Overview
Astragalus nuttallii (Torr. & Gray) J.T. Howell var. nuttallii is a flowering plant species that belongs to the legume family Fabaceae. This plant is commonly known as Nuttall's milkvetch or Nuttall's astragalus and is native to western North America. It is widely distributed from British Columbia in Canada to California, and from the Pacific coast to the eastern slopes of the Rocky Mountains.
General Appearance
Astragalus nuttallii is a perennial herbaceous plant that can grow up to 50 cm tall. The stems are woody at the base and covered with fine, white hairs. The leaves are pinnately compound with 5 to 9 leaflets, and each leaflet is narrow and elongated, measuring between 1 and 4 cm in length. The flowers are arranged in a raceme, and each flower is about 1 cm long with a purplish or pale pink color. The fruits are long, slender, and densely covered with hairs.
Uses
Astragalus nuttallii has been used for various medicinal purposes by Native American tribes of western North America. The plant's roots were boiled to make a tea that was used to treat a variety of ailments, including cough, cold, fever, and sore throat. In modern times, Astragalus nuttallii is also used as a medicinal plant due to its high levels of polysaccharides and triterpenes, which are believed to have immune-enhancing effects.
The species is also used in ecological restoration projects to stabilize soils, provide food and habitat for pollinators and other wildlife, and to suppress invasive weeds.
Light Requirements
Astragalus nuttallii var. nuttallii typically prefers full sun to partial shade. It requires at least six hours of direct sunlight per day to thrive. Lack of sunlight may result in weak, spindly growth and poor flower production.
Temperature Requirements
Astragalus nuttallii var. nuttallii is native to the western United States, specifically the Great Basin and adjacent mountain ranges, where the climate is semi-arid. It can tolerate a wide range of temperatures, from below freezing in winter to over 100°F (38°C) in summer.
Soil Requirements
Astragalus nuttallii var. nuttallii prefers well-draining, sandy or loamy soil with a neutral to slightly alkaline pH. It can tolerate poor soil conditions, but it is important that the soil is not waterlogged, as this can lead to root rot. In its native range, it is often found growing in rocky or gravelly soils.
Cultivation Methods for Astragalus Nuttallii
Astragalus Nuttallii is a drought-tolerant plant that prefers well-drained soils and bright sunlight. It is best grown in areas with hot and dry summer months and cold winters.
The plant can be propagated through seed or stem cuttings. Seeds should be sown in the fall while stem cuttings should be taken from the youngest growth in the spring, typically in May or June.
When planting, amend the soil with organic matter to improve drainage and fertility. Spread a 2-3 inch layer of organic mulch on top of the soil to keep the roots cool and moist in hot summers.
Watering Needs for Astragalus Nuttallii
Due to the drought-tolerant nature of Astragalus Nuttallii, watering should only be done when the soil is dry to the touch. Over watering can lead to root rot and other fungal diseases. Generally, the plant requires an inch of water per week, but this can vary based on weather conditions and soil type.
Water the plant deeply once a week, making sure the soil is moist to a depth of 6 inches. Drip irrigation systems are ideal for Astragalus Nuttallii since they keep the soil moist while avoiding getting the foliage wet, which can lead to sunburn and other issues.
Fertilization of Astragalus Nuttallii
Astragalus Nuttallii is a light feeder and doesn't require much fertilization. Avoid using nitrogen-rich fertilizers, as these can lead to excessive leaf growth at the expense of flower production. Instead, use a balanced fertilizer, such as a 10-10-10, once a month during the growing season.
A slow-release fertilizer can also be applied in the spring, which will provide nutrients to the plant gradually throughout the season.
Pruning of Astragalus Nuttallii
Pruning is not necessary for Astragalus Nuttallii but can be done to control the size or shape of the plant. Pruning should be done in the fall after flowering has finished.
To keep the plant compact, prune back the stems by half or two-thirds of their length. If a more natural look is desired, simply remove any dead or damaged stems.
Propagation of Astragalus Nuttallii
Astragalus nuttallii (Torr. & Gray) J.T. Howell var. nuttallii, commonly known as Nuttall's milkvetch, can be propagated through various methods, including seed propagation, cuttings, and division. However, the most effective propagation method is through seeds.
Seed Propagation
The recommended time for harvesting seeds of Astragalus nuttallii is during late summer or early fall when the seed pods have turned brown and dry. Collect the seed pods carefully, as the seeds are prone to shattering.
Clean the seeds by removing the pod shells and debris and rinse them with clean water. The seeds can be stratified for around 30 to 60 days before planting to encourage germination. Stratification can be achieved by placing the seeds in a bag with moist sand or by refrigerating the seeds.
The seeds can be planted directly into the ground or raised in containers filled with moist potting soil. Ensure the planting medium is well-draining and water the seeds frequently, keeping the soil evenly moist. Germination of the seeds usually takes about 7-14 days.
Cuttings
Taking cuttings is another method of propagating Astragalus nuttallii. Select a healthy stem and take a cutting in the fall or winter season when the plant has gone dormant. The cutting should be around 4-6 inches long and have at least two nodes.
Remove the bottom leaves and dip the cut end in rooting hormone. Plant the cutting in a well-draining potting medium and place it in a warm, bright location with indirect sunlight. Keep the soil moist and wait for the cutting to root, which usually takes around 4-6 weeks.
Division
Astragalus nuttallii can also be propagated through division. Divide the plant during the fall or winter when it has gone dormant. Carefully dig up the plant and gently separate the roots to create new plants. Replant the new divisions in well-draining soil and water thoroughly.
Disease Management
Astragalus nuttallii (Torr. & Gray) J.T. Howell var. nuttallii is generally a healthy plant, but it can be affected by several diseases. Here are some common diseases and ways to manage them:
- Fusarium wilt: This fungal disease causes the leaves to droop and turn yellow. It is spread through contaminated soil. To manage Fusarium wilt, remove and destroy infected plants and soil, and treat the remaining plants with a fungicide.
- Rhizoctonia root rot: This fungal disease damages the roots, causing stunted growth and yellow leaves. It is spread through contaminated soil. To manage Rhizoctonia root rot, remove and destroy infected plants and soil, and treat the remaining plants with a fungicide.
- Bacterial blight: This bacterial disease causes dark spots on the leaves and stems, which can spread rapidly. It is spread through contaminated soil and water. To manage bacterial blight, remove and destroy infected plants and soil, and treat the remaining plants with a copper-based fungicide.
Pest Management
Astragalus nuttallii (Torr. & Gray) J.T. Howell var. nuttallii is also susceptible to some insect pests. Here are some common pests and ways to manage them:
- Aphids: These small insects suck sap from the leaves, causing yellowing and stunted growth. To manage aphids, release natural predators like ladybugs or lacewings, or spray with a solution of water and insecticidal soap.
- Spider mites: These tiny pests also suck sap from the leaves, causing yellowing and a fine webbing over the plant. To manage spider mites, spray the plant with a strong jet of water, or use a solution of water and neem oil.
- Thrips: These small insects cause leaf distortion and discoloration. To manage thrips, release natural predators like minute pirate bugs or thrips-specific parasitic wasps, or spray with a solution of water and insecticidal soap.
