Four o'clock flowers (Mirabilis jalapa) are large, shrub-like plants reaching 36 inches tall and spreading 36 to 60 inches wide. These flowers can overwhelm smaller plants growing in the same area. This long-lived perennial forms masses of gray-green leaves. The showy flowers appear from July through September in pink, mahogany, red, purple or yellow. These trumpet-shaped blossoms open in the late afternoon or evening and close again on sunny mornings. This flower dies back to the ground in the fall and grows again in the late spring.
Loosen the soil with a shovel to a depth of 12 inches in a location with full sun exposure. Work the soil so the texture is the size of small peas. Four o'clock flowers prefer well-draining soil and dry conditions. Mix in a 2-inch layer of compost into the loosened soil.
Dig a hole deep enough to place the top of the tuber 4 inches below the soil surface. Place the tuber in the hole and fill the hole with soil. Pack the soil around the roots.
Water the four o'clock flowers by soaking the soil around the flowers. Keep the soil moist in order to keep the flowers blooming. When exposed to hot, dry conditions, this perennial shuts down by stopping growth and flower production. The four o'clock flower plant revives after the first rain storm once a drought breaks.
Spread a 2- to 4-inch layer of wood chips, shredded bark or straw around the base of the flower plant. This reduces weed growth, which competes for soil nutrients and moisture. It also stops excessive soil evaporation and keeps the soil cool.
Dig the flower tubers up once the leaves have died back after freezing weather occurs in the fall. Shake off the soil and let it dry off. Pack the four o'clock flower tubers in a box filled with dry, peat moss. Store the box in a dry, cool area like a basement or garage that stays above freezing. Replant the tubers in the spring for summer flowers.