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Salvation for your Roses

With over 300 naturally occurring species, and thousands upon thousands of cultivated varieties to choose from, roses remain hugely popular plants. There cannot be many gardens without at least one. It is hard to kill a rose, but a degree of care is required to get the best from them and create a bountiful display.

One of the most frustrating problems for the rose grower is blackspot. The fungus which causes blackspot, Diplocarpon rosae, is genetically diverse and mutates readily into new strains, just as influenza and coronavirus do in humans. Older rose varieties once proclaimed to be resistant may no longer have the resistance of newer cultivars, though species roses have greater natural resistance. There has long been a misconception that it is difficult to grow roses well in Cornwall because of the damp air and high rainfall, but problems can be minimised with careful selection of a suitable variety and good growing practices. The Nursery has produced a leaflet describing the roses we sell, all of which have been carefully selected as suitable for growing in Cornwall.

The leaves of a rose infected with blackspot develop dark patches or spots, turn yellow and drop off which is unsightly and greatly reduces the vigour of the plant. Young stems may also be affected. Spores are produced in the black lesions on diseased leaves and are spread in water. Leaves left lying on the ground release spores which can reinfect the plant immediately or can lie dormant in the soil over winter to attack the plant the following spring. Wet conditions facilitate a buildup of the problem. All infected leaves should be removed and burned, not composted. Ensuring good airflow around and through the rose, and watering the ground (not the top growth) will help.

There have been various fashions for growing roses over the years. Gone are the days of serried ranks of identical rose bushes, rigidly pruned with bare ground underneath; now they are largely grown in mixed plantings, and as climbers. Nepeta and hardy geraniums are frequently used to underplant roses, their varied colours and form making attractive combinations, but there is another group of plants which is becoming increasingly popular in this situation. Salvias, or sages, have a distinct advantage in that they help control blackspot. They are aromatic plants which release scent as they warm up in the sun. Their scent profile contains sulphur which has fungicidal properties. As the scent wafts up through the rose bush it significantly inhibits fungal growth. Don’t be put off by the idea of sulphurous fumes drifting through your garden, you will not smell eggs.

Salvias are a huge genus of plants, mostly originating from the Americas. Very roughly speaking, salvias for underplanting roses fall into two groups, herbaceous and shrubby. Many are hardy, others half-hardy but with increasingly hot dry climate conditions it is definitely worth trying the half-hardies outside. You could describe them as three quarters-hardy. They all need sun and well-drained soil. Adding grit to the soil at planting will improve their survival. A generous mulch of organic matter over the winter will help, and is doubly beneficial because it smothers blackspot spores which may have fallen onto the soil surface. They are best planted in spring so they can establish well before colder wetter weather arrives.

Recommended herbaceous varieties include S nemorosa ‘Lubecca’ AGM, ‘East Friesland’ AGM and ‘Caradonna’ AGM (which can be seen in the bumblebee garden next to Rose ‘Blue for You’), S x sylvestris ‘Rose Queen’ and ‘Mainacht’. The Wish series are a modern introduction which are good performers. S ‘Amistad’ AGM and the similar pink ‘Amante’ are excellent too. Some of the taller herbaceous varieties will be unsuitable beneath a rose because of their height, but can be planted between and among roses. There are many stunning tall varieties in vivid pinks, blue, and purple, not to mention S confertiflora which is a striking brick red. The hardy perennial varieties can be cut back after the initial flush of flowers, and they will rebloom.

The shrubby varieties are small leaved, twiggy affairs. They include varieties of S x jamensis, S greggii and S microphylla. There is a multitude to choose from. Recommended varieties include Royal Bumble AGM (scarlet), Nachtvlinder AGM (deep violet). Hot Lips AGM (and Amethyst Lips and Cherry Lips) are popular and reliable varieties with an aroma of blackcurrants and bicoloured flowers which are curious in that the proportion of white to colour varies with temperature. As with all salvias, they need well drained soil and sunshine and are best planted in spring. The bare stems can be trimmed a little at the beginning of winter to prevent snagging and wind rock, and cut back to where new growth is visible the following spring.

Salvias come in a huge range of colours so there’s bound to be something to fit your colour scheme. They have a long flowering season, many in bloom from late May into October and November, and they are easy to propagate from cuttings (softwood cuttings in mid summer). Along with nepeta, they are among the very easiest plants to grow from cuttings, so a good subject for beginners. Finally, being rich in nectar and pollen for such a long period, they are invaluable plants for pollinators.