Getting Rid of Hoary Cress - Ask Extension
What is the best way to get rid of Hoary Cress? What herbicide is best and safest for humans and dogs in a residential yard.
Knowledgebase
Getting Rid of Hoary Cress #927736
Asked April 07, 2026, 1:46 PM EDT
What is the best way to get rid of Hoary Cress? What herbicide is best and safest for humans and dogs in a residential yard.
Larimer County Colorado
Expert Response
Hi Mandy,
This looks more like purple mustard? But it's definitely a type of mustard, which both hoary cress and purple mustard are.
It looks like this is in landscape beds and not the lawn? The biggest thing would be to make sure the weeds don't go to seed to break the seed production cycle. So mowing them now is helpful. It's a winter annual, so it will germinate in late winter/early spring and go to flower and seed before it gets too hot.
If you want to use an herbicide, anything non-selective will work - this could be glyphosate, organic "burn down" products, horticulture vinegar, etc. Lawn weed control products are not legally labeled to use in landscape beds.
Using mulch can also be useful.
If the weeds are growing in the lawn, then any broadleaf herbicide will work. But improving the overall health of the lawn through proper cultural practices (mowing height, watering, fertilization) is the first step.
This looks more like purple mustard? But it's definitely a type of mustard, which both hoary cress and purple mustard are.
It looks like this is in landscape beds and not the lawn? The biggest thing would be to make sure the weeds don't go to seed to break the seed production cycle. So mowing them now is helpful. It's a winter annual, so it will germinate in late winter/early spring and go to flower and seed before it gets too hot.
If you want to use an herbicide, anything non-selective will work - this could be glyphosate, organic "burn down" products, horticulture vinegar, etc. Lawn weed control products are not legally labeled to use in landscape beds.
Using mulch can also be useful.
If the weeds are growing in the lawn, then any broadleaf herbicide will work. But improving the overall health of the lawn through proper cultural practices (mowing height, watering, fertilization) is the first step.
I have tried the yard vinegar, 30 strength. Other than wilting the foliage, it didn't help. It is worse this year than last. Would Metsulfuron (ExportXP). Is that an herbicide you would recommend?
TY,
Mandy
No, that herbicide can only be used in the lawn, not landscape beds.
Hort vinegar often takes multiple applications - it's a burn down, so the plants regrow by the roots. It will work...but it will take multiple applications.
Adjust your cultural practices to make it more difficult for the weeds to grow....use mulch to smother the plants. The weeds are germinating in the rocks.
Hort vinegar often takes multiple applications - it's a burn down, so the plants regrow by the roots. It will work...but it will take multiple applications.
Adjust your cultural practices to make it more difficult for the weeds to grow....use mulch to smother the plants. The weeds are germinating in the rocks.
Thank you for the information. Are the herbicides you recommend (other than the Hort Vinegar) safe for dogs? On your suggestion of mulch, are you suggesting something like pine bark mulch? I have been careful not to use dried tree mulch because of the drought. That is why I put down squeegee rock mulch. I know it that area it is not thick enough, but do you believe the natural pine-like mulch would work better?
Thanks again,
Mandy
You'll want to read the label of any product you apply, but typically dogs can return to the area after the product has dried - but follow the label instructions.
All mulch, whether it's rock or wood, needs to be at least 3-4" thick to be effective against weeds. Bark mulch can be used, but if you're in a fire prone area, do not use it within five feet of any structure.
And as an FYI, horticulture vinegar is extremely dangerous and caustic. It has a "danger" label and you should wear full PPE and a respirator when using it. Few other herbicides available to homeowner carry a danger label. Organic doesn't mean that it's safe. Vinegar doesn't mean it's safe. It's acetic acid.
Or mow the weeds down. They are very large and herbicides will not work as well. Your best timing is when they are small and just germinating.
All mulch, whether it's rock or wood, needs to be at least 3-4" thick to be effective against weeds. Bark mulch can be used, but if you're in a fire prone area, do not use it within five feet of any structure.
And as an FYI, horticulture vinegar is extremely dangerous and caustic. It has a "danger" label and you should wear full PPE and a respirator when using it. Few other herbicides available to homeowner carry a danger label. Organic doesn't mean that it's safe. Vinegar doesn't mean it's safe. It's acetic acid.
Or mow the weeds down. They are very large and herbicides will not work as well. Your best timing is when they are small and just germinating.
Thank you for all the information. I do appreciate your help and the work you guys do to make Fort Collins a better place. I value it, and it is one of the reasons I moved here.
Mandy
