Introduction
Lupinus subalpinus Piper & B.L. Robins., commonly known as the subalpine lupine, is a perennial plant of the Fabaceae family. Native to the western United States, it is found in high-elevation meadows, subalpine forests, and alpine slopes.
Appearance
The subalpine lupine can grow up to 1 meter tall and has a bushy, upright growth habit. Its leaves are palmately compound with 7 to 10 leaflets, and its blue-purple flowers grow in a tall, dense raceme. The plant produces long, narrow seedpods filled with small black seeds.
Common Names
The subalpine lupine is also commonly known as the mountain lupine, alpine lupine, and Robins' lupine.
Uses
The subalpine lupine has little known medicinal value, but it has important ecological roles. It is an important food source for many species of wildlife, including elk, deer, and small mammals. The plant also helps fix nitrogen in the soil and can be used in ecological restoration projects to improve soil fertility. Additionally, the subalpine lupine is often grown as an ornamental plant in gardens and landscaping due to its tall, striking flowers.
Light Requirements
Lupinus subalpinus Piper & B.L. Robins typically requires full sun to prosper. The plant will not grow densely or bloom well in shaded spots. It tends to grow in rocky areas or exposed slopes with full sunlight. Inadequate sunlight can make the plant spindly and weak, reducing its overall vigor.
Temperature Requirements
Lupinus subalpinus prefers cold, moist temperatures. In its natural habitat, it is typically found in the subalpine zone between 1,800-3,200 meters elevation, where it can experience winter snowpacks. It is relatively cold-tolerant, with winter low temperatures usually ranging from -7°C to -20°C. During the growing season, temperatures range between 10°C to 25°C, with diurnal fluctuations of up to 10°C. The plant cannot withstand prolonged heatwaves or droughts.
Soil Requirements
The plant grows well in well-drained or slightly dry soils, usually in sandy or rocky substrates with a pH range around 6.0 to 7.5. The soil should have a good amount of inorganic matter with enhanced drainage and aeration capacity. The plant can handle nutrient-poor soils, but it does prefer soils with a diverse microbial population. Lupinus subalpinus also cannot withstand waterlogged soils, which typically stunt growth and cause root rot.
Cultivation methods for Lupinus subalpinus Piper & B.L. Robins.
Lupinus subalpinus Piper & B.L. Robins. is a herbaceous perennial plant that prefers well-draining soil with a slightly acidic pH. It can be grown in full sun to partial shade. The plant is hardy and resistant to drought. It is best to sow the seeds directly into the soil and avoid transplanting. The seeds should be planted at a depth of about ¼ to ½ inch (6 to 13 mm) and about 6 inches (15 cm) apart.
Watering needs for Lupinus subalpinus Piper & B.L. Robins.
Although Lupinus subalpinus Piper & B.L. Robins. is drought-resistant, it still enjoys consistent moisture. Watering should be done when the topsoil is dry. However, care should be taken not to overwater the plant as it can lead to root rot. The best time to water is in the morning, which gives enough time for the leaves to dry during the day and avoid fungal diseases.
Fertilization of Lupinus subalpinus Piper & B.L. Robins.
Lupinus subalpinus Piper & B.L. Robins. is a nitrogen-fixing plant and does not require extra fertilization. However, if the growth is subpar, a well-balanced fertilizer can be added in early spring, before the plant enters the blooming phase. It is best to avoid fertilizers that are high in nitrogen, as it can lead to leafy growth at the expense of flowers.
Pruning of Lupinus subalpinus Piper & B.L. Robins.
Lupinus subalpinus Piper & B.L. Robins. does not require pruning. However, spent flower spikes should be removed to encourage new growth and prolong the blooming period. Once the plant has finished flowering, the entire stem can be removed at the base. This can also help prevent self-seeding, which can become invasive.
Propagation of Lupinus subalpinus Piper & B.L. Robins.
Lupinus subalpinus Piper & B.L. Robins. is commonly propagated by seed. Collect mature seed pods in the fall before they burst open and scatter the seeds. Air-dry the seed pods in a warm, dry location, and then separate the seeds from the pods. Store seeds in a cool, dry place for planting in the spring.
Scarification, or nicking or filing the seed coat, may help improve the germination rate. Soaking seeds overnight in water before planting may also speed up the germination process.
Seeds should be planted in well-draining soil in a sunny location. Plant in the spring when the soil has warmed up, or in the fall before the first frost. Cover the seeds with a light layer of soil, and keep the soil moist until germination occurs in 2-3 weeks.
Alternatively, Lupinus subalpinus Piper & B.L. Robins. can also be propagated through division in the spring or fall. Gently dig up the plant, being careful not to damage the roots, and carefully separate it into smaller sections. Replant each section in soil with proper drainage and sunlight.
Disease Management
The Lupinus subalpinus Piper & B.L. Robins. plant can be affected by various diseases, including:
- Anthracnose: This disease causes brown or black colored spots on the leaves. The spots later enlarge, often causing the leaves to curl and die. To manage the disease, remove and destroy the infected leaves well before flowering. Use copper-based fungicides to prevent future outbreaks.
- Root Rot: This disease is caused by fungi that damage the roots, causing them to rot. The plant may eventually wilt and die. To prevent root rot, avoid overwatering the plant. Improve soil drainage, and apply soil fungicides to the plant's base.
Pest Management
The Lupinus subalpinus Piper & B.L. Robins. plant can be attacked by both insect and animal pests such as:
- Thrips: These tiny insects feed on the plant's leaves and stems causing deformities and discoloration. They also contribute to the spread of viruses. To manage thrips, use insecticidal soap as soon as you notice any signs of the insect. Repeat the application after a week or two.
- Deer: Deer can cause significant damage to the plant, feeding on the leaves and flowers, damaging the stems, and even uprooting the plant. To protect the plant from deer, install deer-proof fencing around the plant's perimeter or use deer repellents that contain natural ingredients from predator urine.
