Ask Mr. Smarty Plants

There are those who say the only good Pampas grass is an eradicated Pampas grass.  That sentiment is understandable since Pampas grass, Cortaderia selloana, is an invasive species in some parts of the country.  It would likely be much more invasive if not for its dioecious nature; that is, it produces male and female flowers on separate plants.  Most often only the female-flowered plants - which are, by far the showier of the two sexes - are sold in nurseries.  Without a source of pollen from a male plant, those big female plumes simply produce no viable seed.  Lest you think you're totally in the clear on creating yet another Hill Country non-native invasion, we would like to remind you that it takes just one male plant (and some people DO grow male plants) to create the right conditions for the next big invasive disaster.  Should you decide to remove your Pampas grass altogether, the Texas native, Muhlenbergia lindheimeri (Lindheimer's muhly), makes a pretty nice, though not quite as showy, substitute.

Now, to answer your question.  In late winter, cut it back hard to within two feet or so of the soil.  Do this before new growth begins to emerge.

Muhlenbergia lindheimeri