How to Get Rid of Thistles and Bamboo Weeds

Thistles and bamboo weeds are some of the hardest weeds to kill. That's because they often spread by rhizomes or runners underground. With some effort, you can get rid of thistles and bamboo weeds organically.

What is Thistle?

A thistle is a weed characterized by its sharp, prickly leaves and often showy purple-hued flower heads. Depending on the type, thistles may be biennials or perennials. They spread by both seeds and their spreading root system, making control difficult and a multi-step process.

How Thistle Weed Spreads

Thistles spread two ways: their seed heads and their root runners. This means that a multi-step approach is usually needed to get rid of thistles from lawns and gardens.

How to Kill Thistle Organically

Getting rid of thistles is a often a multi-pronged approach throughout the growing season. Here are steps to take.

Stop the spread of seed heads

Those pretty purple flower heads contain hundreds of seeds that easily spread. If you see a thistle flower, immediate cut off the flower head, place it in a plastic bag and throw it away. Because the composting process most often doesn't get hot enough to kill the seed, don't compost the flower heads. Also, because thistle seeds and other weed seeds grow best on bare patches of dirt, try not to leave bare patches in the garden or yard.

Weaken the plants

Repeatedly cutting the thistles at ground level will weaken the plants. If you only have a few thistle plants, digging them out also works. Planting other plants that compete for sunlight, water and nutrients can also weaken the plants.

Mulch heavily

Mulching suppresses weeds. Because thistles spread by root runners, mulch beyond where the thistles are growing. Using a weed barrier mat and then placing a thick layer of wood chips or other mulch can help.

Use vinegar

Many gardeners use vinegar to kill grass. Horticultural vinegar, which is more acidic than vinegar found in the grocery store, can also be used to kill thistles. Before spraying the thistles, mow the thistles to the ground. Note that vinegar will make your soil more acidic.

What is Bamboo Weed?

A member of the grass family, bamboo is characterized by its woody stems and often very tall growth. While hundreds of bamboo varieties exist, they fall into two types, clumping and running. Japanese bamboo weed or Japanese knotweed is not technically bamboo, but is invasive.

How Bamboo Weeds Spread

Bamboo that spreads in clumps is slow to spread. While it may have a huge root system, it can be dug up. Running bamboo spreads by runners and is often invasive and hard to control. Its runners or rhizomes can spread more than 100 feet from the original plant. You can learn more about Good and Bad Bamboo.

How to Kill Bamboo Weed Organically

Controlling bamboo weed that spreads by runners is often a multi-step process. Here's how to get rid of bamboo.

Weaken the Plants

Repeatedly mowing the plants down to near the ground level will weaken the plants over time. This may take a few years. You can also weaken the plants by manually removing them. Because they spread by runners, you can expect regrowth.

Create a Barrier

If the bamboo spreads by runners, then a bamboo control barrier will stop its encroachment. The best barriers are made of concrete or metal. They should be about 2 ft. deep below ground and extend at least 6 inches above the ground. After building a barrier, monitor the area frequently for any bamboo plants that may cross the barrier.

Use Horticulture Vinegar

Horticultural vinegar is more acidic than vinegar found in the grocery store. Before spraying the bamboo, mow the bamboo to the ground. Note that vinegar will make your soil more acidic.

Other Methods For Getting Rid of Thistle and Bamboo Weed

People have used other methods of getting rid of thistle and bamboo. Managed livestock grazing programs have been used to get rid of both thistles and bamboos. Some herbicides and other weed control products have also been used. For other ideas for getting rid of bamboo and thistles, contact your state extension service. They may know other methods that work best for your area.

Prevention

The best way to keep thistles or bamboo from invading your garden or lawn is to monitor them frequently. If signs of thistles or bamboo are found, begin taking action when there are just a few visible plants and before a giant underground root system has developed. While thistle and bamboo are some of the most difficult weeds to control, knowing how to kill weed seeds also helps.

Expert Advice

Question. Mike: A neighbor planted 'running' bamboo as a "natural fence" around his property, and not surprisingly, it's out of control. The culms are about 12-16 feet high; both plant and root system are invading my property. It also blocks out the sun and sucks up all the available water so that I can't seem to get anything else to grow in my backyard. I've read that bamboo is technically classified as a "perennial grass" which means that growing it violates a township ordinance requiring grass and weeds not to be higher than 10 inches. If the township orders it to be removed, how do we get rid of it safely without damaging the environment? Thank you.---Curtis in Cherry Hill, NJ.

Hello, Mike McGrath: What can you recommend to get rid of thistles in my garden and lawn? I have tried extreme weeding and professional chemical treatment, but they're back!!!!!!! Thank you.

---Valerie, Rockville, MD

style="font-weight: bold;">Answer.  These are two of the toughest weeds you can face, especially the bamboo, which 'runs' at an astonishing rate and will happily take over acres I fallowed to— although your terminology is somewhat off, Curtis. Those aren't plants AND roots invading your domain—its one big plant with one giant honkin' root system that expands to cover the earth like horticultural concrete a few inches under the surface. Some thistles form similarly impenetrable root systems. (Val— never let thistles flower; if you do, then you've got roots and seeds to worry about!)

These are not easy plants to beat, and as Val discovered (Bad girl!), toxic chemical herbicides won't do the trick. Those poisons are good at killing off single plants, but they don't affect huge underground root-systems; so don't waste your time, money and life fooling around with them.

There are three basic ways to do the job well and safely, all of which involve you first cutting the above ground growth to the ground repeatedly. Cut it all down, allow it to grow again; cut it all down again, let it grow again, etc. Two, three, four times; the more the better to deny the roots their solar energy collectors. In fact, if you just do this continual cutting for several years, the plants and roots will eventually die.

For more immediate satisfaction, cut and then do one of the following:

1.    To kill a patch on your property alone, mulch, mulch, mulch the entire area with something THICK and HEAVY (sheet-metal, old carpeting …) weighted down with a few inches of soil or woodchips on top. May be soak the area with a high-strength vinegar (see #3) first. Make sure the mulch extends a good couple of feet past where the plants were growing. Regardless, the root system will likely send plants out on a scouting mission and try to creep up around the edges. Be vigilant, and mulch these pioneers and/or spray them with high-strength vinegar. Leave the mulch in place for at LEAST a year. Or better still, leave it there forever, and make a nice raised bed filled with 'wanted' plants over top. READ COMPLETE ANSWER
1. 2.    If the bamboo is spreading to your property from a neighbor's place and you just want to keep it on their side, cut yours down and drive barriers deep into the ground at the property line to keep more from spreading over. Then use high-strength vinegar and/or mulch to kill the roots on your property.  

Here's some barrier info from one of our favorite sites, www.Americanbamboo.org (this is also a great place to learn more about bamboo—not all types are bad; there are many well-behaved varieties that grow in tidy clumps): "To prevent running bamboo from spreading, a "rhizome barrier" two or three feet deep is essential. It should be slanted outward at the top so that when the rhizomes hit the barrier they will bend upwards. A barrier does not stop a running rhizome; it only deflects it. The barrier should project an inch or two above ground level. Check the barrier once a year, and cut off rhizomes that arch over the top.

"Barriers can be concrete, metal, or plastic. The usual recommendation is high-density polypropylene (40mil or heavier), glued, taped, or clamped with stainless-steel at junctions. This material comes in rolls or as hinged sections, and is available from some landscape suppliers and bamboo nurseries, frequently termed root barrier. More elaborate barriers with corner posts that hold the material at the proper angle are also available."  McG: We don't need more plastic in the world, so I strongly suggest metal instead of the poly.  

Essentially what you're doing here is building an underground fence, and before you can build that fence you'll have to dig a trench to hold it. (Unless you have John Henry illusions, rent a machine to do the job.) And, if you make it wide enough; say a foot across; that trench alone will make an excellent bamboo barrier. Even better, turn your problem into a water feature! Dig a deep trench in between you and the bamboo/thistle/other super weed and then fill it with water and make it a kind of canal running along your property. Put in some fish and some a quatic plants and you're happening! (Like vampires, these weeds can't cross over running water.)

3.  And then there's the favorite high-intensity weed-killing solution of YBYG listeners, high strength vinegars.

Cut everything down, wait till the soil is bone dry and no rain is predicted for at least a few days and then, in the heat of the day, soak the earth containing those unwanted roots with one of the products below. (Be careful; you must wear protective gear, especially safety glasses). The high acidity of the vinegar will lower the soil pH down to something like 3—the surface of the moon. All plant and soil life will die, earthworms and larger creatures will quickly run or squirm away and that region will become a dead zone. Leave it like that for at least a month—longer if you can. (And if you fear that 'your' plant has more lives than Christopher Lee in an old Dracula movie, do it again a week or two later.) When you're sure it's really most sincerely dead, raise the pH back up with wood ashes or lime to between 6 and 7 (use teststrips or a meter) and soil life will return and the ground will be fertile again— but the roots will stay dead.

"Burn out weed killer" is St. Gabriel's Labs mixture of vinegar and lemon juice; it now also contains clove oil and is called "Burn Out II"(the sequel!)— but this is for normal weeds; it's not strong enough for things like thistle or bamboo. They recently introduced a double-strength version called "Poison IvyDefoliant" that should do the job. St. Gabe's products are available at retail outlets or direct from them at 800-801-0061; www.milkyspore.com.

"Green sense 20% acidity vinegar" is white vinegar that's four times more potent than the household variety. ("You watch the weeds die.") Its available in some retail stores in the Southeast, and Rohde's in Garland, Texas (near Dallas) will ship you a gallon for $11.95 plus $8.50 shipping; call 972-864-1934, or visitwww.beorganic.com and enter "white vinegar" in the search function. (There's a photo at www.greensense.net) Although, this stuff is incredibly powerful, it is all-natural—and not all high-strength vinegars are. The folks at Rhode's stress that their Greensense product is a grain based vinegar, not a petroleum-based product like the Acetic Acid used in photography.  Once it's done its work, a grain-based vinegar will return its nutrients to the earth, and allow life to colonize the soil once again. Chemically produced acetic acid will leave toxic resides that will destroy soil life for perhaps years to come; don't use them.style="font-weight: bold;">SAFETY NOTE: All of these products require extreme caution on the users part, especially the 20% vinegar! This is not harmless stuff! Vinegar with such enormous acidity is really caustic! You have to be careful not to get any on your skin or eyes--gloves and goggles are a must!!!!

And that, dear readers and listeners, is why many of you asked Rhode's to come up with something a bit gentler, and they did. (And yes, they tell us, it was entirely at the request of YBYG listeners, from whom most of their mail-order sales come! Thank you, Rhode's!) The new creation is "Greensense 10% Acidity vinegar";  $7.95 plus $8.50 mail order. You'll have to use it more than once (the 20% is like dropping a 'natural nuke' on those roots), but it is much safer to handle. "You pays your money and you takes your choice."

"Greenergy Blackberry & Brush Block", 8% vinegar (apple cider or wine) and 5% citric acid, is a West Coast product (apparently, wild blackberry vines attack people's cars and children out there). You can get a gallon from Professional Turf Center in Portland for $36 (includes shipping); call 1-800-894-7333(Regular household 5% white vinegar will only kill 'easy' annual weeds.)

You Bet Your Garden   ©2004 Mike McGrath