Sage is a useful plant in any herb garden, but the genus, salvia, is valuable beyond the kitchen.

 

 As ever, care is needed when selecting a variety. Many species are tender or half-hardy, like the scarlet pineapple sage, Salvia elegans. They won't tolerate cold, wet winters so they need to be brought into shelter and, being annuals, the first year's flowering is disappointing.

If you choose hardy salvias, though, and provide gritty, slightly calcareous soil in a sunny part of the garden, you'll be rewarded with a fine, colourful summer display. These perennials are best planted in the open ground; even these slow-growers will need repotting every few years.

Salvias are the ideal candidates for a small garden, where every plant must pull its weight and flower over a long period. There's no room for briefly flowering plants, however beautiful. And you get so much more from salvias. Their slightly hairy foliage is often bursting with fragrance that's released on contact - when you rub or brush against it. Even weeding round a bush becomes a joy in such a scented spot.

The dark green leaves of Salvia nemorosa Amethyst are particularly scented. Growing to around 80cm, the shrub has an 80cm spread and produces a mass of spikes, each laden with purple flowers. This sea of vibrant colour lasts for months, with new flower spikes constantly opening. The shrub maintains an attractive bushy shape.

The slightly smaller S nemorosa Caradonna and more compact S x sylvestris Blauhugel have particularly long flowering seasons. Blauhugel's much shorter flower spikes are clear, lavender blue.

Although purples and blues are salvia's usual colours, others are now available. S x sylvestris Schneehugel (Snow Hill) is a vigorous plant, producing an unbeatable splash of white flowers. As with all salvias, you get best results by removing the spent spikes, thereby allowing fresh ones to encourage more flowering. With Schneehugel, you can even use shears for deadheading as this variety flowers in flushes so you can cut off all the spent flowers at once. Other varieties re-flower from side shoots, only needing to have spent spikes snipped off.

The much smaller Salvia nemorosa New Dimension Rose is also unusual. It grows to 30cm, this time producing red flowers. And what could be more suitable for Scotland than the bi-coloured Madeline, with its striking blue and white flowers?

Salvias don't just please the eye, they're also an invaluable source of nectar for bumblebees. A bee-friendly garden needs flowers throughout spring, summer and autumn. You can rely on salvias during the summer to provide worker bees with the nectar they collect from their nests. Later on, males emerge from nests and search out young queens from other nests. After mating, these queens feed on flowers like salvias to build reserves for hibernation.

Plants with flower spikes, like salvias, are perfect for bees. Salvias put a small amount of this precious nectar at the base of all but the top flowers on a spike. The stamens, containing pollen, act like a hinge, swinging as a bee pushes its head into the flower tube, making it brush against the anther and collect pollen. It then collects nectar at the bottom of the tube. The bee is attracted to this nectar bonanza and steadily works its way up the spike. When it enters the upper flowers, it only receives pollen, so the plant can be sure this pollen will be taken to a neighbouring spike where the bee will start again at the bottom. This arrangement suits both plant and insect beautifully.