There comes the sad, woeful feeling of autumn. Missed opportunities, projects unfinished, shortening day length, bad asters. Yep, asters: I can't stand them. The weak lilac blue of these wimpy late-summer daisies may be viewed by more high-minded gardeners as a wonderful sign of the coming season of fruitfulness. But I think the colour is more reminiscent of the touch of fungus on mouldy bread. Especially once the leaves get covered in mildew like swimming kit after a few weeks of school. Really, I should just be glad that asters can't take my opinion of them personally and get involved in some sort of elaborate revenge plan.
There are plenty of horticultural blues, though, that will lift autumnal spirits. Salvias provide a kingly azure in the centre of early October borders, for as long as the frost holds off. These are sturdy plants once they get going, and they relish the alternately sunny and rainy weather we seem to get at this time of year. Salvia patens is a belter, a royal dose of Mexican skies when we most need it. It may only grow knee-high, but watch out for its hallucinatory blue (see box, right, for more details).
For electric impact on a bigger scale, Salvia "Black and Blue" is a plant worthy of its Jagger/Richards title, making an increasing splash every year wherever planted. It'll go way over head height if you let it and the flowers are agapanthus-bright. The only downside is that it lacks Keith's staying power: while they can, last for weeks, if it's a cold winter, you may have to buy it again next year (£9.99 from Crocus).
Ceratostigma (above) is another great autumnal blue: its Latin name "Plumbaginoides" describes the colour of the tropical climber that winds its way around many a Caribbean archway. This plant, though, can stand a fair few cold English early mornings, and will keep flowering through the hour change and beyond. With flowers a deep lapis colour, the plants are compact and do best in a sunny gap or along the edge of a path. They are great front-garden additions, needing little trimming or deadheading and cheering up a journey to the supermarket (£4.99 from Crocus).
Caryopteris is another blue whose October praises I will always sing. "Heavenly Blue" is the zenith of this plant's genius, with little bright powdery flowers that look like smudges of a soft crayon (£9.50 from Burncoose).
Even more excitingly, there are even a few new blues around this autumn to add to the list of well-established royals. Isotoma "Avant Garde Blue" is doing absolutely beautifully in gardens this October, still gaily flowering in huge numbers of tiny lilac-tinged stars. And rare-plant lovers will have clocked the newcomer Lavandula canariensis growing in the front of RHS Wisley's borders this year. It is a lavender native to the Canaries and only occurring there – I'd previously seen it only in a glasshouse at Kew – but Wisley's cunning gardeners have plucked it from botanical obscurity: what greater treat to lift the heart than a brand-new autumnal, zinging blue.
Get the look
Salvia patens ‘guanajuato’: A good variety, currently in stock at Cornwall’s Burncoose at £8.50. After first frosts, cover these salvias with a thick layer of mulch. burncoose.co.uk
Isotoma ‘Avant Garde Blue’: This is pretty enough to have sold out as a plant this year, but seeds (under the name Laurentia) are available in the Kew Collection from Thompson and Morgan at £1.99. thompsonmorgan.com
Lavandula canariensis: Newly brought to gardeners’ attention, and available from spring 2013 from rare-lavender specialists Downderry. downderry-nursery.co.uk