When should I prune grasses?

A Guide to Pruning Grasses

How to Care For Ornamental Grass The most common question we are approached with at this time of the year is what to do with ornamental grasses.  They add spectacular texture and form to the winter garden but eventually hit the point when they are far more messy than magnificent.

Many of us have the large, dormant grasses that we can just tie up, pull out the hedge trimmers and cut down.  For a handful of grasses though, this can cause more harm than good.  Here is a list of those grasses that are commonly used in St. Louis and the proper way to prune them.

Maiden Grass
Maiden Grass (Miscanthus)
Fountain Grass (Pennisetum)
Switchgrass (Panicum)
Maiden Grass, Fountain Grass and Switchgrass all go dormant in the winter, which means they will turn brown at the start of cold temperatures.  These grasses send up new growth every spring so they benefit by being trimmed back to keep their appearance clean and neat the following season.  However, while you can prune them back anywhere from late fall to early spring these grasses also add great texture to a winter garden that you may miss if you cut them back too early.When you finally trim them, cut Fountain Grass back to around 3″-4″, Maiden Grass and Switchgrass back to around 6″.  Cutting them back farther allows moisture to the crown of the plant (the plant crown is where the plant stem meets the roots) which can cause the grass to rot and die.  If you are uncertain of where the crown is, it is always better to leave an extra couple of inches.Lilyturf / Monkey Grass (Liriope)
Sedge (Carex)
Blue Fescue (Festuca)
These grasses fall under the small and stays evergreen category.  This means that by the end of the growing season enough brown foliage will be mixed with the evergreen foliage giving them a messy appearance.  The easiest way to clean up these plants is to put on your garden gloves and run your fingers through the foliage, effectively pulling out the dead and unsightly foliage.

Of course if a much more aggressive action is needed to rejuvenate your evergreen grasses then you can trim them back.  This should be done early to mid-spring using hand pruners and trimming the height back by two-thirds.  Within a few months after pruning these grasses will bounce back and look as good as new.  Cutting off the foliage of these grasses though causes the plant to lose energy that is stored in its leaves therefore they should only have a major pruning every 2 to 3 years.

Yucca (Yucca)
While technically not a grass, Yuccas are becoming more common in the St. Louis region and while they are easy to grow it is somewhat confusing on how to maintain them.  Typically Yuccas only need to be cleaned up, this can be done by taking the old or damaged leaves and pruning them back to the ground.  If your Yucca is in need of complete rejuvenation, you can prune it back to about 1 foot mid-spring.  It will take around 4 months for the plant to grow out of its haircut.