Purpletop vervain

In autumn, cut the shoots back to a hand's breadth above the ground and heap dry leaves or brushwood around the base; a breathable fleece helps in addition in frost without snow cover. A free-draining soil is important, because waterlogging harms more than cold. Leave the seed heads standing, then the vervain reliably self-seeds and comes back in spring even if the root does not survive winter.

Sowing (most common method): Verbena bonariensis germinates in light: do not cover the seeds with soil, or only press them in with a very thin layer (max. 2 to 3 mm), otherwise they will not germinate. Sow under cover from the end of February to early April at 18 to 22 °C; germination is irregular, in about 10 to 28 days. After sowing, water with a fine rose and keep evenly moist until germination. Alternatively, you can scatter the seeds directly in the open ground in autumn; the natural cold period of winter takes care of the stratification and the young plants appear in spring. Purpletop vervain also reliably self-seeds under favourable conditions; for this, loosen the foliage around the base a little in autumn so that the seeds make contact with the soil. The species comes true from seed (not a sterile hybrid), so self-sown seed gives viable offspring.

Cuttings (for deliberate propagation and for frost-prone sites): In spring or early summer, cut strong, non-flowering shoot tips 8 to 15 cm long just above a leaf node. Remove the lower leaves, leaving two to three pairs of leaves at the top. Insert in moist, free-draining cutting substrate (e.g. a mix of compost and sand) and place bright, but not in direct sun. With high humidity (covering with a dome helps) and about 18 to 20 °C, roots form within 2 to 3 weeks. Overwinter rooted cuttings frost-free and plant out after the Ice Saints.

Division (for established clumps): In spring, dig up the rootstock and divide it with a spade into rooted pieces, which you plant at once in the new spot. Divided plants usually flower in the same year. Useful mainly for older clumps that go bare in the middle. Note: in the climate of Central Europe the species is often short-lived and behaves more like a self-seeder than a perennial that can be divided. Sowing and cuttings are usually the more productive routes in a home garden.