I confess Aconitum is one of my most favorite perennial flowers for full sun perennial gardens and over the years I’ve grown multiple varieties and species of this plant. And no, don’t ask me why as I really don’t know. I will tell you however for the first time in a long time (May/19) I don’t have a single one in my garden.
This is not a plant for a garden with children! Read below for cautions
The Greek (used by Theophrastus) word akoniton used for these poisonous plants is the basis for the Horticultural Latin.
Monkshood comes from the shape of the individual flowers resembling, well… monks hoods. Wolfbane is derived from the use of the roots to poison wolves.
Caution: This plant is extremely poisonous
- The roots and leaves of this plant contain poisonous alkaloids and should be treated with caution.
- The concentration of poison is particularly high in the roots.
- When digging and dividing, take care not to leave the roots lying around.
- There are reports of confusing these roots with horseradish – with disastrous results.
- And different people have varying degrees of sensitivity to even touching the leaves.
In nature, monkshood is found as a woodland edger getting protection from the blazing heat of the sun but allowed to get all morning and late afternoon sun it could gather. As a woodland edger, it would also receive the benefits of leaf litter – a constant and even soil moisture and temperature – to encourage it to bloom.
It is that condition in our gardens that we have to emulate if we want to see this plant truly thrive. If you allow the garden soil to dry out, the performance of this plant will suffer.
Being an edge-of-the-forest plant, you may very well find that monkshood will do well for your clay soil garden. I’d suggest you add as much organic matter / leaf litter in the fall to emulate it’s natural environment but try it if you have clay soils.
If you truly enjoy the blooms of Aconitum, then let me pass along this growing tip. As soon as the blooms are done on the first flowering flush, cut the bloom stalks to the ground and do not allow the plant to set seed. This will encourage it to set another round of flowers later in the summer.
- Bloom time: Early summer to midsummer
- Height: 48” to 60”
- Sun needed: Full sun to light shade
- Bloom color: Blues, violets, white
- Planting space: 12” to 18” apart
- Soil preferred: Humus-rich soil
- Propagation method: Seed, division
- Aconitum carmichaelii the species is also grown and can easily reach 6’ in height. Excellent flowering plant.
- ‘Blue Sceptre’ 48” tall, mid-blue flowers. Good weather tolerance.
- ‘Bressingham Spire’ 48” tall, deep lavender-purple.
- Aconitum hyemale is seldom grown as a species but a variety ‘Ivorine’ is well worth growing.
- Ivorine’ 48” with an off-white – an ivory-white/yellow color – blossom in early summer.
- This propagates by seed and division.
- The seed is notorious for not germinating easily. If you purchase seed, expect it to take at least two winters outside (don’t try germinating it indoors) to start. That way you’ll be pleasantly surprised if it starts earlier. If it doesn’t germinate after two winters, toss it out. It’s dead. See the propagation pages for winter sowing techniques.
- Division is a fall division (or really early spring) and note the roots are quite brittle so do take care when digging and dividing.
The strong blue colors of this plant make it valuable in the summer palette. While some writers have suggested this plant is fine for the part-shade garden, in nature it is a plant of the moist meadow or woodland edge.
The key is to keep the soil constantly moist; as the soil dries out, the performance of the plant deteriorates. This does not mean heavy clay is fine – the constant water will rot the root.
The secret to obtaining good blooms is to have a soil that is high in organic matter and the easiest way to obtain both this and an even moisture supply is to mulch the plant heavily with leaves or other rapidly decaying organic matter. Do cut the plant down immediately after the first flush of blooms is finished; this will encourage the plant to re-bloom.
Aconitum grows best for me in the sunshine rather than the part-shade garden and I would advise gardeners to start it out in their sunniest spot but ensure adequate water is available. I have seen recommendations that this plant grows in the shade but this was not true for me.