It would help to know what variety your grasses are, as there are different times and methods for different varieties.

In general, I divide grasses at the same time I give them their annual haircuts. Cool season grasses get done in late winter and warm season grasses in early to mid-spring.

Again in general, the method is to shear the grass back, and then dig up the clump. I cut the clump in quarters, and cut off and discard the center point of each , because the younger and more vigorous growth tends to be on the outer perimeter of the plant.

It's best to have the new planting location prepared in advance, so you can immediately re-plant the divisions.

If your plant is to be divided into many small plants, I find it better to rinse the old soil off the roots. Then I use a sharp knife to cut the size divisions I want. Watch for old and dead roots, and avoid them. When cleaned of soil, it's pretty easy to differentiate between new growth and old. Chunks as small as 1-2" square will grow into healthy plants quickly.

Don't be afraid of hurting these guys. Grasses are extremely tough plants.

Thanks donn!

This is exactly the information I needed - and in the detail I need.

I'll follow your instructions in the spring!

Donn

After spliting the grass, what kind of growth rate is there.. I have a 8 ft specimen that I will be splitting into quarters...will i get four 8ft, but thin, specimens?

Tom

Hi Tom,

If your grass is hitting 8' now, it'll probably take a couple of years for it to return to that height. The division process reduces the overall root mass of each new division, and a plant's visible structure is determined by it's root structure. As the root mass re-develops, the maturity, fullness and height of the above-ground structure will increase.

This, of course, depends very much on the nature of the grass you're dividing. If it's mature form is columnar (tall and thin) like Panicum virgatum 'Northwind' then the divisions will be the same way, just not quite as tall at first.

There was a very informative AND amusing thread on this subject back in 2007. It even included comments on which tools to use.
A quick search turns it up.

Here is a link that might be useful: Dividing Grasses