Crocosmia, also known as Montbretia, is a vibrant perennial that adds striking color to garden landscapes. Its fiery, trumpet-shaped flowers bloom from mid-summer into autumn, making it a popular choice for gardeners due to its hardiness and ease of establishment.
Understanding Crocosmia
The plant commonly known as Crocosmia primarily refers to the hybrid Crocosmia x crocosmiiflora, a cross between Crocosmia aurea and Crocosmia pottsii, developed in France in 1880. Other common names include coppertips and falling stars. Belonging to the iris family (Iridaceae), Crocosmia grows from bulb-like underground structures called corms.
It has distinctive sword-shaped foliage, similar to gladiolus, from which arching stems emerge. These stems bear trumpet-shaped flowers in shades of red, orange, and yellow. Native to the grasslands of southern and eastern Africa, Crocosmia varieties range in height and flower characteristics, with popular cultivars like ‘Lucifer’ known for their fiery red blooms and robust growth. The flowers attract pollinators such as hummingbirds and butterflies.
Growing Crocosmia
Crocosmia thrives in full sun, though it tolerates partial shade, especially in hotter climates where afternoon shade can be beneficial. More sunlight generally promotes prolific flowering. The soil should be well-draining and rich in organic matter, as Crocosmia does not tolerate waterlogged conditions. Incorporating compost or well-rotted manure before planting improves soil structure and fertility.
Plant Crocosmia corms in spring, after the last frost. Plant corms 3 to 5 inches deep, with the pointed end facing upwards. Space them 3 to 10 inches apart, depending on desired density and cultivar size. After planting, water thoroughly to settle the soil.
Consistent moisture benefits Crocosmia during its active growing season, especially in dry spells. Provide about an inch of water weekly, ensuring the soil remains moist but not saturated. While not a heavy feeder, a light application of balanced, slow-release fertilizer in early spring encourages vigorous growth. Avoid fertilizers with excessive nitrogen, as this promotes leafy growth at the expense of flowers.
For winter care, Crocosmia is hardy in USDA Zones 5 through 9, allowing corms to remain in the ground. In colder regions (Zone 4 and below), lift corms in the fall and store them in a cool, dry, frost-free location until replanting in spring. In milder climates, a thick layer of organic mulch over the planting area provides adequate winter protection. Once foliage naturally dies back in late autumn or early winter, cut it back to the ground.
Managing Crocosmia Growth
Crocosmia has a vigorous growth habit and can spread readily. It primarily propagates through corms, which multiply and form underground chains. Some varieties also spread via stolons (underground runners) and can self-seed, contributing to their expansive nature.
To manage its spread, plant Crocosmia in containers with drainage holes or install root barriers around planting areas. Regularly deadhead spent flowers to prevent self-seeding and encourage more blooms. After foliage dies back in the fall, cutting it to the ground can weaken corms and slow future spread by preventing photosynthesis and energy storage.
Division
Division is another effective method for managing Crocosmia growth and rejuvenating established clumps. Over time, the corms can become congested, leading to reduced flowering. Dividing the plants every two to five years helps to alleviate overcrowding and maintain plant vigor. This process involves lifting the entire clump in either fall or early spring before new growth emerges. The corms, which often form in stacked chains, can be gently separated, and the healthier, topmost corms are then replanted in smaller groups.
Aggressive Spread
If Crocosmia becomes too aggressive in an unwanted area, removing the entire plant, including all corms and stolons, is necessary to prevent regrowth.
Addressing Crocosmia Challenges
Gardeners may encounter issues with Crocosmia, such as a lack of blooms. This stems from factors like insufficient sunlight, as the plant flowers most prolifically in full sun. Overcrowding of corms, often after several years, can also inhibit flowering, indicating a need for division. Inadequate soil moisture or immature corms in newly planted specimens might also contribute to poor blooming. Applying too much nitrogen-rich fertilizer can lead to abundant foliage at the expense of flowers, while pruning foliage too soon after blooming can hinder corm development for the following year.
While generally resilient, Crocosmia can be susceptible to certain pests. Spider mites are a common concern, particularly in hot, dry conditions. Symptoms include fine webbing and discolored foliage. Control measures include regularly hosing down the plant with a strong spray of water to dislodge the mites or applying horticultural oil or neem oil. Thrips can also affect Crocosmia, though less commonly.
Diseases
The plant can also experience specific diseases. Gladiolus rust, a fungal disease, may manifest as blackish-brown or brownish-yellow spores primarily on the leaves, sometimes extending to the flowers. This condition is often associated with low light and high humidity. Preventive measures include ensuring good air circulation and watering at ground level to keep foliage dry. Fungicides containing sulfur powder or copper spray can be applied preventatively in early spring.
Bulb or Rhizome Rot
Another potential issue is bulb or rhizome rot, which occurs in wet, poorly drained soil. Symptoms include stunted growth and yellowing leaves. Affected corms will be soft and emit an unpleasant odor, requiring their removal and disposal.
Environmental Stressors
Environmental stressors also play a role. Extreme heat can cause leaf scorching, while persistently waterlogged soil can lead to root rot.