The “keel plant” refers to a group of flowering plants admired for their distinctive floral structures and vibrant displays. They add color and texture to gardens. This guide explores their care for successful cultivation.
Understanding the Keel Plant
The term “keel plant” describes plants with a keel, a floral characteristic. This feature, common in the Fabaceae (legume) family, consists of two fused lower petals forming a boat-shaped structure. This article focuses on the genus Lupinus, commonly known as lupins, which exemplify this form.
Lupins include over 199 species, originating from North and South America, North Africa, and the Mediterranean. These herbaceous perennials grow 1 to 5 feet tall, though some varieties are annuals or small shrubs. Their palmate leaves, divided into multiple leaflets, range from soft green to silvery grey-green. Pea-like flowers are densely arranged on tall spikes, displaying colors including blues, purples, pinks, yellows, and whites.
Cultivating Keel Plant
Light Requirements
Lupins need full sun, at least six hours daily. Partial shade is tolerated, especially in hotter climates, but may reduce flowering. Sunlight encourages blooming and strong stems. In warm regions, afternoon shade protects plants from intense heat.
Soil Preferences
Well-draining soil is essential for lupins to prevent root rot. They prefer a slightly acidic to neutral soil pH. They can grow in sandy, poor soils due to nitrogen-fixing, but amending heavy clay with organic matter and grit improves drainage. Loosen soil 12-20 inches deep for their taproots.
Watering Needs
Newly planted lupins need consistent moisture to establish roots. One inch of water per week, allowing soil to dry slightly between waterings, is usually sufficient. Once established, lupins are more drought-tolerant and only need watering during prolonged dry spells. Overwatering causes excess foliage and root rot. Container lupins need more frequent watering.
Temperature and Humidity
Lupins prefer cooler summers and do not thrive in hot, humid climates. High heat and humidity inhibit flowering. In warmer zones, mulch around the base helps retain moisture and keep roots cool, reducing heat stress. They are hardy and withstand frost to -25°C.
Fertilization
Lupins are legumes; they fix nitrogen from the atmosphere into the soil. Due to this, they generally do not need heavy fertilization. Too much nitrogen promotes leafy growth over blooms. If soil pH is alkaline, an acidifying fertilizer high in phosphorus and potassium can encourage stronger flowering. A slow-release granular formula applied in spring as new shoots emerge is suitable if feeding is desired.
Propagation and Pruning
Propagating lupins can be achieved through seeds, cuttings, or division. Growing from seed is common, but hybrid varieties may not reproduce true to their parent, leading to color variations. To sow seeds, nick the tough seed coat or soak them in warm water for 24-48 hours to improve germination. Seeds can be sown outdoors in early spring or late fall, or started indoors 6-8 weeks before the last frost.
Basal cuttings, taken from new shoots emerging from the base of the plant in mid to late spring, are effective for producing plants identical to the parent. Cuttings should be about 8cm long and inserted into moist, well-draining compost. Division of mature clumps is also an option, though challenging due to the plant’s deep taproot system, with lower success rates. If dividing, select plants with multiple crowns and replant immediately.
Pruning lupins involves deadheading spent flower spikes. This encourages a second flush of blooms by preventing seed production. Cut faded flower stems back to the next set of leaves or a new flowering shoot. In late summer or early autumn, after the growing season, stems can be cut back to just above the plant’s base. Removing dead or damaged foliage in spring promotes new growth and reduces disease risk.
Addressing Common Keel Plant Problems
Lupins can encounter fungal diseases and pests. Fungal problems include powdery mildew, root rot, leaf blight, gray mold, and rust. Powdery mildew appears as a white or grayish film on leaves, especially during cool, dry weather. Root rot results from overly wet soil, leading to yellowing and wilting.
Other concerns include yellowing leaves or stunted growth. Yellowing leaves can signal overwatering, nutrient deficiencies (even for nitrogen-fixing lupins), or slug damage. Stunted growth can also be linked to viral infections like mosaic virus, causing discolored or mottled leaves and twisted stems.
Addressing these problems involves cultural adjustments and prompt action. Proper soil drainage and avoiding overwatering prevent root rot. For fungal diseases, promptly remove affected parts and ensure good air circulation. Controlling sap-sucking pests like aphids, which transmit viruses, is important. Plants infected with mosaic virus do not recover and should be removed to prevent spread. Slugs and snails feed on lupin foliage, especially young plants. Implement control measures to protect plants.