I have a strip of dwarf mondo grass down the middle of my driveway. Pennywort has started to grow in amongst it, and is gradually spreading and taking over.

I have tried manually weeding it out (was spending 10 or 15 minutes each day), however it's coming back as fast as I can remove it. Because of the mondo grass roots, it's very difficult to get all the pennywort roots out.

The mondo grass is growing quite well in areas the pennywort hasn't reached yet.

Is there anything I can do? Can I change the conditions to suit the mondo grass more than the pennywort and give it a better chance?

I don't mind using a herbicide if required. I'm not much of a gardener so any help is appreciated.

Pennywort in mondo grass

  • when you are removing by hand, are you doing so after a good downpour or good soaking with the garden hose? Sorry if this is teaching you to suck eggs, but pulling weeds cleanly out of the ground is a lot easier when the soil is nice & wet.
    – Mike Perry
    Commented Jul 16, 2011 at 4:49
  • Also how do you feel about the use of selective herbicides or do you favour and organic approach?
    – Mike Perry
    Commented Jul 16, 2011 at 4:51
  • If it helps others, this is one of two weeds known as 'Dollar Weed'. It is creeping with thin spindly side shoots. For physical removal you have to get these and their tiny root clumps. Lawn weedkiller might be worth a try but I've faved the question as I am interested in an effective answer.
    – winwaed
    Commented Jul 16, 2011 at 13:24
  • I gave up on this, pulled everything out and replaced with rocks.
    – WW01
    Commented Jul 10, 2020 at 8:03

3 Answers 3


Q. Can I change the conditions to suit the mondo grass more than the pennywort and give it a better chance?

A. Mondo grass (is an Ornamental grass, this is important for the herbicide part of the answer), prefers a moist soil. Pennywort thrives in wet soils. Therefore if you can reduce the moisture level in your soil you will (to some extent) hit negatively the Pennywort and improve the conditions for the Mondo grass.

  • Improve drainage by amending the soil appropriately. Example, usually that involves adding organic matter to your soil - stuff like compost, finely shredded Autumn "Fall" leaves, well rotted farmyard manure, etc. If your soil is more like clay, adding some coarse sand and fine crushed rock can be worthwhile (along with the organic matter)..
  • Water less (obviously you can't turn off the rain).

Q. I don't mind using a herbicide if required. I'm not much of a gardener so any help is appreciated.

A. From what I have read (links below), an "imazaquin" based selective herbicide can be used around some Ornamental grasses to help control/fight Pennywort. Of course before using such a selective herbicide you would need to read the label (or contact the manufacturer directly) to see if it's safe to use around Mondo grass.

  • 1
    +1 I'd also add that it would be useful (even after reading the label) to spot-test the herbicide to make sure it doesn't injure the Mondo and that it kills the Pennywort.
    – bstpierre
    Commented Jul 16, 2011 at 21:47
  • 2
    After about 3 weeks of no rainfall (and no watering) the pennywort was starting to shrivel. Perhaps it may have died, but now it's raining again. It appears more sensitive to lack of water than the mondo grass so will try to kill it that way as we move into summer here.
    – WW01
    Commented Oct 2, 2011 at 8:41
  • @WW01 Thanks for the update & good luck controlling (removing) the Pennywort via lack of water (moisture).
    – Mike Perry
    Commented Oct 2, 2011 at 13:55

You can make up a small amount of general weedkiller in a jar and remember to wear gloves and not to get it on your mondo grass.

Use a small paint brush and paint the weeds with the weedkiller. Watch out for drops. You can put a small amount of dye in the mix so that you can see were you have been but not too much or it might react with the weedkiller.


You can't get rid of this crap unless you are in for the long haul. I've read every article on the web from tilling to weed killers. I have tilled my garden boxes 4xs sprayed, you named it I have done it. Pulling by hand multiple times a week, yes I said week. It seems like for every bunch I pull 50 more grow in its place. Their roots go so deep you have to go down 12 inches sometimes, not to mention their long and thick. I have been gardening for the last 5 years never had a problem, plant the same thing, never over-water, so I'm baffled.

This is what I have been doing that seems to be keeping these little suckers in check. I tilled the outside perimeter. Sprayed weed and grass killer ( spectricide) waited 3 days then sprayed weed killer for lawns. Oh and last but not least you must get every take a hand rake and constantly disturb new roots and rip them out by hand. Good luck.

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