Silver in the sun

Sunday, 06 March 2016

Arctotis hybrid in the garden of Dominic Wong in Mittagong NSW

The unrelenting heat of the last few weeks in Sydney has turned my thoughts towards tough, sun-loving plants, and some that come immediately to mind are silver foliage plants, as the physiological features of the leaves that makes them look silvery are usually adaptations to cope with extremes of heat (and cold in many cases) - such as a protective layer of down or hairs, or a waxy coating of powdery 'bloom' or 'meal'.

Stachys byzantina performs quite well in Sydney if divided up every so often

Silver foliage adds an extra dimension to the colour scheme of a garden - adding a sparkling light to borders, and mixing particularly well with white flowers, as well as pinks, blues, purples, cerise and burgundy. I also like the dramatic contrast of silver foliage with sultry purple and near-black leaves and flowers. I am less likely to pair silver foliage with hot colours myself, but it can be done!

Not all sun-loving silver foliage plants like our climate, however. The high humidity of our summer weather is disliked by many of them: they may grow well for a while but then start to rot off due to fungal diseases as the humidity rises, especially in February. Our heavy summer thunderstorms can also often spell doom for some of these sorts of plants. On the whole, they come from Mediterranean-like climates with hot, dry summers and cold winters. A quick survey of my garden revealed those that I would term the survivors. Even with these, I have struggled for a while to work out how to grow them best.

In general, I have found that sun-loving silver-leaved plants need good drainage and space around them. For this reason, I tend to grow mine in raised beds, and usually on the edge of the bed, rather than in the middle of it, to avoid the plants being swamped by their neighbours. Possibly having other plants too close raises the humidity around the plant. Being on the edge of a retaining wall allows the plant to spill forward over a hard, heat-retentive surface, avoiding having too much damp soil around its base. Clump-forming silver-leaved perennials should ideally be divided every few years, to avoid having too much foliage, which can also create humidity (and hence fungal diseases) around the plants. Overwatering of the plants should be avoided for the same reason. The soil in which the plants are grown should not be too rich in organic matter; a more lean, gritty soil seems to suit them better. These are only my theories, but they have helped me grow my silver plants more successfully.

Buddleja crispa

I always dreamed of growing a silver pear tree, just like at Sissinghurst, but they don't really like Sydney's climate so I have been content instead to grow a few different Buddleja with silvery foliage instead. The best one I've found is Buddleja crispa (ht 2-3 m), with large, triangular leaves like pieces of silver felt. It does have pink flowers in summer, but its main attraction is the foliage. It makes a good background shrub, but don't let it be crowded by other plants. Another good silver-leaved Buddleja is the cultivar 'Lochinch' (ht 2.5 m), with handsome silver-grey foliage. In this case, the abundant lilac flowers are a definite feature and it will rebloom through summer if the spent flowers are removed. The cultivar 'Silver Anniversary' (ht 1.5 m) is a smaller, white-flowering plant that has Buddleja crispa as one of its parents, and is worth growing in more compact spaces.

Artemisia Powis Castle (left) with Plectranthus argentatus

A lovely silver plant I have only recently had luck with is Artemisia 'Powis Castle' (ht 60-100 cm), one of the best specimens in this genus, some of which can be invasive. It has highly dissected, silky, aromatic leaves and should have been an asset in a sunny border, but I always found it rather shapeless and lanky: it never made the dense mound of foliage in the middle of a border that I saw in English gardening books, and I always seemed to be cutting it back to try to make it more bushy. A breakthrough came when I decided to grow it over the edge of a sunny retaining wall. It looks so much better in this spot, flopping forward in a good way and not being hemmed in by other plants. I have also taken to tip pruning it to encourage a denser form, and this has helped. I enjoy pairing it with the broad silver leaves of Plectranthus argentatus, an agreeable shrubby perennial that will grow in sun AND shade. There are some more compact forms of this Plectranthus around these days: the original species can get a bit tall after a while.

Dichondra argentea Silver Falls growing on the edge of a brick path in my Sydney garden

Dichondra argentea 'Silver Falls' is a groundcover I never had any luck with until I planted it at the edge of a garden bed. It promptly climbed over onto the side of the adjacent brick path, where it is simply flourishing in the hot and well-drained conditions. I love its dainty, rounded, silvery leaves, strung together on long stems. It has softened the hard surface of the bricks in a way I could never have planned or even imagined! I don't know how this will all end: perhaps it intends to take over all of the paving in the garden? At the moment, the effect is quite charming.

Others that I have had success with are Stachys byzantina (which will sometimes rot off in parts after a lot of rain in summer, but enough usually remains for it to regrow over winter; it will benefit from regular division); Helichrysum petiolare (another silver-leaved plant that will also grow quite well in sun or shade, and which looks fantastic spilling over a retaining wall, as pictured above); Lychnis coronaria (now correctly known as Silene coronaria, with stunning magenta or white flowers in spring, above a basal rosette of felted silvery foliage that needs to be split up every year or so); forms of Gazania and Arctotis (daisy-flowered groundcovers that do so well in our climate); and a number of succulents, including the pretty Kalanchoe pumila 'Quicksilver' and many Echeveria. My failures include Convolvulus cneorum, lavenders, Dianthus, Cerastium tomentosum, Echinops, Eryngium, Perovskia atriplicifolia ... and many others! Those living in less humid climates with cooler winters will doubtless have better success than me with these lovely plants!