Writing in the Telegraph (not me, not yet!)

Autumn plants: crocosmia, agastache and euphorbia

The partnership of crocosmia, agastache and euphorbia is a smouldering late-season show-stopper, says Val Bourne.

Agastache Blackadder

The blue-black spires of Agastache ‘Blackadder’ lend a dramatic flourish to autumn gardens.

Autumn tends to major in burnished golds, coppery browns and brash yellows, but these can look uninspiring when planted en masse. Adding the sooty, blue-black spires of Agastache ‘Blackadder’ as a contrast adds vibrancy to warm oranges and golden yellows. The late-flowering Crocosmia x crocosmiiflora ‘Star of the East’, for instance, will take on a metallic aura in front of the sultry ‘Blackadder’, producing wide starry flowers that can measure two inches across into late September. The taller acid-yellow heads of Euphorbia sikkimensis, allowed to pop up behind both, will provide added zing through August and September, mingling with the dark agastache.

Crocosmias offer sword-shaped leaves, always a bonus in a border, plus vibrant flowers in sunny colours. The most famous of all is Norfolk plantsman Alan Bloom’s ‘Lucifer’, released in 1966. It became Blooms of Bressingham’s most famous plant, and its clear red July flowers and bright-green pleated foliage were a catalyst that renewed interest in crocosmias.

In the early years of the 20th century, long before Bloom bred ‘Lucifer’, three Norfolk-based breeders (George Davison, George Henley and Jack Fitt) were already raising fine crocosmias. They were probably inspired by Victor Lemoine (1823-1911) of Nancy, France, who raised 55, including ‘Gerbe d’Or’ in 1885. (There is a Plant Heritage National Collection held by Mark and Lauri Fox at The Crocosmia Gardens, Caistor, Lincolnshire – 01472 859269).

‘Star of the East’ (below) was bred by George Davison, the head gardener of Westwick Hall in Norfolk, in 1910. He raised 11 varieties and four are still admired and grown today. They include ‘George Davison’, a July-flowering yellow I grow at Spring Cottage. ‘Lady Hamilton’ is a compact yellow-apricot and ‘Prometheus’, a red-centred deep orange, is said to bear the largest flower of any crocosmia.

However ‘Star of the East’ AGM is widely acknowledged as Davison’s finest because the wide orange-brown flowers, reminiscent of barley sugar in colour, are so substantial and so late to appear. The size of flower is inherited from the pollen parent, a German variety called ‘Germania’. When ‘Star of the East’ was first exhibited in London at Vincent Square in 1912, it was given a first-class certificate from the RHS. After this success Davison concentrated on breeding apples, but donated his crocosmia collection to Sydney Morris of Earlham Hall near Norwich. Morris went on to raise a giant strain known as the Earlham Hybrids, working closely with breeders Fitt and Henley.

‘Star of the East’ has always been hardy for me, so it must have survived in gardens following its introduction in 1910. Graham Stuart Thomas takes credit for rediscovering the large-flowered dazzler at Hidcote Manor Garden in Gloucestershire at a time when crocosmias were thoroughly unfashionable. I am not surprised that ‘Star of the East’ grew at Hidcote. The gardening elite, including Lawrence Johnston, embraced these Norfolk-bred varieties in the Twenties and Thirties. E A Bowles painted many of them and Thomas, garden adviser to the National Trust for 30 years, also spotted ‘Carmen Brilliant’ at Trelissick, ‘Lady Hamilton’ at Powis Castle and ‘Solfaterre’ at Trengwainton and Trelissick.

Agastaches are aromatic plants with candle-like spires of bee-friendly flowers, although some are dubiously hardy. However, ‘Blackadder’, one of the finest new plants to emerge in recent years, has survived for me in my cold Cotswold garden through savage winters, regularly reaching at least a metre (3ft) tall and flowering from July until late September. This recent introduction has caught on quickly and many nurseries sell it, another indicator of hardiness and vigour. The dark core to this blue-black spike is furnished by pale lipped flowers but, as summer turns to autumn, violet-black begins to dominate before the spire fades into winter.

I also grow the equally resilient Agastache ‘Blue Fortune’, a neater violet-blue spike on a shorter plant. This dazzles against Helenium ‘Sahin’s Early Flowerer’, looking almost purple against the orange daisies. Both of these hybrid giant hyssops have loved this damp summer and neither set seed, so flower on for months.

The acid-yellow flowers of Euphorbia sikkimensis (above), a native of the eastern Himalayas, begin to appear in summer. They provide loosely formed round heads of acid-yellow above green linear foliage etched with a pinkish midrib. It runs, as does its close relative the orange-flowered E. griffithii, but not aggressively. It just pops up now and again – a quality I enjoy. Its asparagus-like shoots are a glassy red in spring. The flower heads, held on tall stems, branch and divide so, although this starts to flower in summer, it goes on late if tidied lightly.

How to grow crocosmia x crocosmiiflora ‘Star of the East’ AGM
This is fairly slow growing, unless it’s in a warm position. Being of medium height, it’s best at the front of a sunny border. All crocosmias are rugged and wind-tolerant, but they need moisture-retentive soil to perform and love wet summers. Deadhead after flowering as they can produce inferior seedlings. Divide while the soil is warm, either as the leaves fade in early autumn or in spring as growth breaks. I find the brown-leaved crocosmias and the ones with highly marked flowers (such as ‘Emily McKenzie’) don’t come through the winter in my garden, although they could be grown in containers. I rate the all-red ‘Hellfire’ and the pink-toned orange ‘Limpopo’ very highly.

how to grow agastache ‘Blackadder’

Leave the heads intact for winter interest, and then cut back to the base in early February. Propagate from basal cuttings as the new growth appears. Take three-inch lengths and plunge cuttings into damp horticultural sand. Pot up when rooted. Gentle heat helps. Those on wet, cold clay soil may have problems overwintering agastaches, but this one will come through for most. Best planted in spring or early summer.

How to grow euphorbia sikkimensis AGM
Like all Himalayan plants, this euphorbia appreciates a cool root run in moist soil so it’s not for dry conditions. It rambles less in good, fertile soil, but always provides an airy presence. Snip off the spent flowers if necessary and lift sections in early spring if more are needed. Beware of the sap, which is a skin and eye irritant.

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