Pruning Ornamental Grasses
Allen Robinson: Ask a
Master Gardener
Tuesday, January 30,
2018
Q: When is the best
time to cut down my ornamental grasses? And, I have a lot of it, so what’s the
best way to prune them? Angela W., Tulsa
A: Grasses and grass-like
ornamentals are great resources for gardens and landscapes. Whatever the garden
need, there is likely a grass to offer a solution. They come in all sizes, from
a few inches to more than 10 feet tall, and may be annual, perennial, evergreen
or deciduous. The spectrum of colors, leaf patterns and textures will provide
something to please most any gardener.
Many of the true
grasses have intriguing fall colors and evolve to an earthy tan color for
winter. So for most of them, like the large Pampas Grass, the show is not over
in the wintertime. They have large decorative flowers and seed heads that catch
the breeze, which adds movement and sound to the winter landscape. They not
only provide interesting landscape, but also valuable shelter from the weather
for birds. These seed structures can also be of value to use indoors for
long-lasting floral arrangements.
For new growth to
emerge in the spring, the old stems should be cut to a height of a few inches
in late winter. Do this before new growth begins. If you wait too long to trim
in the spring after new leaves emerge, you will remove the tops of new growth.
Cutting back allows needed air and sunlight to get into the root zone and
provides room for new growth. The stems on these grasses are substantial and,
in many cases, can be difficult to cut. The use of a power hedge trimmer seems
to be most effective for the larger grasses, such as Pampas and Zebra grass.
As for small
ornamental grasses, Liriope is one of the most common grasses around but is
actually not a grass at all. It is of the lily family from Asia. The many
varieties available are durable and tolerant of most soils. One of their
greatest assets is shade tolerance. They do well in partial to deep shade and
will get sunburn in full sun.
These plants are not
perennial but are evergreen and retain their usual color throughout the winter.
Be aware that both tend to get a fungus called anthracnose, which causes brown
spots. By the end of winter, they usually are looking a bit ragged but then
predictably send up a flush of new growth in the spring, so late winter
trimming is also needed.
Because the total
height of these is less than a foot, lawnmowers or weed eaters are useful for
removal of old growth. Cut the leaves down to 3 inches or so and discard the
old leaves if they are showing any signs of fungal growth.
Pruning time is also a
good time to consider dividing the grasses. This needs to be done every three
to four years. Doing so will help to maintain vigor and to prevent disease in
the central root area.
Garden
tips
- Begin planting blackberries,
raspberries, strawberries, grapes, asparagus and other perennial garden
crops in February.
- One can continue in the month
of February spot-spraying weeds in your dormant Bermuda lawn. Use a
product containing glyphosate. Use when the temperature is above 50
degrees. Read the label carefully before using.
- Tomato seeds are best planted
in indoor flats around Valentine's Day for mid-April garden transplants.
Should you decide to grow your own tomato transplants from seeds, consult
OSU fact sheet “Growing Tomatoes in the Home Garden,” which can be found
on the Tulsa Master Gardener website at tulsamastergardeners.org. In that
same section of the website, you will find additional fact sheets on
growing conditions, pests and diseases, which are helpful.
