Origin
Erysimum capitatum (Dougl. ex Hook.) Greene var. argillosum (Greene) R.J. Davis, commonly known as Siskiyou wallflower, is a species of perennial in the family Brassicaceae. It is native to the western United States, specifically California, Nevada, and Oregon.
Common Names
Siskiyou wallflower is commonly known by various names, including clay-loving wallflower, argillosum wallflower, and Siskiyou mountains wallflower.
Uses
Erysimum capitatum var. argillosum is a popular garden plant due to its attractive appearance and adaptability. The plant produces bright yellow or orange flowers that bloom from late spring to early summer, making it an excellent addition to any garden. Siskiyou wallflower is also popular in native plant gardening, particularly in areas where naturally occurring vegetation has been disturbed or removed. It is a common sight on rocky slopes, gravelly soils, and cliffs.
Medicinally, the plant is used to treat various ailments, including headaches, rheumatism, and coughs. Native American tribes also used it to induce sweating and reduce fever.
General Appearance
Siskiyou wallflower is a clumping perennial with multiple stems that can grow up to two feet tall and one foot wide. The plant has narrow, lanceolate, blue-green leaves that are up to four inches long. The bright yellow or orange flowers bloom in dense clusters at the top of the stem. Each flower is approximately one inch across and has four petals. After flowering, the plant produces long, upright seed pods that split open when ripe.
Light Requirements
Erysimum capitatum var. argillosum typically prefers full sun to partial shade. It can tolerate some shade, but the plant may not flower as abundantly in shady conditions. In areas with very hot summer temperatures, some shade during the hottest part of the day may be necessary to prevent scorching.
Temperature Requirements
This plant is native to dry, rocky areas of western North America and is adapted to a wide range of temperatures. Erysimum capitatum var. argillosum can tolerate temperatures as low as -10°F (-23°C) and as high as 110°F (43°C). However, it grows best in areas with moderate temperatures, between 60-75°F (15-24°C).
Soil Requirements
Erysimum capitatum var. argillosum prefers well-drained, sandy or gravelly soils that are low in nutrients. It is commonly found growing in rocky or sandy areas with low organic matter. However, the plant can tolerate a range of soil types, including clay and loam, as long as the soil is well-drained. The pH range should be slightly acidic to neutral at 6.0-7.5.
Cultivation Methods
Erysimum capitatum var. argillosum grows best in well-draining soil that is rich in organic matter. The plant thrives in sunny areas with good air circulation. Erysimum capitatum var. argillosum cultivars are tolerant of some shade, but they perform better in full sun. Do not plant the Erysimum capitatum var. argillosum in areas with poor drainage to avoid root rot.
Watering Needs
Erysimum capitatum var. argillosum requires regular watering, especially during the growing season. The plant needs deep watering, but the watering must be infrequent to avoid waterlogging the soil. The watering frequency also depends on the type of soil and weather. During the dry spells, water the Erysimum capitatum var. argillosum more frequently.
Fertilization
Erysimum capitatum var. argillosum requires regular fertilization to encourage growth, blooming, and maintain vibrant foliage. Apply a balanced, water-soluble fertilizer during spring and summer. Avoid applying fertilizer in late fall or winter to avoid promoting foliage growth, which can be damaged by the cold.
Pruning
Erysimum capitatum var. argillosum cultivars require pruning to maintain shape and reduce the risk of fungal diseases. Prune the plant in late winter or early spring when the growth period begins. Cut back dead and damaged growth to the base of the plant. Regularly pruning the Erysimum capitatum var. argillosum will encourage bushy growth and promote healthy blooming.
Propagation of Erysimum Capitatum var. Argillosum
Erysimum capitatum var. argillosum can be propagated through different methods. The following are some ways to propagate this plant:
Seed Propagation
Seed propagation is the easiest and most effective way to propagate Erysimum capitatum var. argillosum. The seeds should be directly sown into the soil in the fall or early spring when the soil is moist. The seeds should be sown in a well-draining soil mix and covered with a thin layer of soil. They should be kept moist until the seedlings emerge. Once the seedlings have established their roots, they should be transplanted into their permanent location.
Cuttings Propagation
Erysimum capitatum var. argillosum can also be propagated through stem cuttings. The cuttings should be taken in the early summer when the plant is actively growing. The cuttings should be at least 4 inches long and taken from new shoots. The lower leaves should be removed from the cutting and a hormone rooting powder should be applied to the cut end. The cutting should be planted in well-draining soil and kept moist until roots develop.
Division Propagation
Erysimum capitatum var. argillosum can also be propagated through division. This should be done in the early spring when the plants are emerging from dormancy. The plant should be dug up and divided into smaller sections using a sharp knife or garden spade. Each section should have healthy roots and stems. The plants should be replanted in a well-draining soil mix and watered until they become established.
Disease Management
Erysimum capitatum var. argillosum is generally a healthy plant that can withstand some disease pressure. However, there are certain fungal and bacterial diseases that can cause severe damage to the plant.
One of the most common diseases affecting Erysimum capitatum is powdery mildew. It is characterized by a white, powdery growth on the leaves, stems, and flowers of the plant. To manage powdery mildew, it is recommended to keep the plant dry by avoiding overhead watering and increasing air circulation. Additionally, the infected plant parts should be removed and destroyed to prevent the disease from spreading.
Another disease that can affect Erysimum capitatum is downy mildew. This disease is characterized by a grayish-white growth on the undersides of leaves, which can turn yellow and fall off prematurely. To manage downy mildew, it is recommended to improve air circulation, avoid overhead watering, and remove infected plant parts.
Verticillium wilt is another disease that can affect the plant. It is a soil-borne disease that causes the leaves to yellow and wilt, eventually leading to the death of the plant. There is no cure for verticillium wilt, so it is important to prevent it by planting in well-draining soil and sterilizing garden tools between uses.
Pest Management
Like all plants, Erysimum capitatum is vulnerable to pest infestations. Here are some common pests that may affect the plant and how to manage them:
Aphids are small, soft-bodied insects that can pierce the plant's tissues and suck out sap, causing distorted growth and yellowing of leaves. To manage aphids, it is recommended to spray the plant with a strong, targeted stream of water or apply insecticidal soap or neem oil.
Spider mites are also common pests that can damage Erysimum capitatum. They are very small and can usually be found on the undersides of leaves, where they suck out the plant's fluids, causing yellowing and stippling. To manage spider mites, it is recommended to spray the plant with a strong stream of water or apply insecticidal soap or neem oil.
Finally, snails and slugs can also be a problem for Erysimum capitatum. They can chew on leaves, stems, and flowers, leaving large holes and damaging the plant's overall appearance. To manage snails and slugs, it is recommended to handpick them off the plant or set up traps with beer or a commercial bait.
