weeds?

Stories You May Like

In the Hill’s Natural Dye Garden, A Rainbow of Color Is in Bloom

Student Project Brings ‘Healing and Honoring Garden’ to Akwe:kon

Garden at Cornell Health Brings Nature’s Balm to Ho Plaza

There are reasons why they grow a lot faster and hardier than your lawn and veggies—but a CALS prof has advice

By Beth Saulnier

“As I tell my students, there are three sure facts in life,” says CALS’ Antonio DiTommaso, “death, taxes—and weeds.”

The latter, he jokes, is “job security” for him: DiTommaso is a professor of weed science, devoting his career to studying those tenacious, herbaceous adversaries of industrial-scale growers and home gardeners alike.

About 15 years ago, DiTommaso spearheaded the creation of Cornell’s Weed Science Teaching Garden—open to the public and boasting more than 100 species.

Professor Antonio DiTommaso

His student teams participate in annual weed-identification competitions, held regionally and internationally.

(And you can skip the jokes about mind-altering substances of the smoked and edible varieties; he’s heard them all before.)

DiTommaso co-authored the seminal reference book Weeds of the Northeast, published by Cornell University Press and now in its second edition.

The cover of "Weeds of the Northeast"

With gardening season on the horizon for much of the U.S., Cornellians tapped him for some thoughts on how to deal with weeds—and why some can be more friend than foe.

Would you define: what is a weed?

The first thing I do in my introductory weed science class is ask that question.

Some students will say a weed is “a plant out of place” or “a human construct.”

Ralph Waldo Emerson said, “a weed is a plant whose virtues have yet to be discovered.”

So … what is it?

It depends.

From an agronomic perspective, it’s a plant that competes—for nutrients, water, and other resources—with the ones that we want to grow. But a naturalist would look at, say, common milkweed as a native species that’s the only food source for the monarch butterfly.

So weeds have some benefits?

They do. For example, they provide erosion control and can grow during droughts. They’re basically the wild relatives of our crops, so they have a lot of traits that allow them to survive. They grow between cracks in the sidewalk; none of our crops can do that.

What are some tips for weed management in a household yard?

One important thing is, make sure you don’t mow the grass too low; leave three or four inches rather than scalping it, to allow it to compete for light, because weeds are much more adept at growing rapidly.

They’re basically the wild relatives of our crops, so they have a lot of traits that allow them to survive.

Don’t overfertilize, because weeds are much faster than any turf grass at uptaking nutrients. In the fall, you shouldn’t rake leaves; just mulch them. That provides nutrients and improves soil health.

The other key thing is not allowing the weeds to go to seed. Depending on the size, each plant—such as common lambsquarters or pigweed—can produce 50,000 to 100,000 seeds, and they don’t all germinate at once.


There’s an adage, “One year of seeding equals seven years of weeding.” That’s because of seed dormancy, which is a trait that has been bred out of our crops; no grower wants to plant corn and only have 50% of it come up.

But the wild relatives still have that trait, and it’s a great survival strategy. Why put all your eggs in one basket? If germination is staggered, it’s OK if you miss one year because it’s too wet; you might do great the next year.

How about battling weeds in a home garden?

One thing I like to stress is that having bare, tilled soil is a perfect situation for weeds to grow. They’re stimulated by light, and they have structures that can sense that there’s no vegetation above them, so they should “go for it.”

There’s an adage, 'One year of seeding equals seven years of weeding.'

You want to practice minimum tillage; just work the soil where you’re going to plant. You can also use tarps or straw mulch; anything that protects the soil is usually helpful in keeping the weeds down.

And in the fall, be vigilant about uprooting any weeds; remember how many seeds they can produce.

After pulling weeds, is it OK to throw them on a compost pile?

Yes, as long as they haven’t produced seeds. The only weed that I would not recommend composting is a succulent called common purslane.

Stories You May Like

In the Hill’s Natural Dye Garden, A Rainbow of Color Is in Bloom

Student Project Brings ‘Healing and Honoring Garden’ to Akwe:kon

It’s got so much moisture that even three days out of the ground, it can reroot itself. I tell gardeners: put it in a black plastic bag on a hot, sunny day, and really fry it.

Common Purslane
Not for composting: Common purslane.

If someone doesn’t want to use chemical herbicides, are there other things that can be used to kill weeds?

You can spray vinegar on it; it won’t kill the entire plant, but will usually burn the top. If you’ve got weeds coming up between the pavement, you can pour boiling water on them.

A solution of salt in a high enough concentration will kill weeds. And of course, many commercial organic products have been around for years.

Why do weeds seem to grow so much faster than other plants—the ones we actually want to succeed?

They’ve adapted such that they invest everything in reproduction, and their life cycle is short; they have tens of thousands of seeds, whereas an oak tree that lives for 100–300 years takes 20 or more years to start producing acorns.

They’ve adapted such that they invest everything in reproduction, and their life cycle is short.

As much as we hate weeds, that can be a positive: because they’re so quick to grow, they play an ecological role by protecting the soil when it’s been disturbed by humans or a natural disaster.

Are some weeds especially worrisome right now, due to climate change?

Yes. I’m actively involved in research on what weeds we should be concerned about, in the Northeast in particular—things that have been problems down south, but which we never really worried about because our winters were cold enough to keep them at bay.

Professor Antonio DiTommaso, in the Cornell Weed Science Teaching Garden
DiTommaso in the Weed Science Teaching Garden.

One is kudzu, which is often referred to as “the weed that ate the South.” It can shade out trees, climb right over them, and cause saplings to topple during windstorms. It’s of particular concern in the forest understories of natural areas.

For many years, I was hoping it would never get to New York State—but now it’s in the lower Hudson Valley and all over Long Island.

In the end, are the weeds always going to win?

I don’t minimize how challenging it is. I mean, we’ve been at this game for over 10,000 years, in terms of when agriculture got started.

We’ll think we’ve got a great herbicide and then we have resistance issues. For example, some weeds have adapted to glyphosate—the active ingredient in Roundup—and we can’t use it to control them anymore.

Kudzu vines
"The weed that ate the South."

Let’s end on a cheery note: is there a plant widely considered a weed you’re actually fond of?

Dandelions! In the Italian-Canadian community where I grew up, we’d eat them in the spring when they’re young and tender; they’re very nutritious.

In fact, a colleague just sent me a book he wrote—it’s in French, but the title translates as Dandelions Against Lawns: A Story of Love, Hate, and the Lawnmower.

(Top: Illustration by Caitlin Cook / Cornell University. DiTommaso photos by Ryan Young / Cornell University. Weed images provided.)

Published April 29, 2024


  1. steven weisbroth, Class of 1956

    Dr. DiTommaso- you might be interested in another nontoxic, nonchemical means of eradicating weeds that grow in cracks of brick walks, patio flagstones, etc. that I have used for years. I heat water in our electric teapot and sprinkle several ml. on each weed growing in the cracks, especially on the base. it works almost instantly. I simply go on a weed patrol one every couple of months to keep the same area free of weeds.

    • Patti Martin, Class of 1979

      He mentioned pouring boiling water on weeds. Is your solution any different?

  2. Evangeline Loh, Class of 1995

    This article was sensational. I’ve noted (observation, no statistics) that weeds seem to be evolving (Austin, TX). There are so many more species of aggressive weeds: thorns, bristles, spikes. It has been fascinating. Is there any data to support this?

  3. Don Cameron, Class of 1963

    Interesting. Living in the UK we have a whole different suite of weed species, but the problem is the same.

  4. john ketz, Class of 1972

    interesting and thanks for sharing
    keep up the good work

  5. Joseph Sarbinowski, Class of 1987

    Enjoyable and insightful article. I favor any organic answers that continue to evolve to these problems as I fear the adverse impact of chemicals, etc as an answer. Living in suburbia, it is hard to accept some weeds but I have learned to not get manic over them.

  6. Jeff Woodring, Class of 1993

    GREAT article and PERFECT highlight of how “Any Study” can evolve into something that touches so many aspects of human existence.

    Bravo to Cornell and Antonio DiTommaso!!

  7. Kenneth LaPensee, Class of 1969

    I’m having satisfactory results planting and growing clover (and not killing dandelions), considered by many to be a lawn weed. It is a legume that fixes nitrogen from the air to fertilize itself and supports pollinators. I’m using it to combat stilt grass weed, which grows so densely that it smothers tree saplings and can only be controlled for the long term by persistent mowing. Clover tolerates shade from my trees and is filling in the large bare, dry shaded spots under the trees created by leaf blowing and mowing. Finally, it is soft to walk on and attractive as a ground cover.

  8. Elisa Bremner, Class of 1990

    I’ve learned a lot about native plants over the past few years, and things I used to pull out as “weeds” turned out to be quite beneficial for the pollinators! I do know that a perfect lawn is an ecological wasteland, so I no longer spend hours pulling dandelions and violets.
    Our invasive weeds here are mugwort, garlic mustard, oriental bittersweet and Japanese knotweed. Plus those non-native ornamental bushes like winged eponymous and multiflora rose. These may have been brought here because they looked pretty, but they are crowding out real food for our birds and insects. 🙁

  9. Joni Eisen, Class of 1968

    Great article – but I’m surprised you mention destroying purslane, but not eating it. It’s actually delicious and nutritious – although it should be eaten in moderation because of high oxalic acid content. I’m always glad to see it begin to appear in my San Francisco garden – which just happened yesterday!

  10. Joanne Irby, Class of 1996

    I’ll need to look up some dandelion recipes, given the nutrient value … easy to find those in my yard!

  11. Andrej Sierakowski, Class of 1997

    Purslane, I have read, is an edible weed/succulent that I have grown as potted plants. Can you comment on the validity of purslane as an edible plant. I also have read that purslane is high in omega 3 fatty acids and is a lower cost alternative to eating fish containing omega 3 fatty acids such as sardines, salmon, mackeral and, chilean toothfish (sea bass). Can you comment Dr. DiTommaso further on purslane’s usefuleness as a dietary option ?

  12. Marty Newhouse, Class of 1994

    Great article… My property in northern Virginia is currently being overtaken by lesser celandine, a non-native, invasive species — in wooded areas, lawn, and garden. Everything I read says the only viable options for managing it are to use glyphosate (which I don’t want to do) and pulling it out (which is not practical given the magnitude of infestation). I’ve also read it should not be composted… If anyone has experience dealing with this plant, I’d love to hear more.

Leave a Comment

Once your comment is approved, your email address will not be published. Required fields are marked *

Other stories You may like