With their brilliant colors and unusual bottle-brush flower spikes, lupine flowers (Lupinus spp.) can create an early summer focal point in the garden. These highly ornamental plants grow best in U.S. Department of Agriculture plant hardiness zones 4 through 8. As herbaceous perennials that die back and emerge each spring from the roots, lupines reach 3 to 4 feet tall and spread 12 to 18 inches wide. The showy pea-like lupine flowers bloom on tall spikes in blue, pink, purple, red, white and yellow from spring to summer. When grown in the proper culture, lupines attract butterflies to the garden.
Lupine plants adapt to nearly any soil type as long as it drains well. Full-sun exposure produces the best flowers, but these plants tolerate light afternoon shade in climates with hot summers. Mix in 3 to 4 inches of organic material like well-rotted compost into the top 6 inches of soil. This creates a planting site with organically rich soil and improved drainage. Plant the lupine at the same depth that it was growing at in the nursery container.
Watering and Mulching
These flowering perennials perform best when watered each week when the rain does not fall during the growing season. Give the plants at least an inch of water. During hot weather, lupines require more water. It is especially important to water the plants during the first summer after it was planted. This encourages the growth of deep roots. Lupines benefit from organic mulch like shredded leaves or compost. Spread an inch layer of mulch around the plants keeping the mulch off the stems. Mulching keeps the root zone cool during hot weather and prevent water loss through evaporation.
Feeding and Pruning
Lupines do not need a lot of fertilizer, because they are members of the pea family, which can fix nitrogen in the soil. If they are not performing well and are getting adequate sun and water, apply 1 teaspoon per plant of 10-10-10 slow-release fertilizer in the early spring. Water the soil well to start the fertilizer dissolving. Remove the stems and leaves of these plants in the spring before new growth begins by cutting the plant nearly to the ground. After the spikes flower, remove the flower stalks when the blossoms begin to die. This encourages the plants to develop new flowers and stops the formation of seeds. Self-seeding turns into a problem with these plants when "volunteers" pop up in areas of the garden where you don't want them.
Slugs and snails find lupine plants a tasty snack. They eat the blossoms and chew holes in the leaves. Place boards along the edge of the garden and check under the boards each morning for slugs and snails. Remove the pests by hand. Aphids infest these plants heavily at times. Small infestations are controlled by spraying the lupines with a strong stream of water each week for a month. For large uncontrollable infestations, cut the plant back to ground level and destroy the removed stems. The aphids lose their home and the lupine regrows without aphids.
Lupine plants are poisonous when ingested by children and pets. These plants contain toxic alkaloids and enzyme inhibitors, which damage the digestive tract. Even though all of the plant is poisonous, children tend to be attracted to the seed pods that resemble edible bean and pea pods. Lupine poisoning is rarely fatal, but people sensitive to this type of poison can fall into a coma. Some common symptoms of lupine poisoning include depressed heart rate, numbness of limbs, respiratory failure and severe diarrhea. Explain to children that they should not eat theses plants and plant them where they aren't easily accessible by little hands.