How to divide Ornamental Grass

Most species of Ornamental Grass that are grown in the garden are clump-forming with fibrous roots. Over time, the base clumps of these grasses will increase in diameter. Eventually, after 3-5 years these clumps will grow so large that the centers will die out. Once this occurs, the ornamental grass will start to look sickly. So, in order to keep the grass plant looking healthy and vigorous you should divide the base clump. In a nutshell, you are just going to dig up the entire clump, then cut the clump in half using a shovel, saw or knife. This process is very similar to how you can divide other perennial flowers.

Big Bluestem Andropogon gerardii — Big Bluestem Blooming

How to determine if you need to divide your Ornamental Grass?

In general, Ornamental Grasses should be divided every 3rd year. Or, if the center of the clump doesn’t appear to be making any new growth. If the center of the clump looks dead, then you should divide the plant. So, if you see all of your plants ‘waking up’ from the winter, examine your ornamental grasses. If you see new growth around the plant, but none in the center it may be time to divide.

When should you divide your Ornamental Grass? Or, what time of year should you divide roots of grasses?

The best time to divide ornamental grasses is early in the Spring while temperatures are still cool. Because of the cool temperatures there will not be a heat load on the plant, which means that it won’t require as much water. Furthermore, the soil tends to stay more moist in the Spring. Also, the grass will still be dormant. Being nearly dormant means that there won’t be as much shock to the ornamental grass when it is cut in half!

I like to do this every second or third year on my Big Bluestem and Little Bluestem grasses.

Tools and Materials required for dividing ornamental grass

Garden Sheers or Clippers
Shovel or Spade
Camping saw, bow saw, or gardening knife
Trowel
Top soil or potting soil for back fill
Watering can

Step by Step Guide to dividing Ornamental Grass with Pictures

Water the ground thoroughly. The day before you want to divide/transplant your ornamental grass, you should heavily water the ground. Moist soil will make digging out the clump much easier.
Cut back the dead grass from the previous year. Locate your grass, and trim off the excess growth with clippers.
Locate the entire Clump of Grass. Clear away any mulch or leaf litter from the base of the plant. You want to make sure you can identify the entire clump.
Dig out the entire clump of grass. Take your shovel and place it 2-4″ away from the clump. Angle it at 30-45 degrees from vertical, and push it towards the center of the clump. Then, gently rock the shove handle down to loosen the clump. Repeat this step all the way around the outside of the clump.
Remove the clump from the hole. Then, stab the shovel one more time, getting under the entire clump. You should be able to lift or pry up the entire clump. If the clump is very large (3′ or 1 m in diameter), you can just verify that it is loose in the hole, then lower it back into the hole. We can divide it inside it’s hole.
Ignore the white line! My camera put this on, and I’m not sure why!
Depending how large it is, you now need to carefully split it in half, or into four equal parts. Replant one of the original clumps in the hole, using some top soil or potting soil as backfill. Another optional step that helps is to add a bit of compost into the hole when you add your back fill. No need to go crazy, just 1 – 3 handfuls will be sufficient.
Plant, or give away the other clumps!
Water all clumps that have been replanted. Monitor the grasses to ensure adequate supply of water.