The best time to divide pampas grass is spring, but it may be better to replace it

The best time to divide pampas grass is spring, but it may be better to replace it

Pampas grass may soon be listed as an invasive plant. It can be divided, but this is a difficult chore. It would be easier to simply replace it with a different ornamental grass.

In the garden

s: I had a big pile of pampas grass that was probably 15 to 20 feet high, but the center was almost gone. I want to take it out to divide it and replant it. Should I do this in the winter or wait until spring?

a: As with all ornamental grasses, the best time to divide pampas grass (Cortaderia is crying) as soon as new growth appears in the spring.

Books describing how to divide pampas grass often recommend using a digging trowel to remove part of the side of the root ball. This will probably work if you divide the clump every three years, but the root ball of a huge old specimen like yours will be too thick and tangled to be divided with a spade.

If you really want to do this, the first line of action is to eat your Brussels sprouts to muster extra energy for this challenge. Then start cutting the grass blades as close to the ground as possible. Rent a suit of armor or wear heavy clothing when you try this. Thick, difficult-to-cut leaves have sharp edges.
Next, you will dig and lift the root ball to divide it, but it will be heavy, so you may want to enlist some sturdy helpers to help you. The best tool I've found for cutting the root ball is a good-sized bow saw.

Take a healthy portion from the side of the root ball. Make sure it has at least five buds and plenty of healthy roots. When replanting, choose a sunny location with well-drained soil, and add plenty of compost to the planting hole and surrounding area.

Or save yourself a lot of hard work by replacing this giant with a different type of ornamental grass, e.g Miscanthus sinensis “Gracelimus.” Pampas grass is monitored by the Washington State Noxious Weed Council and may soon be listed as an invasive plant, possibly requiring removal. Visit and click on “All Grasses” for a list of ornamental grasses that are not only incredibly beautiful, but also much easier to handle if they need to be divided.

s: I am new to the Northwest and am overwhelmed by the variety of evergreens and other plant species. Is there a book, field guide, or other source that identifies the species that grow here?

a: Anyone new to this area is often amazed by the diversity of plants they find. Thanks to our moderate climate, we can grow more species of plants in the Pacific Northwest than in almost any other region in the world.

Instead of recommending a book, I suggest visiting the Elizabeth C. Miller Library. Housed in the University of Washington's Urban Horticulture Center, it is one of the leading horticultural libraries on the West Coast. It is open to the public, and anyone can borrow books after filling out simple registration forms.

With more than 15,000 books and 500 periodicals, the library's collection covers every aspect of gardening, including an entire section on plant identification and selection. The library's knowledgeable staff can help you find the best resources for your purpose, and you can also bring samples for identification.

If you have a particular plant you would like to identify, you can email a photo or bring a specimen to the library.

You will also need to be familiar with the library's answer line. Staff use library resources to answer questions from professional and home gardeners.

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