A bolt from the blue: You can trust in this salvia to add a shock of colour

As the rest of your garden browns, you can trust in this salvia to add a shock of colour, says Emma Townshend

Your garden has some heart in it at this time of year if there's something still in flower. And you can't get more exhilarating than the medieval deep blue of Salvia guaranitica, or hummingbird sage, which pierces autumnal mornings with its deep azure. While everything else in the garden browns into wintry slumber, the salvia family turns late September and October into carnival season.

Salvias are plants that evolved for life in the subtropics, and, as a result, they require a bit of fuss to nurture them properly. And don't try to fob them off with poor soil or not enough sun. They are aristocrats. But treat them well and you will reap the rewards. In the words of expert enthusiast Betsy Clebsch, "They have the truest blues and brightest reds of any group of plants," and the impact in an autumnal garden is particularly strong.

Just one plant is well worth acquiring, even for a small plot. Dig in some rotted-down manure for best results, mulching with a layer of the same after planting; and a good feed never goes amiss, either. On the other hand, too much feeding and watering and they can overgrow at the expense of flowering: the gardener's dilemma.

Salvia guaranitica is a firm favourite for its long flowering season (if you can get it through the winter, it will start again in June and last until the first frosts): a recommended variety for their deep-blue flowers are "Black and Blue" and "Blue Enigma", but there are paler varieties, such as "Argentine Skies" – elegant stalks with hundreds of blue stars studding them; a real South American treat.

The group has loads to offer besides guaranitica. Salvia fulgens is a red member of the family, a proper fire-engine red, bright enough to stop traffic. It will get up to 5ft tall in a season, but I've heard some gardeners would move it in a pot into a greenhouse for the winter to get it going again the next year. It's an exciting sight to draw your eye to the end of a border where most things are perhaps past their best.

Finally, while its common name of "bog sage" is hardly inviting, Salvia uliginosa pops up in such a lot of gardens lately that it is earning the label "trendy". Kew has huge bushes of it spilling over the paths this September, loaded with sky-blue flowers. Beth Chatto reckoned to get it through the winter in deepest icy Essex with a good layer of mulch, which means it can start next year as early as possible. And then you get to enjoy salvia heaven all over again.

For more salvias and growing information, see 'The New Book of Salvias: Sages for Every Garden' by Betsy Clebsch (Timber Press, £14.99)

Sensational salvias: Beyond guaranitica

William Dyson of Great Comp Garden in Kent (www.greatcompgarden.co.uk) selects three rare treats...

Salvia involucrata is covered in flowers from July to November. They're not fussy, and this one looks good even in bud. A beautiful deep-rose colour. I recommend "Boutin"

Salvia discolor is tender, but just needs putting in a container when the first frosts come; then keep it in a greenhouse over winter. With virtually black flowers over silvery white leaves, it's a show-stopper

Salvia uliginosa is handsome, with lovely flowers. It does best in well-drained soil where the roots are dry during winter

Dyson's specialist salvia nursery is in residence today at the Garden Museum, London SE1 (www.museumgardenhistory.org)