This very extensive article was written by Val Bourne and published in the Daily Telegraph in 2008
This tall, wiry-stemmed daisy shimmers from August until October, producing a haze of lemon yellow just when strident purples, pinks and oranges dominate. Each simple, five-petalled daisy is two-toned, with paler, white-tipped petals set round a darker middle. The ferny foliage creeps up among the cloud of delicate flowers adding even more ethereal charm, and by late summer this Bidens is a border star that bears hundreds of neat flowers reminiscent of a small-flowered cosmos.
Yet few gardeners know or grow Bidens aurea. Indeed, I had to be persuaded to grow it myself because this 3ft-high daisy doesn't look exactly seductive in a small pot on a nursery bench. The stems tend to become ragged and the pot constantly topples over. It also forces itself through the bottom and sides of a small square pot, which rings alarm bells with most gardeners. Yet it isn't a thug: it makes a good-sized clump and likes to travel a little. In the border one is never sure whether newly appearing shoots are seedlings or an escapee runner seeking better ground.
Nomenclature is confused and many nurseries sell this tall, pallid yellow daisy under its previous, long held name B. heterophylla. Until recently, B. aurea was usually applied to a low-growing creeping plant. So ask to see both if you visit a nursery and check the heights.
'Hannay's Lemon Drop', a superior form, was selected by the famous Bath nursery that sadly closed, leaving a legacy of splendid 'Hannay' named plants.
In the wild B. aurea is very variable and 'Hannay's Lemon Drop' may have occurred as a worthy seedling in the nursery, or the seeds may have been collected in the wild and propagated by Hannay's.
One of 200 bidens species, B. aurea is found naturally in the southern states of the USA and Central America. Members of the Asteraceae family, their closest relatives are cosmos and coreopsis.
Bidens' hardiness is often questioned. But mine have come through three extremely wet and bleak winters here, high up in the Midlands. However, cold springs hamper its exuberance. Last year's exceptionally warm April produced precocious July flowers, but this year it is lagging. Typically, B. aurea will flower from August to October continually without deadheading.
This plant will grow on clay and heavier soil as well as lighter soils, but it's more likely to run on lighter ground. It pops up some distance away, weaving itself in among other plants rather than smothering them. And, like many plants that bloom profusely over a long period, B. aurea can flower itself into the ground after two or three years. This is probably why it runs away from the main clump, which can measure a yard in width, in a bid to rejuvenate itself. I know I would hate to be without its cloud of flower on a mellow late-summer or autumn day.
How to grow
Give this plant a sunny position and treat it like a penstemon: don't cut it down at the back end of the year. Leave the top growth as a protective layer until the following spring. If its height offends in winter, reduce the stems by a third. Cut it back hard in April after the worst of the weather is over.
It does not need to be cosseted and can be grown in a windy, airy position; the stiff, wiry stems are self-supporting so there is no staking. The divided foliage allows strong winds to pass through so branches don't snap off.
Always propagate. The easiest way is to collect seeds and these have come true to type for me. Collect them in late autumn (when they are at the thistledown stage) and store for planting the following spring. Germination is straightforward and rapid, around 20 days; each seedling can be potted up, then placed outside by late May.
Alternatively, take cuttings in late spring and early summer by trimming new shoots below a node. Plunge them into gritty compost or damp horticultural sand. Individual cuttings can then be potted up in August. But they are best kept in a pot until the next spring. Over-wintering in a cold frame is ideal, or place in the lea of a north-facing wall as this provides shade, shelter and protection from excessive winter wet. Keep any plants, cuttings or potted cuttings on the dry side all through winter.
B. aurea is also excellent hovering above purple dahlias. These include the purple cactus 'Orfeo', the decorative 'Arabian Night' and the elderberry-purple cactus 'Nuit d'Eté'. It works well close to any tall, dark-leaved dahlia. Or grow it close to the airy Verbena bonariensis - lemon and purple are always sensational together.
Show off the lemon daisies by floating them in front of dark foliage, such as spoon-leaved Cotinus coggygria 'Royal Purple'. The damson purple cotinus highlights the lemon daisies and picks up their form. Or surround it with a tall, dark penstemon such as 'Blackbird', or use the dark beaded awns of a tall, gossamer grass, Molinia caerulea subsp. arundinacea 'Transparent'.
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