Lupine plants (Lupinus spp.) are herbaceous perennials that produce long spike clusters of tiny flowers. The flowers come in a wide range of colors and bloom throughout summer. Lupines grow up to 4 feet tall and 2 feet wide with horizontal leaves and 1- to 4-foot-tall flower spikes that contain small blossoms that resemble those of pea plants. The lupine grows wild throughout most of the colder regions of the United States and prefers to grow in climates where summer nights are cooler. Lupine plants are short-lived and grow best in USDA hardiness zones 4 through 7, where winter temperatures can dip down to minus 25 degrees Fahrenheit.
Select a planting site for lupine that's in full to partial sunlight and has cool, moist soil. If you live in a climate with hotter summers, choose a location that will stay cooler and is in partial shade.
Prepare the planting site by loosening the soil to a depth of 12 to 20 inches to accommodate the lupine plant's long taproots. You can use a rototiller, tilling fork or pitchfork to loosen the soil bed.
Place the lupine seeds in a slightly damp paper towel and store them in a plastic sealed bag in the refrigerator for one week. Alternatively, you can soak the seeds in warm water for 24 hours prior to planting them. Pretreatment will enable the lupine seeds to germinate readily.
Plant the pretreated lupine seeds into the prepared soil bed in spring or early summer. Space the lupine seeds 12 to 14 inches apart and cover them with a 1/8-inch layer of soil.
Water the lupine plants after they sprout once each week during summer in the absence of rainfall or during prolonged dry spells. Ensure that the soil is evenly and thoroughly moistened to a depth of at least 12 inches.
Feed the lupine plants with an all-purpose organic fertilizer for flowering plants once each month while the lupines are actively growing and blooming. Follow the dosage instructions on the label.
Cut the lupine plant's flower stalks back or pinch off the flower heads when they finish blooming and begin to fade. This will encourage a second flowering.