Elegant silvers

Sunday, 25 March 2012

Helichrysum petiolare

Recently going through all my gardening books in order to donate some to a big sale planned in May by the Friends of the Botanic Garden, I came across one entitled Elegant Silvers. I realised that though I had previously written a blog about silver plants that grow in the shade, I had never done one on those that thrive in sunny spots. I have always loved silver-foliaged plants, as they provide such an effective light and sheeny contrast to the multitude of often ponderously green leaves in the garden, giving colour all year round. They look beautiful as companions to blooms of many hues: but my favourite flower colours for combining with silver are white, cerise, blues, pinks and purples. I also love the dramatic contrast of silver leaves grown nearby to deep purplish-black foliage and/or flowers.

The silver colouration on leaves usually comes from the adaptation by the plant to hot, dry conditions, and this often means that the leaves have an interesting texture as well as an attractive colour. For example, a number of them have leaves covered with a protective layer of down or hairs that reduce transpiration and reflect away infrared radiation. Others have a surface wax on the leaf surface to perform these functions. They often come from deserts and dry, stony areas, especially in Mediterranean Europe and South Africa. This means they are so useful for growing in hot, dry positions in our gardens: places where many other plants fail to thrive, but also means that they may be relatively short lived in our humid climate, especially in a wet summer such as we have just experienced. However, most will give a few good years of service and are easily propagated from cuttings, and some are actually quite unfazed by the weather and last for many years.

Stachys byzantina

There are a number of perennial plants with silver leaves. Two 'cottagey' ones that do well here are lambs' ears (Stachys byzantina) and Lychnis coronaria. Both are low growing, with basal rosettes of textured leaves. Lychnis coronaria has the bonus of very pretty spires of cerise, white or pink-eyed white blooms in late spring and summer. I find that both these plants may rot off after a few years and the best way to prevent this is to divide them up regularly. Congestion of the plants seems to promote fungal problems in the foliage. Both plants associate well with Mediterranean plants such as lavender, tall bearded Iris, rosemary and marguerite daisies.

Artemisia arborescens

A surprising number of silvery plants come from the Asteraceae (daisy) family, including the South African groundcoverers Gazania and Arctotis, which have cultivars with metallic-looking foliage. They thrive in well-drained soil and have large daisy blooms over a long period in spring and summer. Taller, more shrubby perennials include many of the genus Senecio, with deeply cut, decorative foliage, which provides an effective contrast to plain green leaves in a border. I have had various specimens over the years that I enjoyed, including Senecio viravira (ht 60 cm) and Senecio cineraria (ht 60 cm), though at the moment, I don't have any in the garden. They may bear daisy-like blooms, but I never found these very appealing and used to trim them off. A plant that I recall growing years ago was Tanacetum ptarmiciflorum (ht 60 cm) - its delicate silver filigree foliage almost seems unreal. I would like to grow it again one day. Artemisia arborescens, sometimes known as wormwood, was an old favourite of mine in my first garden. It has lovely feathery, silky leaves, with a strange yet likeable musky smell, and grows quite tall (up to 1.2 m). Later I grew the compact cultivar Artemisia 'Powis Castle', which grows to around 60 cm tall, and it is a very good foliage plant. Note that some of clump-forming types, such as A. ludoviciana and its cultivars can become invasive, and should be avoided. South African Helichrysum petiolare (ht 60 cm) has small, heart-shaped leaves that look as if they have been cut from silvery velvet cloth. Growing from a woody centre, it sends out long stems that wander through other plants and can cover a fair bit of territory. Unlike the rest of the silvery Asteraceae plants mentioned here, it will grow in part shade as well as full sun. All these shrubby Asteraceae plants do seem to need to be cut back every so often to stop them becoming straggly, and I have found that most of them only lasted a few years. However, they are very easy to grow from cuttings.

Strobilanthes gossypina

Strobilanthes gossypina (ht 1 m) is another plant with beautifully textured, felty, silver leaves. It forms a domed shrub up to about 1 m in height and will tolerate sun or part shade. It is a member of the Acanthaceae family - and though its lilac flowers are lovely, it is really best to hope that it never flowers (which is often the case) as it tends to drop dead after the floral display is finally over! Mine did this last spring, and I am still mourning its departure and hoping to find a new specimen in a nursery somewhere.

Salvia discolor

Salvia discolor is probably the only Salvia I have with silver leaves, as the other varieties don't like the Sydney humidity - even the common old edible sage (Salvia officinalis), which often drops dead overnight. Salvia discolor is a rather sprawling specimen (ht 1 m) with rather sticky-feeling silver leaves and stunning navy-blue to black flowers almost all year round. It seems incredibly drought tolerant and is one of my favourites of the genus. It has proved to be a long-lasting plant. Also long lived are some Buddleja with attractive silver leaves and one of the very best is the cultivar 'Lochinch' (ht 2.5 m), which also has pretty lilac flowers in late spring and will repeat-bloom through summer and early autumn if it is deadheaded regularly.

Finally I must mention Plectranthus argentatus (ht to 1m), which is just as happy in sun as in deep shade. Its large leaves can provide a large pool of silver in any border and remains one of my all-time top plants. There are some compact cultivars, such as 'Silver Shield', but I tend to pinch back all my specimens regularly to keep them shapely, and they survive a long time.

There are lots of candidates for 'elegant silvers' in Sydney gardens!