How underplanting with salvias can keep roses healthy

A visitor to the garden last summer asked why we grew so few roses. I explained that, out of the many varieties we’d tried, a large proportion had turned out to be too prone to fungal diseases for us to stick with them.

We don’t want to use chemicals at Perch Hill and certainly not fortnightly, the routine usually required to keep roses free of black spot and mildew. Our visitor then confirmed what I had read – that if you underplant roses with salvias, the roses will stay healthy. Alliums have the same reputation.

We’d just finished restoring a barn, and on the south side had created a new garden. We were about to fill the central six beds with herbs and put roses in the larger beds around them. We decided to experiment with the rose and salvia companion planting, so propagated all the salvias we had (see box, right – this is very easy to do and, if you have a propagator with basal heat, there’s still time this year).

In January, the roses went in, mainly strong forms in unusual colours, chosen for good vase life and powerful scent, such as the brown Hot Chocolate, blue-purple Rhapsody in Blue, bright pink Wild Edric and the dark and velvety crimson Munstead Wood and Darcey Bussell. Once the tulips were over in May, all our salvia cuttings were planted in between.

Well, it’s hats off to salvias, as all but Munstead Wood are still pristine now, so late in the year, without a sniff of fungicide. They’re still flowering and have done so (some having a break and then restarting) since the middle of June. That’s in their first year after planting, so it seems that it’s not just alliums that keep roses good and strong; the aromatic salvia family also do a great job.

Pretty partnerships

In terms of overall performance among the salvias, 'Amistad’ – with its ink-black calyx and indigo flower – has stolen the show. It’s been in flower since May and is as covered in bud now in October as it was at the end of spring. It’s a truly marvellous plant that no garden should be without. In fact, it’s such a strong grower, it’s slightly drowned out the much slower China roses, such as 'Mutabilis’ and the species R. glauca with which it is planted. It will go in a different place next year.

The most successful partner we’ve had with 'Amistad’ has been the green-flowered pea species Lathyrus chloranthus, which, unlike its cousins the sweetpeas, is still happily clambering up and through the salvia, covered with new growth and plenty of flowers.

Better with roses are the lower-growing, spreading salvia varieties such as 'Stormy Pink’, the similar-coloured 'Krystle Pink’, along with the luscious crimson 'Nachtvlinder’.

We also love the coral-pink and apricot 'Tutti Frutti’, and similar-coloured but slightly larger-flowered 'Señorita Leah’. With all of these, you can tuck the salvias in under the skirts of the rose. They’ve been a triumph, as well as the larger-growing, but not too drowning, rich, deep pink, S. microphylla 'Cerro Potosí’.

We’ve also had two good reds: 'Wendy’s Wish’ is lovely for the fresh green of its stems, calyces and crenellated foliage, an excellent contrast to the flower colour; and 'Jezebel’, which has slightly smaller flowers; these stand out strongly from the dark crimson calyces and stems.

Potted success

In the same garden, we’ve also had salvias in pots, and they’re all worth repeating. We have the  true-blue species Salvia patens topping an old trough filled with Pelargonium 'Marion Saunders’  and the felted, silvery foliage plant Plectranthus argentatus. The salvia and pelargonium are still covered in flowers.

Among the roses we also have a large pot containing Salvia 'Dyson’s Gem’, with the royal blue Salvia 'Blue Note’ creating a skirt around a purple bell vine (Rhodochiton) climbing over a woven silver birch tepee. This also creates the framework for a pot filled with the huge-leaved Salvia macrophylla. This is on the same scale as 'Amistad’, by now at least five feet tall and also looking good growing with the purple bell vine.

In another pot I love the simple mixture of Salvia 'Cerro Potosí’ planted with Nicotiana 'Lime Green’. In previous years – like our roses – the green-flowered tobacco has been clobbered by mildew, but not this year. It remains utterly pristine.

Our experiment suggests that the line on salvias being the best natural fungicide turns out to be true.