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Caring for Ornamental Grasses

The two most common questions we get about Ornamental grasses are "When should I cut my grass back" and "How and when should I divide my ornamental grass?" This article goes through tips and techniques on cutting back and dividing grasses.

Contributors: Kerry Meyer

The two most common questions we get about Ornamental grasses are "When should I cut my grass back" and "How and when should I divide my ornamental grass?" This article goes through tips and techniques on cutting back and dividing grasses.

In recent years interest and use of ornamental grasses has exploded. Ornamental grasses can fit into almost any garden theme. Ornamental grasses lend height, movement, and long season color to the landscape. Along with the proliferation of ornamental grasses have come a host of questions on how to care for them properly. Our two most common questions are "Do I need to trim my grass back and if so when?" and "How and when should I divide my ornamental grass?" We will give you some general rules to follow when cutting back and dividing ornamental grasses.

Grasses are generally classified as cool season, warm season, or evergreen. The rules change just slightly depending on which type of grass you have. Cool-season grasses put on most of their growth in spring before temperatures begin exceeding 75 degrees Fahrenheit and in the fall when temperatures cool down. They generally maintain good color through the summer but won't grow much when it is hot. Warm-season grasses won't start growing until mid to late spring or even early summer. Their major growth and flowering happens when the weather is hot. They will usually turn shades of brown for the winter. Evergreen grasses are usually plants that look like grasses but aren't actually classified as grasses. Plants like the sedges and carex are grass-like but not grasses.

I love rules of thumb, they make life much simpler than it would otherwise be. They help make sense out of the clutter of specific information. I found ornamental grasses rather confusing until I realized that there are a few rules of thumb that pertain to most of the grasses.

First Ornamental Grass Rule of Thumb: Cut back warm season grasses in fall or by mid to late spring.

Warm season grasses turn shades of brown as the weather turns colder. Once your warm season grasses turn brown you can trim them back at almost any time. If you like to tidy your garden in fall or if you live in an area where fire can be problematic trim warm season grasses so they are just a few inches tall. If you live in an area where fire generally isn't a problem you can leave the dried grasses and seed heads in your garden for winter interest. Snow or ice encrusted ornamental grasses can be quite beautiful. If you leave the trimming until spring try to make sure to cut them back to the ground (you can leave a couple of inches) by late spring, before new growth begins. Not all ornamental grasses look good through the winter, trim back those that don't look good in the fall.

Second Ornamental Grass Rule of Thumb: Cut back cool season grasses in very early spring.

Cool season grasses tend to look good even as the weather cools. Leave their foliage in place until spring and then as soon as the snow is gone cut them back. Leave about 1/3 of the plant in place. Trimming cool season grasses too harshly can irreparably harm the plant.

Now you know when, in general, to cut back ornamental grasses. However, how are you supposed to accomplish this? First find a good pair of gloves, thick leather gloves are probably best. Some ornamental grasses can have very sharp edges. For smaller grasses a pair of pruning shears will probably be sufficient. Trim about 2/3 of the plant for cool season grasses. For many grasses it is easier to tie the grass in a bundle before trimming, this makes clean up a snap. For short grasses this might not be possible.

If you have a large, established clump of grass, pruning shears probably aren't going to be enough and gloves become essential. You may need to use a weed eater (use one with a blade rather than string), electric or gas powered hedge trimmers, or even a chain saw. Once again, tie the tops together for easier clean up, just toss the bundles in to your compost pile. If you have only one of these large grasses you can cut them back with pruning shears but it isn't easy. I know. I've done it!

Dividing grasses is one way to increase the number of plants without spending additional money. Occasional division will help grasses remain active and growing and can help renew older grasses. Some grasses, over time, will die out in the center and dividing will rejuvenate the clump.

Third Ornamental Grass Rule of Thumb: Divide warm season grasses anytime spring through mid-summer.

All ornamental grasses should be divided when they are actively growing but not while they are flowering. If the plants are dormant when they are transplanted they won't establish a good root system. Warm season grasses generally start growing in late spring or early summer and have their active growth period during the heat of the summer. Warm season grasses will tend to bloom in mid to late summer.

Fourth Ornamental Grass Rule of Thumb: Divide cool season grasses in spring or early fall.

Cool season grasses are actively growing in spring and fall. These grasses can be transplanted at either time of the year but early spring is probably the best time to divide. If you do divide them in the fall, be careful that the freeze/thaw cycles of winter don't heave the plants out of the ground, this happened to a couple of my coral bells last winter.

Fifth Ornamental Grass Rule of Thumb: Divide evergreen grasses and grass-like plants in spring only

Evergreen grasses don't ever go dormant. Dividing plants wounds them to some degree. For evergreen grasses this wounding will really affect their ability to live through the winter.

How exactly do you divide a grass? For smaller grasses it is very similar to dividing a perennial. You dig up the grass clump and then use your hands, a pair of pruning shears, a knife, or a sharp shovel or trowel to cut or pull the clump into several pieces. Make sure that each piece has some roots. Replant them before the roots dry out, you may need to cover the exposed roots to protect them on sunny days. Just a reminder that grass leaves can be very sharp, wear gloves to protect your hands. I can tell you from personal experience grass cuts can really hurt.

Larger grasses use the same basic principles but due to shear size and toughness can be harder to deal with. It can take a strong back, or three, to get some of these very large grasses out of the ground. Dig and/or pry the clump out of the ground (don't be afraid of using a crow or pry bar) and then divide it into pieces, making sure each piece has some roots. An old hand or hack saw, an axe or hatchet (it may be easier to place the axe blade in one spot and then pound it through the grass clump using a large hammer or maul, I know I can never hit the same spot twice when swinging an axe), a very sharp shovel, a reciprocating or concrete saw, or a chain saw (this won't be gentle on your grass and will tear it up a bit, a chain saw should be your last resort) can all be used to divide the plant into pieces. These big grasses are quite tough.

An alternate method would be to cut the grass to the ground then use an axe or other tool to cut it into wedges. Pry or dig the pieces out of the ground. Once these larger pieces are removed from the ground you can cut them into smaller pieces using sharp pruning shears.

If your main clump is still looking quite healthy and hasn't outgrown its space, you can replicate the plant by removing small chunks of the grass from around the outer edge. This may be easier than dividing the entire plant.

Once you have the pieces removed from the main clump, trim off any dead material, replant the pieces, and water thoroughly. Newly divided grasses will need frequent watering while they become established. Once they are well rooted you should be able to decrease or quit watering.

Now that you've pried a monster from the ground, chopped it up into little pieces and planted the pieces all over the yard. Sit down with a cool glass of lemonade and bribe your spouse or a friend into rubbing those aching muscles!

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Anonymous's picture
Anonymous Tue, 04/26/2016 - 2:19pm

Can more than one piece of a divided ornamental grass be planted in the same hole to create a larger plant?
Or should the divided pieces always be used to create individual plants?

Kerry Meyer's picture
Kerry Meyer Tue, 05/24/2016 - 10:02am

Yes, you can put more than one piece of the divided grass in the same hole so that the plant starts out larger.  It might be a bit easier if you simply left larger pieces when you divide the plant, rather than using more than one in a hole.  But either should work fine.

Anonymous's picture
Anonymous Wed, 04/13/2016 - 5:58pm

Thanks for your article. I just divided at 5 foot diameter ornamental grass into quarters to replant.

Do I need to "shape up" the plantings or just leave them wedge-shaped? Does it matter?

The original plant grew to six feet tall every year. Any idea how tall the new plantings will get this year?

How long will it take for the new ones to look like their momma which was planted by previous owners eighteen years ago?

Thanks for your help. Ann

Kerry Meyer's picture
Kerry Meyer Mon, 04/25/2016 - 4:08pm

I really don't think you need to trim them up, but doing so might help the fiinal plants look more symmetrical, so depending on how important that is to you, you can leave them or shape as desired. 

I would expect their height to be pretty similar to the original plant this year.  Most Ornamental grasses come back froom the roots each season so there is no reason to believe the height won't be similar as it has been in the past.

It will take a while for them to slowly grow in diameter...

Kerry Meyer
Proven Winners

Anonymous's picture
Anonymous Sat, 10/17/2015 - 4:31pm

We have a 2nd home in Moab, UT and planted a lot of ornamental grasses. Two varieties are Karl Forester and Heavy Metal but i can't recall the names of the others. We absolutely love them; they add so much to the interest of our yard. My s
problem is they are on a drip in berms mixed with high water plants so the grasses have gotten enormous and are choking out the other perennials. Is it too late to dig them up and thin (divide) them now? One variety has started turning brown. Thank you!

Anonymous's picture
Anonymous Sat, 10/10/2015 - 10:08am

I have five containers with a different grass in each pot sitting on my deck. They were planted in April and have flourished!
Now that winter is coming what do I do to protect them, I know you cut them down in spring but what to do to winterized them.

Sandy Wentworth's picture
Sandy Wentworth Mon, 10/12/2015 - 11:17am

This depends if they are annual grasses or perennial grasses and what state you are in.

If they are perennial grasses it is too late in the season to plant them so they can be kept in a shed or garage watering once a month.

Annual grasses would need to be kept inside, they get messy and still go dormate so they can get unsightly.

Sandy Wentworth

Anonymous's picture
Anonymous Sun, 09/27/2015 - 3:39pm

I don't have a good place to dispose of lawn waste.
Will ornamental grasses die if not cut back yearly?

Kerry Meyer's picture
Kerry Meyer Mon, 09/28/2015 - 5:02pm

They won't die, they'll just have a tendency to look unsightly.  The yearly clean up (evergreen types are the exceptions) keeps them looking more tidy and increases ornamental value.

Kerry Meyer
Proven Winners

Anonymous's picture
Anonymous Wed, 08/26/2015 - 11:02pm

I inherited about 20 grasses that were watered regularly, but are brown from being left in their original nursery containers all summer. The roots seem okay and there are a few green blades. Will they survive if I plant them now? If so, how should I plant them and care for them to give them the best odds? Thanks so much for your expertise!

Kerry Meyer's picture
Kerry Meyer Thu, 08/27/2015 - 1:37pm

If they are green and growing and you transplant them now they should be fine.  Make sure you loosen the soil around where you are planting each grass, this will it easier for roots to get established in the landscape. Also, make sure that you keep them well-hydrated, especially while the weather is hot.  Once it cools off, be sure you don't over-water.  Early in fall is a great time to plant perennials, shrubs, trees and grasses.  Annuals that can take a hard frost (violas, pansies, osteospermum, diascia, nemesia, argyranthemum to name a few) will bloom for weeks or in some cases months.

Anonymous's picture
Anonymous Sun, 08/02/2015 - 5:26pm

i bought a house in late spring and the grasses weren't cut back. Now they're getting pretty big for the space and have seeded. Do I need to wait until September/October to cut the, back? Thanks!!

Kerry Meyer's picture
Kerry Meyer Mon, 08/03/2015 - 3:03pm

It would be best if you can wait to cut them back hard until fall.  However, some trimming to keep them looking tidy or to not allow them to overtake neighbors is fine.  Just don't cut them back to the ground, if you can help it.  They might be OK in the end, but it would be really stressful for them.


Anonymous's picture
Anonymous Sat, 07/25/2015 - 1:33pm

I planted several Avalanche grasses about a month ago. They get afternoon sun only. I water them whenever the ground seems dry. They haven't grown at all. Before I planted these, I had planted Overdam in the same spot and in 10 weeks time there was very minimal growth. Is this normal? Can I expect full growth eventually? I live in South Dakota.

Kerry Meyer's picture
Kerry Meyer Mon, 08/03/2015 - 3:05pm

I would say this is pretty normal especially since you planted them in summer.  The plants are putting their energy into growing roots instead of shoots at this time.  I wouldn't be surprised if they don't seem to change much this summer, but take off next spring.

Anonymous's picture
Anonymous Mon, 07/06/2015 - 11:19am

I really like this article.
What would have been really helpful, is if you would have also written the names of some cool season grasses, warm season grasses, evergreen grasses, and Sedges, etc. that look like grasses, but aren't truly a grass. I bought a house that has some grasses that I'm not sure of which type they are, when and how to trim them, or how to best divide them. If I had some names of ornamental grasses & sedges, I could look them up and find out what mine are for certain so that I am treating them the best possible.
This spring, I cut back an evergreen grass, probably by too much because it is most definitely, "Wounded" from it now.
Thank you.

Kerry Meyer's picture
Kerry Meyer Tue, 07/07/2015 - 2:24pm

Thank you for the suggesion.  We include the classification neutral/warm season/cool season information within each of the grass records in our system.  However, adding them into the article would make sense too.


Anonymous's picture
Anonymous Sat, 06/06/2015 - 5:27pm

We split and transplanted a grass and it's growing but very slowly. Not like the others. Any suggestions??

Kerry Meyer's picture
Kerry Meyer Fri, 06/12/2015 - 9:50am

From your question, I think you are comparing the growth rate of a grass that was recently divided to ones that were not recently divided.  If that is the case, then it is not unexpected for a newly divided and transplanted grass to grow more slowly than those that weren't recently divided and transplanted.  The newly divided one is growing new roots in addition to top growth, because energy is divided between roots and shoots, it is growing more slowly.


Anonymous's picture
Anonymous Fri, 08/17/2012 - 3:04pm

I've found that rather than cutting back by making a flat cut level with the ground, that if I cut the grass in a pineapple or pinecone shape, the new growth blends in better.

Anonymous's picture
Anonymous Thu, 04/05/2012 - 6:43am

If you dig the center out of older grass it will keep its shape & grow back with renewed vigor.

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