How to Plant, Grow and Care For Monkshood

Monkshood is a category of tall herbaceous perennials. These bloom in pastel shades of purple, white, and pink. The shape of the flowers resembles little hooded monks, hence the name. The foliage is lacy and delicate, like the stalks of its relative, delphinium.

Aconitum species are tall and sturdy. They look great along fence lines and as a soft backdrop in gardens. In midsummer, it produces flowers on tall stalks.

Monkshood has a rich and dark history rooted in garden myth and folklore. It seems that the fascination with poison and death has intrigued humanity for centuries.

Pythagoras used these plants in 600 BC as a poison to execute criminals. It was also used in Ancient Rome as a potent poison where it came to be known as ‘the queen of poisons.

Fast forward to the Middle Ages when monkshood was used as a poison and was often associated with witches and witchcraft. 

Monkshood also goes by the common name of wolfsbane because it was once used to poison wolves that would kill livestock. Ranchers would create a meat bait laced with the poisonous root, or they would shoot wolves with aconitum-tipped arrows.

In modern times, monkshood is an ornamental garden perennial grown for its beautiful flowers.

Cultivation

Monkshood is part of the Ranunculaceae family. This is also known as the Buttercup family. The large family includes over 2,000 species of flowering plants, including popular garden perennials like delphinium, columbine, and globe flower.

Within the Ranunculaceae family is the Aconitum genus. This genus is conversationally referred to as monkshood or wolfsbane. There are over 250 species of Aconitum. Aconitum napellus is a common garden variety of monkshood.

Toxicity Disclaimer 

All parts of the monkshood plant are toxic. However, the roots and seeds contain the most poison.

The two toxic compounds in monkshood are called aconitine and aconine.  Aconitines affect the nervous system and interfere with the transmission of nerve impulses. If ingested, it can cause nausea, vomiting, irregular heartbeats, difficulty breathing, numbness and tingling, a burning sensation, and muscle weakness. Ingestion could also result in death. There are no antidotes to treat this poison.

Monkshood is highly poisonous if ingested. According to scientists, reports of acute poisoning are extremely rare. Additionally, it is not dangerous to touch the plant, but I do recommend wearing gloves as the sap can be irritating, and you don’t want it to come into contact with any cuts or sores you may have.

Anecdotally, I’ve never had a problem with this plant. I have grown monkshood for years with both pets and young children in my garden. It’s not an appealing plant to most pets, and it is usually in the back of the garden, where it is not easily accessible.

The plant also tastes terrible, so any person or pet who tried it would most likely spit it out immediately. Nonetheless, if you have a curious child or a dog that eats everything, this is not the plant for you.

If you are worried about toxic plants in your garden, remember that many perennials are toxic. Although monkshood is a notoriously poisonous plant, delphinium, lily of the valley, brugmansia, datura, and oleander (to name a few) are also poisonous. 

Propagation 

Monkshood is extremely easy to propagate. It spreads easily by roots and will grow into a large perennial. Let’s examine the four main ways to obtain a monkshood plant for your garden.

Storebought Transplants

Monkshood is easily purchased from garden centers and nurseries during the summer months. Pay attention to the species and variety which will determine the height and color of the blossoms. The benefit of purchasing a monkshood plant is that you can usually find more unique varieties like ‘Bicolor’ and ‘Pink Sensation.’

Choose a plant that looks healthy with glossy leaves. Try to avoid plants with a thick mat of roots coming out of the bottom of the pot. Generally, root-bound plants will experience more transplant shock when planted.

Bare Root

You can purchase bare root monkshood online and in garden catalogs. This is a great way to go if you want a particular or unique variety.

Once you obtain your bare root, soak it in water for at least an hour before planting it. While your plant is soaking, dig a large hole, 2-3 times the size of the bare root.

Next, place the root in the hole with the crown side facing up. Backfill with a blend of compost and native soil. Press it firmly in place.

Water it well and keep the monkshood moist throughout its first season until it gets established.

Growing from Seed

Monkshood is a fairly tricky plant to grow from seed. Seeds require a period of cold to germinate, and they can take a very long time to sprout. Fortunately, a patient grower can still succeed at seed propagation.

Purchase seeds from a reputable seed seller. The simple way to grow monkshood from seed is to sow them directly into the garden in autumn. This allows the seeds to naturally experience the cold exposure they need to germinate and sprout in the spring.

Make sure to water the seeds in well and do not allow the soil to dry out. Use a marker (a stake or stick works great) to mark where you planted the seeds so you will remember where you planted them come spring.

To start monkshood seeds indoors, you must provide cold dormancy in your fridge. An unheated garage may work, depending on the temperature.

Make sure to harden off your seedlings before planting them outside. Plants grown indoors have never experienced weather. Start by bringing your seedlings into a shady area for a few hours, then bring them back in.

Gradually add more time outside and then start introducing sunny conditions to them. This whole process can take about a week.

Keep your seedling watered throughout the process. Move them back to the shade or indoors if you notice them starting to wilt. After they can handle a full day in sunlight, they will be ready to transplant to the garden.

Growing from Divisions

Plant divisions are my favorite way to start monkshood. Divisions grow fast and easily, and finding a neighbor to share it with is not hard. I am always sharing my monkshood with fellow gardeners.

In the early spring or late fall, take a spade and divide a chunk of it off the main plant. Fill the void with compost and soil. Next, place the chunk of plant into a prepared hole (check out the planting guide below for more information on planting). Water it in well.

If you dig up the monkshood and can’t plant it immediately, plant it in a nursery pot and keep it watered and in the shade. Plant it as quickly as possible to reduce shock.

Planting

Planting monkshood is fairly easy and forgiving.

1. Dig a hole at least 2-3 times larger than the plant’s root ball.
2. Remove the plant from its container and gently tease the roots apart.
3. Place in the prepared hole. If the hole is too deep, add some soil.
4. The soil line should be level with the crown.
5. Fill in the rest of the hole with the existing soil and organic matter.
6. Press firmly into the ground.
7. Water well. Your new transplant will need extra water until it is established.

It is best to plant perennial divisions on a cool overcast day to avoid transplant shock. If this isn’t possible, opt for early morning or late evening to avoid the heat of the day.

How to Grow

Monkshood is an easygoing perennial that can spread to cover large areas of your garden. Let’s examine the ideal growing conditions for a happy Aconitum plant.

Sunlight

Monkshood grows in various light conditions, from part shade to full sun. In places with hotter-than-average summers, your monkshood will require more shade than in cooler climates.

In full sun conditions, monkshood will require more frequent watering. As I mentioned above, planting in full sun works best if you live in a cooler climate. If the sun is too strong and hot, it will leave your plant looking crispy and/or droopy.

Part shade to part sun is the sweet spot for monkshood. This is where it will stand up straight with sturdy stalks and won’t require much extra watering.

If planted in an area with too much shade, the plant will become spindly and may need to be staked to prevent it from falling over. Additionally, it may have trouble blooming in the shade.

Keep in mind that gardens evolve over time. A once sunny garden may eventually become shady. If your Aconitum becomes leggy and quits blooming, examine the light conditions. If necessary, you can transplant your monkshood to an area with more sun.

Soil

Monkshood will tolerate a variety of soil conditions. Rich, moist, well-drained soil is ideal for thick, lush plants. But it will also happily grow and thrive in other soil conditions.

These plants will tolerate clay soil, rocky soil, or sandy soil. Just be sure the soil doesn’t get waterlogged. As long as the soil can drain freely, this perennial can grow.

Water

Monkshood requires moderate watering. I only irrigated my monkshood plants in the first season when I planted them and in times of extreme drought.

If you live in a dry climate, you may need to add supplemental watering. They will not tolerate standing water. Make sure the soil can drain excess water. 

Climate and Temperature 

Monkshood grows in USDA hardiness zones 3-8. It prefers growing in cool weather and low humidity. Make sure you are planting in a more shaded area in warmer climates. Shade from the hot afternoon sun is especially important. Eastern exposures are great.

Fertilizer 

I am not a huge advocate for fertilizing perennial beds. Instead, I prefer to focus on overall soil health. Make sure your beds are amended with plenty of organic materials. This can include compost, aged manure, sea soil, or worm castings. I top-dress my perennial beds with a thin layer of organic matter in the fall, once every few years.

You can also apply an organic soil conditioner in the spring. I use one derived from kelp, but worm castings or compost tea work great, too. This keeps all the microbes alive and teeming in my soil. Living soil is healthy soil.

If you want to use fertilizer, sprinkle a slow-release granular fertilizer onto your beds in the spring. 

Maintenance 

Monkshood is a relatively low-maintenance perennial. If growing it in shadier conditions, you might need to stake it, as it will be less sturdy. Monkshood may also need support if you are growing it in an open area with lots of wind. I like growing monkshood against a fence. I will tie it up to the fence if it starts to flop over.

Deadheading the spent blossoms is optional. I only deadhead if I have a small patch of monkshood visible from up close (near a sitting area etc.) But I do not deadhead them if they are in the background of a large garden.

I will cut down the plant foliage as part of my fall cleanup routine. Cut them back to six or so inches from the ground. They will regrow new shoots from the bottom the following year. 

Design 

Monkshood is a beautiful tall perennial that makes a striking backdrop in your garden. 

The cool-colored flowers come in shades of pink, purple, and white. Planting cool-colored flowers in the background of a small garden helps create the illusion of a larger space.

Use monkshood along fences to create a lush backdrop. You can also plant it along a garden’s perimeter to create a natural barrier from deer. They will avoid this poisonous plant at all costs.

Varieties

Aconitum comes in an array of unique varieties and colors.

Aconitum × cammarum ‘Bicolor’

Aconitum × cammarum ‘Bicolor’ is an interesting variety. It features white flowers with purple edges. It has a marbled effect that stands out in the back of a garden. This is my personal favorite variety. It looks striking when planted in the background of gardens.

Aconitum x cammarum ‘Bressingham Spire’

Aconitum x cammarum ‘Bressingham Spire’ is a good classic dark purple variety. It features extra sturdy stems that should not require staking. It is a more stout and short variety, only reaching 3′ in height.

Aconitum anthora ‘Yellow Monkshood’

Aconitum anthora ‘Yellow Monkshood’ is a different species of monkshood than the aforementioned varieties. The flowers are a buttery yellow color.

The flowers are also more elongated on the stem. They look more like Smurf hats than monks’ hoods. It’s a very unique variety that will be noticed in your garden.

Companions 

Gardens always look best with a variety of plants together. Monkshood is a great backdrop plant because it’s tall and flowers in midsummer. These are a few of my favorite plants to plant alongside it.

Hosta 

Hostas look great at the foot of monkshood in a part shade to part sun area of your garden. The low-growing hostas will cover the bottom part of monkshood that can appear tattered and brown.

In midsummer, both your hostas and monkshood will be blooming soft-colored flowers. It’s a lush and striking combination.

Spiderwort

Spiderwort is a partial shade-loving perennial with long grassy foliage and sweet purple flowers blooming in the spring.

The texture of spiderwort is a great contrast against the lacy monkshood foliage. Monkshood will begin to bloom once the spiderwort has finished blooming, making it a perfect pairing. Plant spiderwort at the base of monkshood. 

Coral Bells

Coral Bells are another part shade perennial that looks great with monkshood. The ruffled colorful foliage of the coral bells pairs perfectly with the monkshood’s thick, glossy, lace-like leaves. 

Lily of the Valley

Monkshood and lily of the valley are a toxic twosome that look great together. Be warned, lily of the valley is aggressive and hard to get rid of.

Monkshood also spreads. If you are looking for a couple of shade-loving plants to cover a large area, these two will do it. The lily of the valley will creep along the ground and bloom in the spring. The monkshood will rise above and bloom in midsummer.

Lungwort

I have lungwort planted in my garden at the base of my monkshood. It blooms in the very early spring and then has a beautiful spotted leaf. The monkshood will grow up behind it and then bloom later on. It’s an easy combination.

The fuzzy leaves of lungwort are also unappealing to pets and people. Planting lungwort at the base can help deter pets and children from touching the monkshood.

Pests and Diseases

Because of the poisonous nature of monkshood, it is fairly pest free. It is definitely deer and rabbit resistant. In spite of its toxicity, there are still a few diseases and insects that can attack your monkshood. Let’s examine these common problems and explore some solutions.

Powdery Mildew 

Powdery mildew is an annoying garden fungus. It can affect almost all plants, monkshood included. Powdery mildew can be identified by examining the leaves. They will have a gray filmy powder that can be wiped off. Powdery mildew affects a plant’s ability to photosynthesize and will stunt its growth if it is not treated.

The best way to combat powdery mildew is with prevention. Growing your monkshood in its ideal conditions will ensure healthy plants less susceptible to mildew. This includes part shade to part sun, well-draining soil, and moderate water. 

Plant spacing is also important. Ensure your plants are spaced far enough apart (around 2′) so they have adequate airflow. Another thing to consider is watering. It is best to water your garden straight at the soil line.

A drip hose snaked through the garden works great. Overhead spraying causes wet foliage, which is a breeding ground for mildew. If you have an overhead sprinkler, try to water in the early morning instead of the evening. This way, the sun will have a chance to dry the foliage, and it won’t sit wet through the night.

Of course, if you already have powdery mildew, reading about prevention isn’t helpful. Start by removing heavily mildewed leaves from the plant. Then, spray with a fungicide formulated for powdery mildew. Cut down and remove the old foliage from the monkshood in the fall. In the spring, I would spray the new shoots with the fungicide as a preventive measure.

Crown Rot 

Crown rot is a disease affecting the monkshood crown, where the stems meet the root at the soil line. Crown rot will dissolve the stem near the root, and the monkshood will rot, fall, and die.

If you have stalks of monkshood that are turning yellow and falling over, check the crown of your plant for crown rot. It will be mushy, and there might be some grayish mold forming. You will need to cut down and dispose of all infected plants.

To avoid crown rot, plant your monkshood in loose, well-drained soil. Dense waterlogged clay soil is a breeding ground for the bacteria that causes crown rot.

Delphinium Worm

Delphinium worms can also affect the Aconitum genus. These worms are the larvae of sawflies that will chew holes in your monkshood’s leaves. This will cause your monkshood plant to weaken over time.

If you notice them on your monkshood, remove the leaves and dispose of them. You can treat your monkshood plant with insecticidal soap or neem oil to eliminate the larvae.

Keep your monkshood growing in its ideal conditions to prevent pests such as delphinium worms. Pests are less likely to infest healthy plants. They tend to prey on weakened plants.

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