All ornamental grasses benefit from an annual pruning in late winter or early spring, before new growth begins. Why not in the fall? Ornamental grasses add so much winter interest to your landscape that it pays to wait. Let those grasses work their winter magic and then prune. Removing the dried biomass in early spring allows new leaves and stems to emerge from the root mass without being blocked from essential sunlight by last year’s lifeless shafts. Don’t simply prune off the tops and flowers as some do. That does nothing to address the buildup of old foliage which is blocking sunlight.
Tall ornamental grass plants should be cut back to a height of 6 inches. Such pruning allows additional light to reach the center of the plant where the new shoots are emerging. The increased light increases the number of developing shoots and enables them to grow quickly. Some gardeners recommend cutting ornamental grasses all the way to the ground. Unfortunately, this can injure new shoots and allow moisture to gather on plant crowns and lead to rotting.
Make sure you prune before new shoots emerge. Those shoots can grow quickly. To check for new growth, pull back the dead grass and check the center of the clump at ground level. Avoid cutting any green shoots when you’re pruning away old growth.
Before pruning, wrap twine around the clump of dead grass and tie it into a bundle or use bungee cords. This will make pruning and clean up much easier. Choose a tool that will make a sharp clean cut. While pruning a few individual stems can be done with hand pruners, cutting the whole plant back requires a more powerful tool. Electric hedging shears work well for cutting large grasses down. Battery-powered hedging shears are also worth considering. While you may have found them lacking adequate power in the past, there’s a new generation of cordless hedging sheers which provide ample cutting power and can operate for up to an hour on each charge. These are perfect for grasses like maiden grass, feather reed grass and fountain grass. Again, simply tie or bungee your grass into a bundle and give it a crew cut.
Most ornamental grasses in our region are of the clumping variety. A clumping plant grows into a rounded clump of stems and leaves and broadens out in circumference each year. A rhizomatous ornamental grass spreads out through underground rhizomes or surface-running stolons. Clumping varieties are generally preferable as rhizomatous grasses tend to be invasive. Also, clumping varieties are generally easier to trim because the root mass is concentrated, literally clumped together.
The other important spring task involves rejuvenating or replacing dying plants. Most ornamental grasses start to look worn out after three to five years. Digging the plant up and dividing the root ball mass and replanting healthy sections provides new plants. Most ornamental grasses tend to wear out at the center, with healthy growth and roots at the periphery. The worn central section can be dug out and discarded and healthy sections taken from the periphery and transplanted into the center. Some gardeners simply cut out the central dead area and fill with compost, creating a temporary doughnut look. They claim the healthier grass around the center soon fills in the doughnut hole.
Of the low-growing ornamental grasses, blue fescue is a favorite in our region. Blue fescues should be sheared back annually to a few inches from the ground to allow room for fresh new foliage to grow. Blue fescues are considered as short-lived, because they eventually accumulate a mass of dead foliage if they aren’t pruned and divided every few years. I personally find digging up sections of a blue fescue more trouble than it’s worth. The root mass can be thick and dense, and the digging required to remove spent sections and replant healthy sections is daunting. I choose to simply dig up the old spent plant and put in a new one. If you don’t want to replace your blue fescues every 5 to 7 years, then I’d suggest pruning every year and dividing every 3 or 4 years.
One final pruning suggestion: Even on a sunny day, wear a long-sleeved shirt and gloves to prune your ornamental grass. Blades of grass and stems can and will cut your skin if you aren’t property protected. Also, trimming ornamental grasses can be messy. Spread plastic or a tarp under the plants to collect cuttings, making it easy to dispose of trimmings. Also consider putting down mulch when you’ve finished pruning to cover up anything the rake doesn’t pick up.
Garden Wise is presented by the Magic Valley Master Gardener Association. We will try to answer questions of general interest submitted by the community. Please submit questions to email@example.com.
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