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Commonly Asked Questions about Growing Ornamental Grasses

When ornamental grasses are in their prime in landscapes across North America each fall, questions pour in to our feedback line. Do you have a question about grasses, too? Here’s a list of the ten most commonly asked questions about their traits, uses and growing conditions.

Contributors: Susan Martin

Q: Are the grasses I see blooming in gardens this time of year perennials?

A: Most of the grasses you notice blooming in landscapes this time of year are perennials, meaning they will come back again next year. They can really enhance the structure, height and movement in a garden’s design. But to know for sure if a grass is an annual or perennial in your area, you’ll need to identify which variety it is.

Perennial grasses are ones that return on their own each year, so you only need to plant them once. An example of a hardy perennial grass is Prairie Winds® ‘Cheyenne Sky’ switch grass, pictured here. They make popular landscape plants because they are easy to grow and maintain, and mix well with many kinds of shrubs and perennials. See our whole collection of perennial grasses here.

Annual grasses can be planted in landscapes too, but more often they are grown in containers since they only last one season in most climates.
If you like them, you can replant them every year. Many annual grasses make dynamic “thrillers” in combination containers like the one you see here featuring Graceful Grasses® ‘Fireworks’ red fountain grass. See our whole collection of annual grasses here.

 

 

 

 

Q: How should I incorporate ornamental grasses into my garden? 

A: As a home gardener, you might find it easy to decide where to plant a new hydrangea or set a pretty pot of annual flowers, but figuring out where to use ornamental grasses can be a bit more challenging. Plopping one down in the middle of your flower bed might look out of place, but add a few more by its side and it all starts to come together. We’ve put together this article showing five ways to use grasses in your garden including:

  1. As a focal point
  2. As a fall accent
  3. In the mixed border
  4. As a living screen
  5. In water gardens

 

 

Q: When is the best time to plant new ornamental grasses in my garden?

 

A: The best time to plant new ornamental grasses in your landscape is spring or early fall. Planting before the summer’s heat (and often dry weather) arrives should give them enough time to root in before having to endure more stressful conditions. It can be tough to keep them watered well enough if planted in summer, so if you miss the spring window, aim to plant in early fall at least 6-8 weeks before the first frost.

 

 

  

Q: When is the best time to divide the grasses I already have growing in my garden?

A: Ornamental grasses are generally divided into two groups: warm season grasses which grow and bloom in the warmer summer and fall months, and cool season grasses which grow and bloom in the cooler months of spring to early summer. If the grass you have blooming in your garden started to put up its showy plumes or seed heads in late summer to early fall, it’s a warm season grass. If it bloomed much earlier in the year, it’s a cool season grass.  

Warm Season Grasses to divide in spring to early summer: Juncus, Panicum, Pennisetum, Schizachyrium

Cool Season Grasses to divide in spring or early fall: Carex

*Evergreen grasses and plants that look like grasses but aren’t classified as “true grasses” such as Cyperus and Scirpus should only be divided in spring if necessary.

Warm Season Grasses -
Click the image to see the varieties pictured above. 

Cool Season Grasses -
Click the image to see the varieties pictured above.

 

Q: How often should I divide the perennial grasses I have in my garden?

A: Perennial grasses like Panicum and Pennisetum tend to bulk up fairly quickly in the landscape, so you can safely divide them every 3-4 years. Schizachyrium tends to grow more slowly, so it will need dividing less often.

You’ll know it is time to divide your ornamental grasses when you see fresh leaves coming up out of the outer ring of the clump in spring, but there is a dead spot in the center. This is a perfectly normal occurrence. Dig up the entire clump, use a saw or sharp knife to chop the rootball into pieces at least the size of a large grapefruit, and discard the old, woody center. Replant one piece in the original spot and move the others to another place in the yard or give them away to a friend. 

It’s better to divide grasses more often than not enough. That’s because they develop a dense root system and anchor themselves strongly into the garden once established. If you let them go too long without dividing, you’ll need a backhoe or team of very strong individuals to dig them up. Better to keep them to a manageable size.

 

Q: What time of year should I cut back my ornamental grasses?

A: Perennial grasses that go completely dormant in winter like hardy fountain grass, switch grass and little bluestem can be safely cut back anytime between early winter to early spring. Timing is a matter of personal preference. Some people enjoy the visual interest and wildlife support they provide in winter, but others prefer to clean up the garden in fall so they can start fresh as soon as the snow melts in spring.

Perennial grasslike plants such as sedges and evergreen grasses rarely need pruning, but if you must, do so in spring. Remove any tattered foliage just before or as the new growth is beginning to appear, making sure to leave at least one third of the plant intact. These types of grasses don’t like to be pruned frequently

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Q: How far back should I cut my grasses?

A: When you are ready to cut down your dormant perennial grasses, grab some gloves, a bungee cord, and a saw, electric hedge trimmer or sharp pair of pruners. Start by tying up the clump with your bungee cord. This will make it easier to reach the base of the plant where you’re about to cut and will make disposing of the bundle of cut stems much easier, too. Cut the foliage down to about 6 inches off the ground.

Remember, grasslike plants such as sedges and evergreen grasses don’t like to be pruned frequently. If you must prune them, do so in spring and make sure to leave at least one third of the plant intact.

 

 

Q: Do ornamental grasses need to be fed?

A: Many ornamental grasses are selections of native prairie or woodland plants. In their natural habitat, the only nutrients they receive comes from their own decomposing foliage and that of the plants around them. You can mimic those conditions by mulching around the base of your grasses in fall with shredded leaves. No other fertilizer is needed or desired by grasses; in fact, feeding them often causes them to stretch and flop over.

 

 

Q: Are ornamental grasses drought tolerant?

A: Just like how some annuals and perennials don’t need much water to grow, some ornamental grasses are drought tolerant, too. It depends on the type of grass. To know if the one you’re growing is drought tolerant, you first need to identify what kind of grass it is.

Native prairie grasses like Panicum and Schizachyrium are quite drought tolerant and in most cases, can easily survive without much supplemental water.

Annual and perennial types of Pennisetum are not drought tolerant. They do not like the soil to dry out, but don’t like soggy wet soil either. Aim to provide average moisture, meaning not too wet and not too dry. You’ll know the soil is too dry if the tips of the leaves turn brown. While that won’t be as noticeable on green leaved varieties, it will be very obvious on those with dark purple or red foliage.

Some grasslike plants like Cyperus and Scirpus are water lovers—in fact, they can even grow in standing water. They can handle average moisture in garden beds and containers, but they will really put on a show if you give them a drink frequently.    

 

 

Q: Do birds and other critters like ornamental grasses?

A: If you ever get out to the country or do any hiking, you know that grasses are found are everywhere in nature. They are part of the natural ecosystem and coexist peacefully with birds, pollinators and other four-legged creatures.

Birds often use grasses for nesting material in spring and eat their seeds in fall and winter. The main role grasses play in nature is to provide a protective place for critters to hide, nest or burrow. Deer don’t typically munch on them, but rabbits might when the foliage is first emerging in spring. This usually isn’t a problem because the grass quickly outgrows their reach.  

 

Have more questions about ornamental grasses?

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