How to Plant and Grow Monkshood

Similar to its cousin delphinium, monkshood forms beautiful spires of purple or deep-blue flowers. The blossoms are held above attractive dissected foliage that gives the plant an almost fernlike appearance.

One of the main reasons to grow this stunning plant is for its deep, rich blue flowers. Along with the common blue color, you can find monkshood in pink, white, and sometimes even yellow. The name monkshood comes from the modified petals on the flowers that resemble the cowls or hoods worn by monks. Along with the attractive spikes of the blossoms, monkshood's foliage is quite attractive.

All parts of this plant are extremely toxic to humans and animals. The seeds and roots have the highest concentrations of toxins. If you are growing monkshood, always wear gloves when handling the plants and wash your hands thoroughly when finished. Do not plant it in an area where children play or animals roam.

Where to Plant Monkshood

Choose a location carefully. Once monkshood is planted, it doesn't like to be moved. Select a planting area in partial shade, although the plant will tolerate full sun in cool climates. Monkshood grows best in average, well-drained soil, but it can handle most soil types, from sandy to clay, as long as it is amended to drain well. Its ability to thrive in rocky soil makes it a prime contender for a rock garden.

Although monkshood is often found in rocky settings or garden beds, it is perfectly happy living in a woodland setting as long as the soil is moist and drains well.

How and When to Plant Monkshood

Plant nursery-grown monkshood in early spring. The plant is slow to settle in, but an early spring planting might deliver blooms by fall. Prepare the planting site by digging a hole the same size as the root ball and loosening the soil at the bottom and sides of the hole with a shovel. Put on protective gloves when handling the plant. Slide it out of the container delicately; monkshood doesn't like to be transplanted. Don't loosen the thick roots. Just put the plant in the hole at the same soil level as it was in the container and backfill the hole, pressing down gently to settle the soil. Water the monkshood plant.

Sowing monkshood seed is another option, but success is challenging. The seeds require weeks of cold stratification, so sow them in the autumn in a prepared bed after the first frost. It may take a year for the seeds to germinate, so choose a location that can remain undisturbed for a long time.

Monkshood Care Tips

Light

For the best growth habit, monkshood should be grown in full sun in cool climates. In areas with warm climates, monkshood grows best in partial shade or sunny areas that receive afternoon shade. However, too much shade causes the plants to become floppy and loose in habit, and they'll require support or staking.

Soil and Water

An essential requirement for growing monkshood is consistently moist soil that drains well. The well-draining soil prevents rot in the plant's thick roots. Monkshood also benefits from rich, organic soil that encourages it to put out the lushest growth possible.

Temperature and Humidity

Cool summers and low humidity are a monkshead plant's preferred environment. It blooms best when the temperature remains cooler than 75°, and anything higher may cause the plant not to bloom. Although it tolerates low temperatures, it doesn't handle frost well.

Fertilizer

When monkshood is planted in soil amended with compost or other organic matter, it needs only a single side-dressing each spring of an organic fertilizer or an application of liquid fertilizer designed for roses, following the product directions. Avoid fertilizers that are high in nitrogen.

Pruning

Once the blooms of monkshood are spent, it is best to remove old blossoms to encourage a secondary, late-season bloom. Cutting the plant back by a third after it blooms sometimes has the same result—a bonus late-season bloom. After the plant is killed by frost, cut it back to ground level.

See more of our favorite fall garden plants here.

Pests and Problems

Pests don't bother monkshood much, but diseases can. Overly wet soil can lead to crown rot; do what you can to amend the soil for better drainage. Powdery mildew may show up if the leaves remain wet a lot. It is mostly cosmetic, so try watering from below or removing nearby foliage for better air circulation. Verticilium wilt is much more serious. This fungal disease, which is more likely to occur when the plant is fertilized with a high-nitrogen product, can't be cured. Remove the plant from the garden and destroy it.

How to Propagate Monkshood

Monkshood isn't easy to propagate, but it is possible with divisions or seed.

Division: In early spring, use a shovel to lift the entire plant and its root system out of the soil. Carefully tease the thick roots apart (don't forget your gloves!) until you have two or more divisions. Handle the plant as little as possible; it doesn't like to be moved after it is established. Immediately plant the divisions in well-draining garden soil that has been amended with compost or other organic matter.

Seed: Harvest seeds from mature plants as soon as possible; the older the seed, the less likely it is to germinate. Because they require a period of cold stratification, sow them in the autumn in a prepared bed after the first frost. Clean the planting area and work a couple of inches of compost into the soil to improve drainage. Sow the seeds 6 inches apart and cover them with 1/16 inch of soil. Spray with water lightly to moisten the soil. Monitor the area during the winter and water whenever the top inch of soil is dry.

Find more ideas for cool climate perennials here.

Types of Monkshood

Monkshood

Aconitum napellus blooms in deep purple-blue in late summer. Plants grow to 5 feet tall. Zones 5-8.

'Arendsii' Monkshood

Aconitum carmichaelii 'Arendsii' is a late bloomer with large, intense blue-purple flowers. The sturdy plants typically need no staking unless grown in too much shade. It grows 4 feet tall. Zones 3-7.

'Bicolor' Monkshood

Aconitum cammarum 'Bicolor' features pale lavender to violet flowers with darker purple petals below. It grows 4 feet tall. Zones 3-7.

Monkshood Companion Plants

Astilbe

Astilbe brings a graceful, feathering note to moist, shady landscapes. In cooler climates in the northern third or so of the country, it can tolerate full sun provided it has a constant supply of moisture. In drier sites, however, the leaves will scorch in full sun. Feathery plumes of white, pink, lavender, or red flowers rise above the finely divided foliage from early to late summer, depending on the variety. It will spread slowly over time where well-situated. Most commercially available types are complex hybrids.

Hosta

This plant, hardly grown 40 years ago, is now one of the most commonly grown garden plants. Hosta has earned its spot in the hearts of gardeners—it's among the easiest plants to grow as long as you have some shade and ample rainfall. Hostas vary from tiny plants suitable for troughs or rock gardens to massive 4-foot clumps with heart-shaped leaves almost 2 feet long that can be puckered, wavy-edged, white or green variegated, blue-gray, chartreuse, emerald-edged—the variations are virtually endless. Hostas in new sizes and touting new foliage features seem to appear each year. This tough, shade-loving perennial, also known as plantain lily, blooms with white or purplish-lavender funnel-shaped or flared flowers in summer. Some are intensely fragrant. Hostas are a favorite of slugs and deer.

Toad Lily

No fall garden should be without toad lilies. These Asian curiosities bloom with orchid-like flowers that demand a close look when the garden is winding down in fall. They do best in light shade in humus-rich soil that retains moisture and are suitable for borders or less formal parts of the garden and among shrubs, gradually becoming large clumps. Some self-seed but not aggressively.

Garden Plans for Monkshood

Long-Blooming Rock Garden Plan

This stunning rock garden plan is filled with rugged perennials that provide a pleasing mix of colors and textures. These hard-working plants need a spot in the sun to look their best and provide season-long blooms. Plant around an existing rocky outcrop or bring in a few well-placed boulders or stones for a rock garden that will make the neighbors jealous.

Care-Free Late Summer Garden

This no-fuss garden plan keeps the color coming on strong through the end of the growing season. It's packed with sun-loving, summer-blooming perennials that typically have brighter-hued flowers than those of spring, with warm reds, oranges, and golden yellows taking center stage.