The lupin, known as Lupinus perennis or sundial lupin, is a perennial garden flower native to the UK. It grows in full sun and prefers well-drained, sandy soil. Sky-blue and lavender flowers bloom on stalks up to 90 cm (3 feet) tall during the summer, and they can make attractive floral arrangements. Cutting back flower stalks can help to increase blooming. The plant dies back during the winter but will sprout new growth from its root system the following spring.
Snip off blooming flower stalks at their connection with the base of the plant in the summer, if you want to encourage more blooms.
Cut flower stalks to the base of the plant in the late summer or autumn when they have turned brown and dry, if you want to collect seeds for planting the following spring. Use clippers to cut the stalks at a straight angle.
Cut flower stalks to the base of the plant as soon as blooming is complete if you do not want the plant to release its seeds, which often results in the growth of numerous unwanted plants the following season.
Trim back the entire plant to about 7.5 cm (3 inches) from the ground after its annual blooming season has passed in the late summer or autumn. Wait until the plant has turned yellow or brown and the foliage and flower stalks are dry and crunchy.
This plant attracts butterflies, hummingbirds and other pollinators, which makes it a valuable addition to the landscape. If you forget to prune your lupin in the fall, cut it back in the winter, but do so before the spring when the plant will begin to send up new growth.