Eupatorium: location, pruning & use as a medicinal plant

Eupatorium has been used as a medicinal plant for thousands of years. Other than that, the different plant species and varieties are a real asset to the garden.

If you decide to plant the so-called hemp agrimony in your garden, you can count on lively visits from butterflies when the boneset (Eupatorium) is in bloom. In this article you will learn more about the optimal location for boneset, possible care measures and the medicinal uses of Eupatorium.

Eupatorium: origin and properties

As well as the synonym hemp agrimony, the plant is also called boneset. The Eupatorium genus is classified in the daisy family (Asteraceae) and includes about 40 species and several hybrids. Hemp agrimony (Eupatorium cannabinum) is the only species native to Europe, North Africa and the Middle East. The rest are mostly found in North America, with some variants in East Asia. Natural habitats for many species include wet embankments, floodplain forest clearings and fresh to moist woodland borders.

The external characteristics and properties of the species and varieties of boneset all differ somewhat and cannot be generalised in principle. The genus includes annual and perennial herbaceous species, the latter being the main component. The growth habit is upright, bushy to slightly overhanging. The height of growth varies greatly from species to species and usually ranges from 40 to 200 cm. The deciduous boneset is very frost-resistant.

The erect stems of the cunegonde herb are usually not branched until flowering. The stalked or sessile leaves of boneset are somewhat reminiscent of the leaf shape of a hemp plant (Cannabis) – hence the name hemp agrimony. With smooth or serrated margins, the lanceolate, pinnate leaves stand together on the stem in numbers of 3 to 5.

The hermaphrodite tubular flowers are arranged in umbrella-shaped or panicled flowerheads. Whether pink, purple, lilac or white – the flower colours also vary depending on the species and variety. Eupatorium is a very important food source, particularly for butterflies: it provides lots of nectar as well as pollen. Brownish to black, narrow, closed fruits called achenes form on the withered flowers, with a hairy calyx – similar to the dandelion (Taraxacum).

When does eupatorium flower? The flowering period of eupatorium usually ranges from July to September or from August to October.

Tip: typical pollinators of eupatorium include the small fox (Aglais urticae), the admiral (Vanessa atalanta), the Russian bear (Euplagia quadripunctaria), the emperor’s coat (Argynnis paphia), the ducat butterfly (Lycaena virgaureae), and the holly blue (Celastrina argiolus). You can learn more about perennial visitors in our article on the most popular native butterfly species.

Planting eupatorium: location and method

The optimal site conditions may differ somewhat depending on the species, as already mentioned. Generally speaking, eupatoriums prefer a moist location with permeable and nitrogen-rich soil. The composite plant enjoys light, partial shade but with sufficient water supply, the boneset can also tolerate a sunny location. Suitable habitats include moist open areas, moist to wet edges of water bodies, or fresh to moist woodland borders.

Spring is the best time to plant eupatorium. When digging the planting hole, the soil can be improved – if necessary – by applying fertiliser. Very light, sandy soils can be enriched with high-quality compost. Our peat-free Plantura Organic Enriched Compost is ideal for this purpose – its high humus content not only improves the fertility of the soil but also its ability to store water, which is important for the boneset.

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The initial nutrient supply is already provided by mixing in the substrate. Very heavy, compacted soils should be mixed with sand to prevent waterlogging. As for planting depth, the surviving buds should be planted just below the soil surface. The plant can now be planted as deep as before and watered well. Because of its sprawling growth habit, boneset is best planted alone or in small groups of 2 to 3 plants. Therefore, a planting distance of around 100 cm should be maintained.

Combining eupatorium: an attractive combination can be created in the garden by using cuckoo carnation (Silene flos-cuculi) in an area around the boneset.

The right care

After planting, boneset requires more or less intensive care depending on the variety. We explain below which measures are carried out under which circumstances.

Watering and fertilising

A constant water supply is especially important in sunny locations and during hot summers. In these cases, boneset requires additional watering. The soil should always be well moistened. Those who cannot meet this location requirement in their own garden should plant the boneset in a large planter and water regularly. Since the cunegonde herb is a real nutrient-zapper and thus prefers nitrogen-rich soils, attention should likewise be paid to a sufficient nutrient supply. Compost application when planting in spring gets the boneset off to a good start: in summer, renewed fertilisation with compost or slow-release fertiliser granules can take place. It is important to note here that the fertiliser should not be applied too late, otherwise this may adversely affect the frost-resistance of the plants.

Tip: boneset is not salt-tolerant and thus should not be fertilised with mineral fertiliser.

Pruning eupatorium

You should remove wilted flowerheads near the ground before the onset of new growth. This can be done either in October or in early spring. Due to the decorative effect of the woolly-looking flowerheads, the later time for pruning is more recommended. Optional pruning to about 40 cm can be done in mid-May. As a result, the eupatorium will grow a little stouter and forms more flowerheads. In this form, the flowers are also more suitable for use as cut flowers.

Dividing eupatorium

Particularly in nutrient-poor locations, it makes sense to rejuvenate the boneset every 2 to 4 years by dividing it. This is not mandatory in optimal locations as the plant has a naturally long lifespan. However, dividing can used to reduce strongly proliferating specimens of the eupatorium. In doing so, you also multiply your plants at the same time.

Tip: since some species or varieties of eupatorium can reach rather majestic heights, it is helpful to give the plants some stability if they are located in a place exposed to wind. For this, tie the eupatorium with a jute rope and attach it to a pole or stake.

Is eupatorium hardy?

The majority of perennial species and varieties of eupatorium are hardy down to around -34 °C and thus do not require any additional protection. In some cases, the frost-resistance is about -28 °C, which is still perfectly adequate.

Propagation

The easiest way to successfully propagate boneset is by division. To do this, dig up the entire plant in the spring and cut the root ball with a spade. The plant parts can then be re-buried and watered. The plants automatically rejuvenate through this method of propagation and grow better afterwards than before, which is an advantage of this method.
If you allow the boneset to grow freely and do not remove the withered flowerheads in good time, you can expect this riparian plant to self-seed. However, this does not cause the boneset to spread too obtrusively – so there is no need to worry. If you want to prevent seeding, you can intervene by removing the seed stems. New seedlings can also grow on their own from the seeds. Below we have summarised how to seed boneset:

• Best time: spring
• Fill sowing tray with permeable substrate
• Place seeds on substrate and cover lightly with soil
• Keep soil moist
• Germination temperature: approx. 18 – 20 °C
• Germination period: approx. 2 – 4 weeks

Tip: if after 6 weeks there are still no seedlings to be seen, it is best to proceed as for sowing cold seedlings – the seeds may be too old and have fallen into a deeper dormancy.

Harvesting and use of boneset

In folk medicine, this cunegonde herb was increasingly used for fever, colds, constipation, loss of appetite and more. However, new findings suggest that utmost caution should be exercised when consuming the herb. Consumption of independently harvested plant parts is not advised. The boneset can also be used for external application in the form of compresses, ointments or tinctures. In one study, it was found that boneset has a high medicinal potential but this still needs to be explored in depth.

Is boneset poisonous?

Despite its various medicinal effects, boneset should never be consumed in excessively high amounts. It is best to use only preparations available in pharmacies in the recommended dose. This is because boneset contains toxic substances such as the flavone eupatorin. If the dosage is too high, vomiting and diarrhoea may occur. In general, pregnant women and children should not consume it. Long-term use may also cause liver damage. The same applies to animals when larger amounts are ingested.

Another attractive and exceedingly insect-friendly perennial is purple loosestrife (Lythrum salicaria). With its good supply of nectar and pollen, it is a particularly important food source for wild bees and butterflies. Just like boneset, this plant prefers a sunny to semi-shaded location at the water’s edge or in an open area with moist soil.