Q: I love the annual purple fountain grass, but it's expensive to replace yearly. I tried starting my own from harvested seed, but no go. — Margaret Henson, Gainesville, GA
A: Purple fountain grass (Pennisetum setaceum 'Rubrum') rarely sets viable seed. It's propagated by holding potted plants in a greenhouse or other warm area over winter and making divisions in the spring. The same is true of other colorful forms of this tropical grass. 'Purpureum' is even darker purple, and 'Cupreum' has reddish leaves and copper foxtails. Burgundy red 'Eaton Canyon' is a little shorter than the others, about 30 inches high. Be careful if you grow several of these cultivars together, because with cross-pollination, you might get viable seed. The ordinary color of this pennisetum is green, and many seedlings will not be true to the colors of your original purple fountain grass. More important, for gardeners in the South, the seed grows readily, and Pennisetum setaceum has become a nasty weed in areas that don't get colder than about 20 degrees F, especially in Florida, California, and Hawaii.
If you have a place to protect potted plants from severe cold, you can make your own divisions in the spring. (It would be good to grow at least one potted specimen in a container all season just for this purpose — they make great looking container plants, too.) After fall frost, cut the foliage back to about 3 inches, and move the pot to an unheated garage or any place that does not get much below freezing all winter. Water the pot just enough to keep the soil moist, but not wet. Keeping the plant slightly moist but on the dry side keeps it semidormant. About six weeks before last frost, move the plant into bright light, and resume watering and fertilizing. As soon as you see new growth, you can unpot the plant, divide it into sections that have at least one or two actively growing shoots each, and repot them. The more heat and bright light you give them, the faster they will grow. Remember, this is a tropical plant. Don't put new plants outdoors until tomato-planting time, when all danger of frost has passed.