Salvia involucrata, a big showy subtropical sage

For sheer size and winter colour, Salvia involucrata varieties are outstanding in our subtropical garden.

This is the original salvia in our collection. When we first moved into Hill House there was a well established patch growing at one of the entrance gates. It’s well away from the current house but nicely placed on the driveway to announce the house paddock with big pink flowers from autumn to spring.

Naming

Salvia involucrata is one of the variable Salvia species, which has probably been crossed with other species to give its range of cultivars. My initial searches to find a plant that resembled it led me to think it was Salvia wagneriana, going from labelled photos. However Sue Templeton at Unlimited Perennials suggested that it might actually be Salvia involucrata. Now that I have both species from her collection I can see that wagneriana has a different leaf, and my original plant is like her involucrata. The closest photo I have seen to my plant (at Rolando Uria’s site) was named an involucrata/wagneriana cross.

There are at least three similar salvias which would seem to be likely contenders for crossing, with similar inflorescence types; involucrata, wagneriana, and karwinskii. Salvia wagneriana has a congested inflorescence that is somewhat rose-like at early flowering. Salvia karwinskii has a loose, elongated inflorescence, with the flowers well spaced along the spike, and Salvia involucrata seems to be intermediate, although still well-spaced once the first few flowers have finished.

Two further complications are that cultivars listed as involucrata flower in the long days, rather than the strictly short-day flowering of my form. Robin Middleton lists ‘Bethelii’, ‘Joan’ and ‘Hadspen’ as all starting in the English Summer. He also thinks that ‘Joan’ little resembles an involucrata, and seems to have strong microphylla parentage.

Cultivation

salvia wagneriana pruned
The Salvia involucrata clump cut down to ground level.

This is a big salvia. It grows as canes which can be longer than 4 metres and arch with age to touch back to the ground. The canes grow from crowns, and the clump spreads moderately by suckering, seeds, or layering. Our clump covers a big area, maybe 5 x 10 metres, and sits in the afternoon shade of trees and some tree-sized bamboo.

The original clump was part of an overgrown garden, neglected for years and partly invaded by lantana, so my first job was to get in, cut it back to the ground, and clear it out.

I guessed that winter, after the main flowering, would be a good time to cut it back. Fortunately the climate here is right for that sort of treatment, but I gather that a winter prune in colder climates could easily kill the plant (although it might not overwinter in cold climates at all). As you can see from the picture, I took it down to gr

salvia wagneriana
Salvia involucrata flowering in autumn

ound level and waited for it to re-shoot.

It responded vigorously, and by April was back to flowering, on the new canes. Another reason to cut back in Winter here is that we usually get a dry spell sometime between August and October. The new shoots start in August, so cutting back the old canes possibly reserves moisture for them to make a strong start.

Salvia involucrata is such a robust plant here that it really belongs at the back of a garden, or even as a broad hedge. It forms a bank several metres high, and is
essentially impenetrable, but does look good year round.

Propagation

dam wall 170517
The dam bank in May, covering well and starting to flower
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The dam bank in March, after planting out the involucrata/wagneriana cuttings

Salvia involucrata grows very easily from cuttings.
Anything from the top 20 cm or so of a cane seems to grow, and I have rooted them in water or sand without hormone treatment. It would also grow from sticks broken off and pushed into the ground if the ground stayed moist. We planted some just-rooted cuttings roughly in a spot freshly cleared of overgrowth, gave them one watering and then watched as spring turned very dry and hot, but the cuttings just went dormant and sprouted again after rain, so they get the tick for hardiness.

The ease of propagation let me grow 20 or so to a good size to plant across the top of our dam wall. We had cleared this of lantana cover and needed something to colonise the bank in replacement. The involucrata has done the job well. As one side of the planting gets pretty much full sun I expected that this shade lover would suffer a bit, but it has grown well right across the planting and is looking nice as winter begins.

My plants also set seed, but I haven’t tried to germinate them yet.