I have several pampas grass plants at a house I recently bought. They are quite tall and bushy. How much (if any) should I prune them back for the upcoming growing season? I need to trim them some for mowing, and have had unprofessional opinions that I can trim them way back.
How you trim your pampas grass (Cortaderia selloana) depends of several circumstances, such as the location of the plants, the condition of the plants and the age of the plants.
But first, if we take a quick peek at some of the anatomy of a grass plant, it is easier for us to understand how the plant functions and grows, and therefore, easier for us to know how to care for it. Grass, like all plants, grow by cell division. In other words, one cell divides to form two new cells. As the two new cells grow to the size of the original cell, the plant elongates ( gets longer). These cells then divide and so on and so forth. This cell division occurs in a specialized region of the plant known as the meristem. Most plants have this meristematic region at the tips of their shoots and the tips of their roots. These are called apical meristems. Trees also have a meristematic region in the cambium (the bark) which enables them to grow wider or gain in girth. So, as the cells divide and expand at the tips of the shoots and roots, the plant gets taller and the roots get longer. If we were to cut the top of the shoot off, a lower branch or stem would become the leader, or dormant lateral buds would break dormancy and continue to grow upwards. This is most apparent when we cut back a shrub to encourage it to bush out.
Grass is different in that it has intercalary meristems which are meristematic regions found at the base of the grass blades. This is the reason lawn grass resumes normal growth after it has been mowed. So, cutting back the pampas grass works on the same principle.
However, this does not mean we should go out and chop it down anytime we get the urge. Grass manufactures two thirds (2/3) of its food through the leaf blade through the process of photosynthesis and 1/3 from the roots. The plant would eventually starve if we were to keep removing the leaf blades. This is also noticeable on many lawn grasses that are mowed too close to the ground.
So, how much to trim? In the more northerly states where winters are harsh and pampas grass less hardy, there may be a lot of damage and die back of the plant. The plant can be rejuvenated by cutting it back to two (2) feet from the ground in the spring before growth starts. In areas where winters are less harsh, it may only be necessary to remove the dead leaves from the plant by cutting them off at the base of the plant. If some of these sharp edged leaves are growing over a sidewalk or interfering with mowing (as in your case), they may be removed at ground level or cut back to within 2 feet from the ground in the spring. It is wise to wear thick leather gloves, a long sleeved shirt, and long pants when working in and around this grass.
Pampas grass will require replanting when the center of the clump starts to die out and growth only resumes at the perimeter of the clump. It can be propagated by division of the younger, healthy parts growing at the edges of the clump. In this case, the leaves can be cut back to several inches from the ground.
