Commonly known as hemp agrimony, water agrimony, or holy rope, Eupatorium cannabinum is a perennial plant in the daisy (Asteraceae) family. This is a quite large family, consisting of over 32,000 known species. Plants in this family can be found on every continent except for Antarctica. Hemp agrimony in particular is native to Europe, although it can sometimes be found as an ornamental plant in Asia and North America.
Hemp agrimony produces clusters of feathery, dusty-pink flowers. Its common name comes from the fact that its leaves resemble hemp, although these plants are not actually related. Hemp agrimony has a history in European traditional medicine of being used medicinally, although this is not necessarily recommended today. Although it’s a flower and often considered herbaceous, hemp agrimony actually has woody stems.
Facts, Benefits & Uses of Hemp Agrimony
Hemp agrimony flowers are quite attractive to pollinators such as butterflies, dragonflies, and bees. Hemp agrimony’s flowers are dioecious, meaning that male and female flowers occur on separate plants, so this pollination is important for the plant’s reproduction! Interestingly, hemp agrimony’s reddish stems produce a pleasant smell when they are cut.
Additionally, since hemp agrimony is not frost-tender, it’s able to bloom into the autumn, making it particularly valuable to any pollinators that are still out and about during this time when most other flowers have died back. They need this extra energy boost to either help see them through winter hibernation, or migration to warmer locations.
This plant has a long history as a folk remedy and herb, but this is often not recommended because it has properties that can be toxic to humans. This plant has had a wide variety of supposed uses, including everything from fevers and colds to kidney problems.
Hemp Agrimony Growth, Hardiness & Climate
Hemp agrimony is typically happiest in moist, rich soil, and can sometimes be an enthusiastic spreader, able to grow up anywhere from 1.5 to 6 feet tall and spreading via seeds. This plant is generally considered to be easy to grow. An ideal location for this plant is the edge of a pond or stream, which will ensure that it has access to plenty of water. In nature, this hardy flower can be found growing in wetlands, along stream and river edges, and in damp woods, meaning it’s capable of growing in damp soils as well as in an inch or two of standing water. Hemp agrimony’s clusters of pink flowers can be enjoyed by humans and pollinators alike. This plant is hardy in zones 4-8, where it is a perennial.
How to Plant Hemp Agrimony In Ponds
One option for planting hemp agrimony is to grow it from seed. Hemp agrimony seeds should be sown on the surface of soil in the spring in a cold frame, and seedlings can be planted in the summer. Alternatively, seeds can be planted outdoors after the risk of frost has passed. Mature hemp agrimony plants are not frost tender, but seedlings are.
Hemp agrimony can be purchased as a mature plant, in which case gardeners can simply bury the roots so that the beginning of the stem is just above the surface of the soil. Mature hemp agrimony plants can also be divided if desired. Simply gently pull up plants in the spring or autumn, divide them, and replant in soil with adequate water. Mature plants can be planted in damp soils as well as in a few centimeters to a couple of inches of still or slow-moving water. It can tolerate somewhat dry soils, but will not survive extended droughts.
How to Care For Hemp Agrimony
Hemp agrimony is generally considered to be low-maintenance and easy to care for. This plant does best in rich, moist soil with access to full to partial sunlight. However, it can at times be found growing in more dry soils. Gardeners can divide established plants every few years to prevent too much spreading.
How to Winter Hemp Agrimony
Hemp agrimony is native to cold areas and is winter hardy in zones 4 to 8. In these areas, hemp agrimony does not require any special treatment in order to survive the winter. Within hemp agrimony’s native hardiness zones, it is a perennial and can be seen in gardens over many years.
This plant’s foliage will die back in the winter and regrow from the living roots in the spring. Although many people choose to simply cut hemp agrimony down to the ground in autumn, it is actually beneficial to local pollinators such as butterflies to leave the foliage until spring. This is because the caterpillars of some species will survive the winter in fallen leaves and seed heads. Although it may be tempting to clean up your garden, you can help wildlife by holding back.
Is Hemp Agrimony Toxic, Poisonous or Invasive?
Hemp agrimony is native to Europe and portions of northern Africa, but can sometimes be found as an ornamental plant in other areas such as North America and Asia. It is not known to be an extremely aggressive plant, but it can be an enthusiastic spreader and potentially an invasive issue in some areas. For example, there is concern that it can (and has) invade and harm forest habitats. Take care when planting this species in your garden that it does not take over more area than you want it to—you can divide mature plants and either replant or discard the divisions. You can also clean up seeds immediately to deter spread to new areas.
If you live in North America and would like a native plant that looks and functions similarly, we recommend Eutrochium maculatum, also known as spotted Joe-Pye weed, formerly sorted into the genus Eupatorium. Joe-Pye weed is native throughout the majority of the US and Canada, and is easy to grow in damp sites. Please try not to utilize hemp agrimony unless you live in its native range, as it can be quite damaging to local ecosystems and form tall, dense stands that choke out the native vegetation.
Hemp agrimony is known to have some toxic properties, even though it has a history of medicinal use. This plant contains chemicals called hepatotoxic pyrrolizidine alkaloids, which can block blood flow, cause liver damage, and even cancer. For this reason, most doctors do not recommend using hemp agrimony medicinally.
Is Hemp Agrimony Edible? Will Fish Eat it?
The question of whether hemp agrimony is edible is a somewhat complicated one—this plant is considered to be toxic but has been known to be ingested by humans throughout history and to the present day. To be safe, it is probably best to not eat hemp agrimony.
Hemp agrimony is not known to create any dangers for pond fish in particular and is unlikely to actually come into contact with fish since it is not an aquatic plant. Even so, it is always a good idea to clean up plant debris that may fall into your pond.
Where to Buy Hemp Agrimony & Seeds? (UK & US)
Hemp agrimony is available in online and in-person nurseries that sell to the plant’s native ranges. Elsewhere, you will likely have to order it online. Keep in mind that hemp agrimony can become invasive in some environments. As always, do try to select plants for your pond or garden that are native to your area.
