PLANT YOUR BORDER

This plant combination demands a sunny site with fertile, well-drained soil – the agapanthus and penstemon in particular dislike winter wet. Before planting, clear away any perennial weeds, then add plenty of well-rotted organic matter to make the soil more fertile and moistureretentive, while also improving drainage. Add grit on very heavy soils. Mulch after planting, taking care not to smother the crowns of plants, and replenish annually.

1 Start with the achillea, helenium and cirsium

These herbaceous perennials share a robust constitution. Plant in spring or autumn, adding extra organic matter to the cirsium and helenium planting holes to give them the moisture-retentive conditions they need to thrive. Take care not to bury the rosette of cirsium leaves and water plants deeply during their first summer. All can be encouraged to produce more blooms by deadheading, but leave late flowers to provide winter structure. Cut back the old shoots to ground level in late February. Plants will bulk up quickly and after two or three years divide them in autumn or spring to spread them further around the garden, or give to friends.

2 Plant the agapanthus and penstemon

Both these semi-tender perennials share a dislike of winter wet, and respond best to planting in late spring to early summer. On the plus side these cultivars (agapanthus ‘Blue Triumphator’ and penstemon ‘Andenken an Friedrich Hahn’) are some of the hardiest available, so if you’ve struggled overwintering other cultivars outside, it’s really worth giving these ones a go. Agapanthus like plenty of moisture when in active growth so pay particular attention to newly established plants in their first summer. If you have heavy soil try growing them in pots in a loam-based potting compost, placing plants into the border when in f lower then overwintering them in the shelter of an unheated greenhouse. Divide container-grown agapanthus every three or four years once actively growing in spring, but don’t bury too deeply or plant in too large a pot. Penstemon is easy to propagate by cuttings. Those taken in late summer can be overwintered in a greenhouse or coldframe as insurance against plant losses. Deadhead flowers before winter, but only cut them back once they’re growing away at the end of April or early May – the top growth offers some winter protection. If you buy new plants in late summer, overwinter in a coldframe or unheated greenhouse and plant out next spring.

3 Finish by sowing the verbena

Although you can pick up young Verbena bonariensis plants, the cheapest way to acquire plenty of seedlings is to sow under cover in March and plant out in early summer. Put some near the front of the border where they’ll provide a fantastic hazy screen to peer through. Established plants usually self-sow around the garden, popping up in gravelly paths and other well-drained places. Plants are fairly short-lived perennials and survival is undoubtedly better on well-drained soil. Shorten some top growth in winter if they’re suffering from wind rock but otherwise leave old stems in place until they’re starting to grow away strongly in spring.