Silver foliage shrubs for the winter rock garden

Silver leaved New Zealanders

Celmisia haastii

This is one of my favourite silvers that keeps it brightness the whole year through. It is a member of a large Australasian (chiefly New Zealand) genus of daisies that are very prominent in the montane flora. The climate of the mountains of New Zealand rather resembles that of Scotland or Ireland. So it is no surprise that they thrive best in the cool, moist climates of the west and north of the UK.

Placement and planting

The chief requirement of this and many other celmisias is that the soil does not dry out in hot dry spells. This is aided by planting in rather heavier soils than for most alpines, and watering if necessary. I grow my best plants in a semi-shaded raised bed at the foot of a sloping lawn. Water drains from the lawn into the bed which as a result remains moist in all but the longest droughts.

Propagation

Celmisias occasionally set viable seed in UK gardens, but it is very much the exception rather than the rule. Mostly the ‘seed’ has no embryo and is mere chaff, viable seed is hard and plump. If you do get seed and have several species growing close together it is likely to produce hybrid offspring. Indeed, I often find self-sown seedlings that are clearly the result of hybridization.

So if you want ‘true’ celmisia species you will need somehow to get viable seed from New Zealand. Fortunately, some thoughtful NZ members of the AGS contribute wild collected seed to our exchange. As the viability of celmisia seed is short-lived, be prepared for failures in either event. Alternatively, vegetative propagation of most celmisias, including Celmisia haastii is quite easy. Accordingly, plants of this and other species are available from specialist alpine nurserymen. If you have plants, take cuttings from the outside in late spring, place them in a pot of humus-rich but well drained compost, water well and place in a shaded frame. Make sure they never dry out, and don’t be too eager to pot them up. If necessary you can leave them in situ until the following spring.

Ozothamnus plumeus (syn. Helichrysum plumeum) and O. coralloides (syn. Helichrysum coralloides)

Two other closely related New Zealand silver-leafed alpine shrubs are among my favourites. Both are long-lived, having been permanent fixtures in our garden for 40 years. They are the well named ‘coral plants’, Ozothamnus plumeus and O. coralloides.  In that time the former has never flowered, and Ozothamnus coralloides only occasionally. Which is no loss as the flowers in each case are tiny insignificant daisies. These only serve to spoil the symmetry of these architectural plants. They will stand more drought than Celmisia haastii and are altogether more forgiving, not requiring any attention once established.

Propagation

I have never seen seed offered but would not bother with it anyway. Semi-hardwood cuttings root easily if slowly in a gritty medium with some organic matter. Keep them shaded and do not allow to dry out.

Euryops acraeus

This is another Southern Hemisphere daisy bush, but in this case from the Drakensberg Mountains of Lesotho and Natal (South Africa). It is a true mountain dweller, its specific epithet meaning ‘dweller in high places’.

E. acraeus forms a slow-growing, rounded evergreen bush. The foliage is intensely silver throughout the year, making it particularly valuable in the winter rock garden. The flowers, which appear in late spring, are c. 2.5cm across, bright canary yellow, making a good show for several weeks. It is best to remove them as soon as they fade so that the dead flower stalks do not detract from the symmetrical character of the plant for the rest of the year.

This is an easy plant to grow, requiring only a sunny spot in gritty, sharply draining soil. If it gets a bit lax, trim it back into shape, but this is unlikely to be necessary for a good many years. You might think that coming from southern Africa it would not be hardy, but because of its montane origins E. acraeus is unlikely to suffer in any but the most severe frosts.

Propagation

I have never tried to grow E. acraeus from seed, partly because it is very easy to increase from cuttings of semi-ripe wood taken in July/August. Indeed, if the base of the plant is buried to a few centimetres deep with gritty compost, some of the covered shoots are likely to produce roots. These so-called ‘Irishman’s cuttings’ can then be removed and potted up.

Artemisia ludoviciana ‘Silver Frost’

This is a selected compact, non-suckering form of a species that is very widely distributed in N. America, from Canada to Mexico. It is essentially a hardy evergreen, but may loose some of its leaves in particularly wet, cold weather. Thus, in the garden you should plant it in the hottest, driest position available. Unlike Euryops acraeus, you will need to clip it over frequently to maintain its shape and prevent it becoming lax and opening up. Tiny ‘mugwort’ flowers are produced in long spikes in late summer. Remove them promptly as they detract from the silvery sparkle for which we grow the plant.

Propagation

Like all artemisias, A. ludoviciana ‘Silver Frost’ is simplicity itself to propagate from cuttings taken at almost any time. Cut non-flowering shoots neatly, remove any leaves that would be buried in the rooting medium, insert to c. 4 cm, water, leave in a semi-shaded situation. You may well have rooted cuttings suitable for potting up or planting out within a few weeks.

Ptilotrichum spinosum roseum

A shrubby candytuft from the high Atlas mountains rounds off this short selection of silver-leafed shrubs for the autumn garden. This bone hardy prickly dome covers itself in posies of tiny candytuft flowers in spring, but it looks good throughout the year. Tumbling down a wall, as shown here, is a good place for it, but any well drained, sunny spot will suffice. I know of no other plant that I have had for >20 years that has demanded so little attention. It has never been pruned, fertilized, or watered!

Propagation

I have had occasional seedlings turn up in the gravel path beneath the plant shown, and they are easy enough to lift and grow on. Cuttings of the new growth taken before the spines harden root quite well in very gritty compost.

Pests and diseases

I have never noticed this plant being attacked by any pests or diseases, bomb-proof is the term that comes to mind.

John Good

Our author is a retired research forest ecologist and Emeritus Professor of Environmental Forestry at Bangor University. Throughout his life, John has been interested in all aspects of the observation and cultivation of plants. Alpines and woodlanders were always of particular appeal. He has called North Wales his home for more than 40 years. John and his wife, Pam, have developed and enjoyed their current hillside garden overlooking the sea for the last 27 years.

He joined the AGS over five decades ago. During this time John has served as AGS Director of Publications, Assistant Editor of our journal and as judge at our shows. After years of serving on the RHS Joint Rock Garden Plant Committee, he is now a friend.

John has travelled and lectured widely on alpines and written many articles and several books on the subject. He has also always been heavily involved in his local North Wales Group.