How to grow agastache

Despite its name, anise hyssop is only distantly related to hyssop (Hyssopus officinalis) and mint (Mentha spp.). While they're all in the same Lamiaceae family, Hyssop is a small genus of herbaceous or semi-woody plants native to the Mediterranean and central Asia, while Mentha is a genus of fragrant herbs. Lamiaceae is often referred to as the 'mint family'.

In warm climates, annise hyssop comes back each year. However, in colder regions, it's best treated as an annual, where it self-seeds readily. Here in the UK, it may survive winters where there are no frosts. Some cultivars, including ‘Blue Fortune’ are hardy to -15C when established. It's therefore a good idea to try to keep your agastache alive over winter, and use fleece or other methods to protect it.

How to grow agastache

Grow agastache in moist but well-drained soil in full sun.

Where to grow agastache

Grow agastache in a sunny part of the garden. They work well in a mixed border, particularly alongside other drought-tolerant plants, gravel gardens and container displays.

Planting agatache

Prepare the soil as you would for planting any perennial, and add a generous helping of well-rotted manure or compost, to improve nutrient and humus levels in the soil. On heavier soils, add a good layer of horticultural grit to the base of the planting hole, to aid drainage. Then plant agastache at the same depth it was in the pot you bought or grew it in. Firm the soil around the rootball and water well.

Caring for agastache

Agastache is drought-tolerant, so shouldn't need any watering after initial planting. It won't need feeding, either – indeed, too much fertiliser can cause agastache stems to flop and flower production to reduce.

Deadhead spent blooms as and when you need to, and then avoid pruning from autumn as this could promote new growth that may not survive winter.

Protect the plant from frost using fleece or dig up the rootball and move it indoors for winter. In spring, tidy up spent stems and pinch out the growing tips to promote bushy growth.

How to propagate agastache

Agastache can be raised from seed or propagated from existing plants by division.

Where agastache grows as a perennial it can be divided every three to five years. This will not only increase your stock of agastache but rejuvenate your clump. Simply dig up the rootball in autumn and use a sharp spade to slice it into two or more portions. Replant immediately in areas of the garden with similar growing conditions, and water well.

In areas where agastache grows as an annual or where its reliability as a perennial is patchy, then save seed to sow the following spring. Alternatively, as agastache self-seeds readily, transplant seedlings from around the parent plant, in spring. Bear in mind that these seedlings may not be true to the leaf and flower colour form of the parent plant.

Growing agastache: pests and problem-solving

Agastache is relatively pest free.

Agastache varieties to grow

As well as Agastache foeniculum, there are various hybrids and cultivars available, with different degrees of hardiness. These include Mexican agastache (Agastache mexicana), mountain giant hyssop (Agastache pallidiflora) and Agastache aurantiaca. Many flower in different colours and vary in height and spread.

Agastache 'Tango'

Compact agastache with orange blooms from summer into the autumn. Height x spread: 40cm x 50cm.

• Buy Agastache 'Tango' from Worfield Plants

Agastache 'Blue Boa'

Fat spikes of violet-blue flowers appear over a long period. Hardy to -5ºC so will need winter protection. H x S: 60cm x 45cm

• Buy Agastache 'Blue Boa' from Crocus

Agastache pallidiflora 'Rose Mint'

Pink-purple flowers appear over light green leaves, all summer long. H x S: 60cm x 45cm

• Buy Agastache 'Rose Mont' from Mr Fothergills

Agastache 'Purple Haze'

Dense spikes of dark purple flowers. H x S: 90cm x 30cm.

• Buy Agastache 'Purple Haze' from Beth Chatto Gardens