Take pains to make sure that pets and children have no access to this plant, and even cutting flowers for floral arrangements should be done carefully. Wear gloves and long sleeves when working with monkshood.
Light
Monkshood can handle both full sun and partial shade. Typically, the sunnier the spot, the better for the bloom—however, if you live in an especially warm area, you’re better off opting for a partially-shaded spot so you don’t burn the delicate petals. If you notice the heads or stems of the flower drooping, it is probably receiving too much shade. You may need to stake the plant.
Soil
Monkshood will thrive in any type of moist soil that is well-drained. The ideal soil is a rich, porous loam, but even rocky, mountainous soils can work, provided they receive enough moisture. Dense, poorly drained soils can cause root rot in these plants. Monkshood prefers a soil pH that is slightly acidic to neutral (5.5–7.0), but it can handle extremely acidic soils, as well as slightly alkaline conditions.
Water
A thirsty drinker, monkshood likes to be kept consistently moist but not waterlogged. Frequent watering is important during its growth period (spring) and, once established, monkshood is able to withstand short periods of drought. However, if it’s a robust and lush flowering plant you desire, provide consistently moist soil and make sure it gets a minimum of 1 inch of water each week during the growing season.
Temperature and Humidity
Monkshood is hardy in USDA zones 3 to 8, and it prefers cool summers with relatively low humidity. Keep in mind, that the warmer the weather, the more shade the plant will need.
Fertilizer
Feeding always depends on the quality of your soil. Start with rich soil, high in organic matter, then side-dress with compost and some organic fertilizer each spring. A fertilizer formulated for roses, applied each spring, often works well for monkshood plants that aren’t blooming adequately. Avoid nitrogen-heavy fertilizers. For the amount to use, follow the product label instructions.
Types of Monkshood
In addition to the species form, which is a favorite for its traditional deep blue flowers, there are several good named cultivars to choose from:
‘Albus’ is the familiar monkshood, but with white flowers.‘Blue sceptre’ is a unique bi-colored version of monkshood, featuring white and blue flowers.‘Newry Blue’ has very deep blue flowers.‘Rubellum’ has pink flowers on plants with very finely cut leaves.
There are also related Aconitum species that are sometimes grown as garden plants, though they can be difficult to find:
Aconitum septentrionale ‘Ivorine’ is an early blooming type featuring elongated, white flowers.Aconitum hendyi ‘Spark’s Variety’ is a monkshood with branched flower stalks, giving it a fuller appearance.Aconitum carmichaelii ‘Arendsii’ has azure-blue flowers that appear in mid to late fall on 2- to 5-foot plants.
Pruning
Cutting these plants back after they bloom sometimes produces a second flush of flowers in the fall. Beyond this, no pruning is necessary until you cut the stalks back to ground level after frost kills the plants in the winter.
Propagating Monkshood
Monkshood is usually propagated by root divisions, which should be performed in fall or spring every four of five years as the clumps become dense and congested. Vegetative propagation is also the only way to ensure accurate propagation of named cultivars, as seeds collected from named cultivars often do not “come true” when planted. Make sure to wear gloves when handling the tubers, as the roots contain the greatest concentration of toxins. Here’s how to do it:
How to Grow Monkshood From Seed
Like many perennials, you can start monkshood from seed—however, it can be finicky about germination and may take a year or more to sprout. Because of this, it’s a good idea to start extra seeds, with the expectation that some of them won’t end up germinating. Sow the seed in late fall for germination in the spring—they need to go through a chilling period in winter to break dormancy. The plants don’t really like to be transplanted, so direct sow in the garden if possible. They can be ephemeral during their first year, so don’t panic if the young plants disappear. And it is not uncommon for seedlings to take two years or so before they mature into flowering plants. Make sure that seedlings are kept moist, If you want to sow seeds indoors, they will need a stratification period, chilling the seeds for three weeks before sowing.
Overwintering
Within its established hardiness range, monkshood doesn’t require any special winter protection, but like all perennials, a thick layer of mulch can help moderate freeze-thaw cycles and protect the roots if you live in a region that on the colder end of the hardiness range. Gardeners in zones 3 and 4 may find applying straw or dried leaves helpful for protecting monkshood, though this mulch should be removed promptly in the spring.
Common Pests & Plant Diseases
There are no pests that seriously plague monkshood, but you may encounter some plant diseases. Crown rot, powdery mildew, and verticillium wilt can affect monkshood. Crown rot may occur in dense soils that are poorly draining, or if garden debris traps moisture and fungi around the plant crown. Powdery mildew is usually not serious and can be avoided by ground-level watering rather than overhead spraying. Verticillium wilt is a soil-borne fungal disease that causes stems to turn yellow and wither. Affected plants will need to be removed and destroyed. Avoid high-nitrogen fertilizers, which can make verticillium wilt more likely.
How to Get Monkshood to Bloom
Monkshood is usually a reliable bloomer, producing long-lasting flowers beginning in mid to late summer. Failure to bloom sometimes occurs if the plants aren’t getting the ample moisture they crave. Over-feeding with a nitrogen-heavy fertilizer may also stimulate excessive foliage development at the expense of flowers. Plants begun from seeds may not bloom until their second, or even third year. And it’s common for plants recently divided to experience reduced blooming in the following season.
Common Problems With Monkshood
Monkshood growing in desirable conditions rarely shows cultural problems, but plants sometimes get leggy and tall, requiring staking to keep them from toppling over. After division, monkshood plants may languish for a while before regaining their former vigor. These plants have sensitive, brittle roots, and they often resent transplanting. But this peevishness is usually temporary, and within a year, the divided plants will come back strong.
One common name for this plant—“wolf’s bane”—derives from the plant’s use to kill wolves by baiting meat with plant extract.
