Four o'clock, or Mirabilis jalapa, is grown as a tender perennial, but only in USDA Zones 7 through 10. These beauties just can't tolerate so much as a light frost. In cooler regions, Mirabilis is enjoyed as a colorful, easy to grow annual. Often propagated from seed, you'll find that four o'clocks mature much more quickly from bulbs. Plant them this spring, and you'll be cutting blooms from late summer to early fall.
Choose a well-draining area in full sun after all danger of frost has passed. Cultivate the planting site several inches deep. Incorporate 5-10-5 fertilizer into the soil as per packaging instructions. Amend with organic compost, if desired.
Plant four o'clock bulbs at a depth equal to roughly 2 1/2 to 3 times the diameter of the bulb. Space them 24 to 48 inches apart.
Apply a 1- to 2-inch deep layer or organic mulch.
Water your four o'clock plants just enough to keep the site evenly moist throughout the season. They don't like wet feet, but they won't tolerate being allowed to dry out. Keep the planting site free of weeds.
Feed a 5-10-5 fertilizer every 6 weeks all through the growing season once they're about 6 inches tall.
Deadhead plants as blooms fade. Cut stems and foliage back to ground level after they have yellowed completely.