Cold comforts

Some climbers are much hardier than others. Fremontodendrons and passionflowers take a great deal less frost than clematis and roses. Fortunately, the listings of the plants awarded the prestigious RHS Award of Garden Merit (AGM) now include a hardiness rating, so it’s easy to see which take the lowest temperatures and which need a choice site or special protection.

The very hardiest plants, which are happy in temperatures as low as anywhere in Europe, are rated H7, while H6 plants are hardy throughout the UK - although if grown in containers in cold areas they may be damaged unless given protection.

See below for a selection of 10 choice AGM-winning, cold-hardy shrubs and climbers. Numbers at the end of each entry refer to the plant's height and hardiness rating.

Snow white

Clematis can vary in their cold hardiness, but the double-flowered clematis Arctic Queen ('Evitwo') is hardy anywhere. The pure white flowers can be up to 18cm (7in) across and open prolifically from May to September. Pruning is simple: cut back by a third in early spring. 2m (6½ft). H6.

Lagoons of blue

Clematis of a very different kind are just as hardy as Arctic Queen. Clematis macropetala 'Lagoon', is a spring flowering form with lovely, nodding, rich lavender blue, multi-petaled flowers up to 8cm (3in) across with creamy centres. The flowers are followed by the welcome bonus of silvery seedheads. Good grown on trellis or through shrubs, this is another great plant for north or east walls. No pruning necessary. 3m (10ft). H6.

Hops with a difference

We all know that hops are indispensible to the brewing of beer, but this golden-leaved form of the humble hop is indispensible in the garden – in the right place. Humulus lupulus 'Aureus' is a vigorous twining climber that needs space to develop, especially as it tends to run at the root, but it’s attractive from when it first emerges to when you cut its vivid foliage and flower clusters for drying. 5m (16ft). H6.

A vivid flowerburst

Many pea species, annual and perennial, are unusually frost hardy. Lathyrus grandiflorus is a case where we must trade off the dramatic display of large, two-tone, violet-pink flowers against the relatively short season. Clinging with tendrils, train it up pea sticks, bean poles or canes towards the back of the border or through a robust spring-flowering shrub such as a forsythia. 2m (6½ft). H7.

Elegant purity

By contrast to the vivid burst of colour from Lathyrus grandiflorus, what is sometimes called the perennial sweet pea, Lathyrus latifolius 'Albus', flowers for months – especially if dead-headed – and the pure white flowers of ‘Albus’ are especially elegant. With up to a dozen (sadly unscented) flowers per stem, I like to mix them with scented sweet peas is small bouquets. 2m (6½ft). H7.

Super-hardy sweet peas

The RHS hardiness rating for annual sweet peas fails to take account of trials conducted at Cornell University in icy New York state when super-scented crimson 'King Edward VII' flowered prolifically after overwintering outside from an autumn sowing in temperatures far lower than we ever experience in Britain. So they’re tougher then we’re led to believe – as long as the drainage is good. 1.8m (6ft). H2.

Tough and fiery

Pyracanthas, with their flat heads of creamy white flowers followed by clusters of red berries, are well known as amongst the best of all evergreen shrubs for the most dependably cold winter situations: north facing walls. The upright growing Saphyr Rouge ('Cadrou'), with carmine-red berries, is an especially good choice as one of the few resistant to scab and fireblight. 3m (10ft). H6.

Rosy glow

In general, roses are very frost hardy and we can depend on most of them - climbers and bush roses, old fashioned and modern - anywhere in the country. 'Chinatown’ is interesting because, basically, it's a tall and upright Floribunda (cluster-flowered rose) which, although it can be grown at the back of a border, is ideal trained as a climber. The pink tints in the fragrant yellow flowers give a pale peachy look 1.8m (6ft). H7.

Summer snow

Clouds of small, white, semi-double flowers cover the 'Sander's White Rambler' rose like an out of season snowfall and with superb fragrance this tough rambler is an very good choice - if you have the space. For this is a vigorous plant, too large for some gardens but magnificent if you have a large mature tree into which it can climb. 6m (20ft). H7.
 

Red perfection

All so-called “japonicas” (Chaenomeles) are very cold tolerant and will flower dependably on north and east facing walls – the coldest situations in the garden. Chaenomeles × superba ‘Nicoline’ gives a delightful splash of deep red-scarlet at a time when few other flowers can provide such vibrant colour 1.2m (4ft). H6.