I planted a packet of mixed-color four o’clocks (Mirabilis jalapa) and ended up with one that’s producing beautiful, pure-white flowers. How can I propagate this plant so I can grow it again next year?
Susan Riskind, San Leandro, CA
Four o'clocks are tender perennials. Like dahlias, they form tubers that can be dug and saved.
Photo/Illustration: Jennifer Blume
Becky Heath of Brent and Becky's Bulbs in Gloucester, Virginia, replies: Four o’clocks are indeed lovely, and because their fragrant blooms open in the late afternoon, they are especially beautiful during the evening hours. Your white four o’clock must be exceptionally visible at night, making it a perfect plant for the evening garden. I can understand why you’d like to increase your stock.
Since your white specimen came from a packet of mixed seeds and is probably planted near other brightly colored ones, it’s not likely that seed collected from the white-flowered plant will bloom true. However, four o’clock plants form tubers you can divide to save and propagate desirable forms.
Four o’clocks are hardy in USDA Hardiness Zones 8 to 10. Gardeners in cold climates can dig up tubers after the first hard frost and store them, as they would dahlias, in peat moss or wood shavings in a basement or any other protected location where temperatures stay above freezing.
The next spring, plant tubers outside after all danger of frost has passed, and the soil temperature is about 60˚F or warmer. You can divide the tubers at this point, being sure to leave an eye, or growth bud, on each section.
To give tubers a head start in cold climates, pot them up in containers and place them near a sunny window about six weeks before it’s time to put them outside. This early start will enable you to enjoy their lovely blossoms longer.
In warmer climates where four o’clocks can survive winter, plants will typically go dormant in early fall. This is a good time to lift the tubers and divide them to increase your stock. Whether you’re lifting the tubers to save or divide, be sure to mark the plants while they’re in flowerso you’ll be able to tell the white ones from the others.