Cutting ornamental grasses

Question:

We have maiden grass plants growing in our back yard, and there are many plumes on the plants. Should we cut them back during the winter? Please tell us what to do.

Alan C.

Answer:

You can cut the flower stalks of ornamental grass now if you wish, or you can leave them for landscape interest through the winter. If you are concerned with seed from your grass creating weed problems, remove the flower stalk now and dispose of it. If you want to feed birds through the winter, you can leave the flower stalk. Your ornamental grass, maiden grass (Miscanthus sinensis cv. Gracillimus) may not produce viable seeds. That means that it is probably not a problem with regard to spreading seeds to make weeds, but it also means that it is unlikely to provide food for the birds. It is really a matter of deciding what you want. Do you want the gracefully swaying seed heads to provide winter interest in your landscape? If not, you may prefer to remove them so that they do not distract from other plants in your landscape.

You didn't ask about cutting the leaves, so I wonder if you are concerned with the weed potential. The species Miscanthus sinensis has become a problem in moist regions of the country, but the ornamental cultivars are usually considered to be safe. This is because many of the cultivars may be sterile hybrids that do not form viable seeds. If you have seen seedlings resulting from viable seeds, then the concern regarding escaped plants is a valid concern. In New Mexico, this concern is greatest if you live near the river or irrigation ditches that will provide the water needed by this grass. In the more arid parts of the state, it is less likely to cause a problem unless you are close enough to waterways that the wind can carry the seed. In landscapes that are in arid portions of the state, it is sufficient to eliminate any seedlings that develop. It is important that we do not import weeds into the state as ornamentals. If you have seen seedlings developing, you may want to remove the plants that are producing the viable seeds and replace them with another variety that is truly sterile.

If you are also wondering when to cut down the foliage, you can do that now or wait until early spring.

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Transplant iris in winter?

Question:

Can I transplant my iris plants now? They have grown very vigorously and are taking over the flower bed!

Mike F.
Las Cruces

Answer:

If this is a new and expensive variety, you may choose to wait; otherwise, you can transplant them now. If you do transplant now, you may sacrifice the coming spring's flowering.

Irises should have been transplanted at the end of summer/fall to allow root growth and plant establishment before the onset of cold weather. However, irises are very vigorous and in your area will probably establish and grow even if transplanted now. They may even bloom.

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Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!