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Pampas Grass

..or is it Maiden Grass?

By: Sandy Feather 2009
Penn State Extension


Q. We have a rather large pampas grass plant. What is the best way to reduce its size?  In the past I have split it and given pieces away to be replanted by others.  However, that seems to make the remaining plant even larger the next growing season.

A. In correspondence with the writer, I suggested he dig up the entire plant, divide it up and replant a very small division. However, the plant has outgrown its allotted space and he has run out of people who want a piece of it - just like your neighbors start to hide from you when your zucchini plants are too productive! Now he just wants to know how to kill it.


Is it Pampas Grass or another type of ornamental grass?

I doubt that he really has pampas grass (Cortaderia spp.) because it is not generally considered winter hardy in our climate. Some varieties are hardy to USDA Zone 6, but most pampas grasses are only hardy to USDA Zone 8. It may be one of the maiden grasses (Miscanthus spp.) or Ravenna grass (Saccharum ravennae). Any of these can quickly outgrow its space in the garden. Most of our ornamental grasses are warm season grasses. They are best planted and/or divided in spring only; fall divisions often fail because they do not have time to become established before winter cold hits.

 


Removing ornamental grasses

Getting rid of an overgrown, well-established ornamental grass can be a chore. They usually have large root systems and are very difficult to dig up. Rather than trying to dig the entire clump up, you can dig it out piecemeal. If you leave many roots behind, they will probably re-sprout next spring. Just continue to dig the re-sprouts out, and eventually you will be rid of it.

clump of ornamental grass

It will be too late to spray by the time this article goes to press, but late summer-early fall applications of a non-selective herbicide such as Round Up (glyphosate) can be very effective. If you can find Roundup Pro or one of the 41 percent glyphosate knockoffs like Eraser (Agway), it would probably be more effective than the homeowner formulations you typically find at the big box stores. They are more likely to be available at a commercial turf and landscape or farm supply store.

Since glyphosate is non-selective, you must use it carefully to avoid getting any of the spray on desirable plants or lawn areas. It takes 10-14 days for glyphosate to work, so do not be discouraged if the grass does not die immediately after you spray it. Ornamental grasses are tough, and it might take more than one application to get rid of it for good.


Best time for chemical controls

Late summer-early fall is a good time to make herbicide applications to control perennial weeds and plants you want to get rid of because they are translocating the products of photosynthesis down to their roots for storage over the winter. They take the herbicide down to the roots quite readily too, resulting in more complete control. Spring applications are often not as effective because the movement of sap in the plants is up and out.
  

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