thistle infestation

Bellevue, NE(Zone 4b)

My mom had a thistle bird feeder in her garden, and now the garden is infested with thistle plants. We have been weeding them and weeding them for several years now, and have been unsuccessful in getting rid of them. She is reluctant to use weed killer, becuase it would kill/damage her other plants. Does anyone know what to do about this problem?

Windsor, ON(Zone 6a)

GOOD LUCK! If you pull them and don't get the root. they will rejuvenate from the root. They are persistant SOBs. The only thing you can do is use a broadleaf weed killer such as killex. NOT ROUNDUP!! Killex will kill any broadleaf weed plant down to the root. If the roots go really deep, you may have repeats, but keep going. If they are in a garden and coming up in your plants, all you can do is keep pulling or get into the soil after a good rain and try to get the roots. I feel your pain as I too have been fighting the monsters for years. Don't be afraid to get deep into the soil to chase after roots. you'll be amazed at how persistantly deep the roots go. And you can see what I mean by rejuvinating by the root.

Dublin, CA(Zone 9a)

What I do is cut them off at the base, then paint weedkiller on the open wound where I just cut the stem off. Most of the time that kills them, occasionally they'll come back after that treatment but just repeat. To prevent the seeds from growing in the first place, I always microwave my birdseed for a couple minutes before I put it in the feeder, I think it tastes the same to the birds but it can't germinate so won't cause problems in the yard.

Bellevue, NE(Zone 4b)

Treating each individual plant like that is a great idea! We have pulled them so many times for 3 summers now, and my mom feels like she is making some progress, but she is putting in a ton of hours and wearing herself out doing it. I will let you know how it turns out if she is willing to try it.

Ayrshire Scotland, United Kingdom

If the weather is not suitable for working or weedkilling, then a temp measure is to deadhead the weed so at least they wont go scatter more seeds till you get to them when time/weather allows, Ecranes idea of painting weedkiller onto the damaged tap root or crushed leaves is a great way to work within a border that has other plants in it as you just paint the weedkiller onto the thistle and avoid contact elsewhere, hope you have some good results soon, good luck. WeeNel.

Issaquah, WA(Zone 7a)

Good advice on all of the above thistle and root control, but I am most amazed to read about the microwave birdseed! Ecrane that is a great idea! Would it work on blackoil sunflowers (all we feed the birds now) or would one get popcorn style sunflower meats? Only one way to find out, I guess. I'm just amazed at the concept- sterilize the seed!

A funny OT on the individual plant treatment, although it has indeed worked great on other plants for me: someone relayed that a family member either injected Round Up into roots or stalks of Japanese Knotweed -a horrible spreading weed/runaway ornamental here in WA and likely worldwide;
We have a stand of it spreading every year further and further into the woods. I foolishly decided to make a couple shade beds out of "their" area, and have had fair luck with constant plucking of new starts every year (despite digging as deeply as I could for knotweed roots during bed preparation.) But it gets tiresome picking knotweed every week or two..... and I do want to save the woods beyond as much as possible.

Soooooooo I remembered the Round Up injection report and that it helped control the knotweed pretty well. I spent hours on hands and knees crawling around my shade beds and woods , syringe and stout needle and jar of Concentrated Round Up trying to inject every cane I could see. Hundreds- at least 300, some small, some big bambooish adults. It's really hard to inject a plant! You don't know what you're aiming for, unlike a vaccination or lab draw, but I did it. I boldly injected where no injection had gone before.

How many knotweed stalks do you guess gasped and keeled over in the ensuing couple weeks? Out of hundreds? 5. FIVE! All that work lol... but it was good for a laugh and a lesson that I need to do more research on the topic.

I think thistle control using "snip and paint the open cut" would work well, but still a lot of effort to get each one. One at a time... and it will get done! Good luck.

Dublin, CA(Zone 9a)

I've been using the "cut and paint" approach successfully on my thistles and these things that I don't know what they are, but they look like dandelions on steroids with prickers. So far so good, they haven't been regrowing on me. It is a pain to do them one at a time, but as long as I only have to do it once it's fine!

And on the birdseed--I can't actually take credit for the idea of microwaving it so it doesn't sprout when the birds spill it. I read it somewhere but can't remember where (probably on here somewhere!) I usually have bags of mixed seeds so I'm not quite sure what all is in there, I usually get a really big bowl and fill it up and nuke it for 1-2 minutes, stirring halfway through to make sure all the seeds are getting heated. If you have less seeds I'd do it for less time, you don't want to cook/burn them, just mess up their reproductive potential. I've never had any popping/exploding seeds, I'm sure if you leave them in there for too long you might end up with something like that though!

Issaquah, WA(Zone 7a)

Wanderinggarden, are your thistles the short little fellows lying low to the ground or the tall 3-4 foot monsters that have pokers all the way up? We have those growing in a neighboring clearing (now overgrowing with opportunists) and they are tough to walk by without getting scratched.)

I think many weeds/undesireables can be beaten back by constant cutting: starve the root system by stopping photosynthesis. Have had success with blackberries doing that, but I have some dandelions that have roots like carrots from the same treatment. It's a constant battle, I'm afraid.
I did it ecrane: Kitchen Physics with Sunflower seeds!

1.5 cups of black oil sunflower seeds in Tupperware with lid and steam vent opened. Microwave on full power and the results follow:

@30 seconds- warm sunflower seeds
@60 seconds- warmer seeds, slight oiliness felt and seen on bowl sides
@90 seconds- beginning to steam, more oil emerges so that some seeds stick to bowl sides
@120 seconds- real steam, smell of sunflower nuts and beginning to pop!
@150 seconds- more steam, a few more kernels burst, smells great
@180 seonds- supper is ready! For the birds, not me. There was no further popping, maybe 10 kernels total. I will cool them, put them in a feeder and see what happens.

This is the greatest thing. We love feeding the birds but had to give up on millet long ago for the forest of millet that grew beneath any feeder. Even if you can't take credit for the idea, thanks for passing it on to DG.

Dandelion on steroids with pokers? I'd be curious to see a photo of one if you haven't killed them all. Our big menace is buttercup: rampant through the lawn, such a pretty yellow flower, and yet so bothersome and aggressive.

Dublin, CA(Zone 9a)

I wonder how popped sunflower seeds would taste? Did you try one? Could be the a new delicacy that will make you a millionaire!

I still have my south hill to weed so if I think about it I'll take a picture of the prickly dandelions on steroids and post it here so you can see them, should probably post it on the ID forum too so someone can tell me what they are!

Dublin, CA(Zone 9a)

I started a thread in ID forum to find out what my dandelion things are--here's the link if you want to see the pictures

Issaquah, WA(Zone 7a)

Indeed I tasted them, Ecrane, the kitchen aroma was impossible to resist. I had 5 for a good appetizer and they tasted excactly like unsalted sunflower seeds one would buy in a package at the grocer. Now if we'll do this regularly enough to see if fewer sunflowers sprout below the feeders remains to be seen. We have a voracious herd of grosbeaks, finches and the usual juncos and chickadees. All feeders are filled at least once daily. And then there's that pesky black bear..... ack!

off to the pokey dandelion link... thanks again for the bird seed idea!

Fishers, IN

I'm new to this gardening thing and thistle has quickly become my enemy. What do you mean when you say 'paint' the weedkiller on the new cut? All I can think is the Roundup is either straight spray or foam. Thanks for the warning on thistle in the bird feeder - I was just getting ready to put one out there to attract finches!

Columbia, MO(Zone 5b)

Most weed killers are a liquid with a spray attachment. Just remove the spray head and dip a cheap paint brush in the liquid and dab the liquid to the fresh wound on the plant. Be very careful not to drip any on the plants that you want to keep as it will kill them too. By doing it this way it tends to be more effective as the poison is more readily absorbed by the weed.

Dublin, CA(Zone 9a)

Or if you don't have any plants super close to the weed and you've got good control with the spray nozzle you can do it that way too, just get the nozzle close to the weed and squeeze carefully. But if you have a lot of plants around the weed, the paintbrush gives you better control over where the weed killer goes.

Tuscaloosa, AL(Zone 7b)

I have read of some who cut the bottom out of a large nursery pot, put the pot over the plant, and then spray into the pot and onto the weed. I haven't tried it, but it sounds to me as if it would work and would keep the spray away from nearby plants.


Windsor, ON(Zone 6a)

I did that to a weed growing on the edge of my garden bed. I didn't want to kill te grass so I took a grocery bag and made a hole on the bottom, pulled the weed thru and sprayed it with Wipe-out (a round-up cousin that is available in Canada.) It worked like a charm. Weed died, Grass remained.

Tampa, FL(Zone 10a)

If the thistle is an annual buy Preen, read and follow label directions.

It is a product that stops seeds from sprouting, should cut down on your work load.

Nothing is 100%, but it will be a big help, I use it all the time on my jobs.

Thumbnail by DaleTheGardener
Windsor, ON(Zone 6a)

Unfortunately they are perennial and if they are already there Preen won't work, but it will prevent new seedlings from sprouting.

Delray Beach, FL(Zone 10a)

I used to grow dipsacus laciniatus. Now that's a weed on steroids. Here is a link to it:

I miss them.

Issaquah, WA(Zone 7a)

dale_a_gardener you need tell that place to get some table and chairs right there in front of those wonderful plant and color combinations~! Eye catching, for sure.

Bellevue, NE(Zone 4b)

So I couldn't get online for a bit, sorry. The thistles grow really tall, some of them were as tall as I am at 5' if you don't get them right away. My mom has been trying to starve them of photosynthesis by constant pulling this summer, but we have pulled and pulled those stubborn weeds so many times that I get exhausted just thinking about it. I have moved away and can't even help her with them anymore, so I am glad she has something new to try to get rid of them.

Fishers, IN

Thanks so much for all the help. Sounds like many of us have 'thistle-issues' (!). I know I've reached an OCD level about them because I was awake during the night for about an hour trying to think up a plan to eradicate them! I know one of the local nurseries suggested covering them with a bag before cutting them, especially if they'd gone to seed, then using a thick surgical glove over the gardening gloves and actually working the chemical all over the remaining stem. Sounded like a lot of work to me, but in the long run, I'm beginning to think it might be worth the extra effort.

Delray Beach, FL(Zone 10a)

I would rent a backhoe, dig up the infested area to a depth of 2 feet, dispose of the soil at the dump and start a new bed with fresh soil. But then again, that's just me and my totalitarian way. I could be wrong.


Ayrshire Scotland, United Kingdom

Sylvain's idea sounds good, but if you dig, break or just wound these roots in any way, they rise up and wave at you for the tickle you gave them and ofcourse, its like dead heading, you just get more new shoots growing, if it is too much all at once to weedkill each plant, keep pulling the flowers off till you get to the plants and at least you are preventing a new generation of plants, no seedheads equals no new plants, that way, you will have a bit of time to play with for weedkilling. hope you get on top of it, you want to try do it before the winter as they will go into their dormant season and the weedkillers wont work because the roots wont take it down to the roots you are trying to kill. good luck WeeNel.

Milwaukee, WI

Thanks for all the info on getting rid of thistles. Just bought some Round Up the other day. Will try cut and paint method. Sounds like it should work. Will let you know.

Marquette, MI(Zone 5a)

Our Soil Conservation Agency held a session on invasive plants. One of the real thugs was Bull Thistle. They reported that Roundup and it's cousins were only mildly effective. Their recommendation was to cut off the stalk and, using a small funnel, pour salt into the open stalk tube. They reported that it was time consuming but effective.

Also, niger thistle, which is commonly sold for bird feeding (also spelled Nyjer) is supposed to be heat treated for sterility before it's sold.. This site states that it's flower is yellow and not purple.

We have a problem with Bull Thistle, especially down by the creek.

Ayrshire Scotland, United Kingdom

I hate to admit this, but the Thistle is our national emblem, the big fat purple thistle that has needles like bread knifes, needless to say, not many folks grow it as a garden plant and for some unknown reason, it seams to be dying out (have you visited Scotland with your weed killer lately Ecrane) ha, ha, ha, but to be honest, all the thistle family are known to spread like wildfire wherever you find one, you get a million the next year and the only sure way to rid them is dead heading soon as you see the buds appear, then weedkiller the foliage/roots, the tap roots can go down several feet if you dont kill them when young plants, the problem with the seed-heads are when the dry off and go white, they have thousands of seeds that are attached to a little furry hairy bit that allows the seeds to soar miles away in the breeze, a bit like the seeds of the Dandelion, unfortunately, many of the seeds just settle a few feet apart and next year you are infested, last year the flower industry used the fat purple headed type as flower arrangements shipped from over seas, so I guess we will have them growing everywhere once again, good luck with your weed-killing, hope you have much cleared ground by next year. WeeNel.

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