Have you ever thought about how very few smallish evergreen shrubs there are with any longevity to speak of? If not, don’t. It might be best not to read on. It’s too sobering.
Indeed, evergreen shrubs in general are pretty poor at longevity. The best of them are rhododendrons, camellias, some of the laurels and some of the viburnums. These can easily outlast you. But they’re all large, if not huge.
I’ve been lead to this depressing reality by a recent obsession with Nicole de Vesian, thanks to Louisa Jone’s latest book (Modern Design in Provence, Actes Sud 2012), along with a need to think about plants that are capable of providing an evergreen matrix in which to plant lowish perennials, in prep for an upcoming workshop.
What I’m after are smallish shrubs, by which I mean in the 800 to 1200mm range. Most are short-lived. Think of lavender, cistus, rosemary and all that Mediterranean stuff. You’ll get five good years, and you may, at a pinch, in poor soils and with routine clipping, get 10. But no more. They’ll last this long, alright, but you’ll begin to wish they didn’t, as they become increasingly leggy, patchy and hollow.
There’s stuff like Pittosporum ‘Golfball’, but my experience with ‘dwarf’ or small forms of pittosporum is that they’re not so much small as slow. It feels like they take too long to get to a useful size, and next time you look they’re too big. I planted some ‘Silver Sheen’ with the intent of clipping them into balls. They were brilliant for four or five years, but after seven, they’re obese, and they’re totally intolerant of any serious slimming regime. They don’t recover from clipping back into leafless branches.
To be honest, about the only totally reliably long-lived evergreen I could come up with in this size range for my climate is box, either English (Buxus sempervirens), or Dutch (B. sempervirens ‘suffruticosa’), and these are going to need clipping for them to look their best, and to remain in this size range (or at least that goes for English box, which will eventually become a small, open structured tree if left unclipped).
Fortunately box is the evergreen shrub par excellence, being phenomenally long-lived, tolerant of being cut back to virtual stumps or skeleton if necessary, and unconcerned about being shaded or draped over by other planting for a season or so. Box is also very drought tolerant once established, though it does have a tipping point beyond which it simply will not recover, as those who’ve grown it in pots will attest. A single very hot, dry day can take it past this point, though you won’t know that it has tipped over the edge for several weeks, after which you’ll notice it start to lose it’s sheen and to assume a slight bronzy tint. It’ll be months before it actually looks entirely dead, though there’s no avoiding that outcome. Plants in the ground very rarely reach this point.
The only other smallish evergreen shrub that I could think of as having a several decade ‘best before’ date is Choisya ternata. This can get bigger than our agreed range – easily to 1.5 or 1.8m, but can be reasonably easily size-controlled, either with shears or secateurs.
There’s the straight species which everyone knows and takes for granted, or the fine-leafed form named ‘Aztec Pearl’, which is going from hard to find to harder to find. I notice that one of the big wholesalers has released a new one with fine leaves called ‘White Dazzler’. To be honest I can’t imagine being dazzled by a Choisya, and I’m not sure I want to be – it’s not what I grow them for – but I’ve yet to lay eyes on it, so should withhold judgement.
Along with the longevity thing, the other issue that raises its head when thinking of shrubs in a carefully height-controlled environment is the fact that shrubs actually don’t have an eventual size. Despite what the labels say, they don’t simply stop growing once they’ve reached some textbook dimension. They’re either growing or they’re dead.
No wonder, then, so many gardeners find the strap-leafed things so useful. Dietes, Lomandra, Phormiums etc continually renew themselves from the base, so are capable of maintaining a fixed (and reasonably predictable) height. Not that they’re entirely interchangeable with shrubs, but they offer an almost irresistible solution where you want a dome of evergreen foliage of fixed dimensions. Many, of course, share the ‘best before’ date issues of shrubs. I mean, is there anything more depressing than a six year old Lomandra? full of dead foliage and impossible to effectively groom.
(about 18 hours after posting this, it occurred to me that there are clear exceptions to the no-eventual-size rule of shrubs, being those that produce cane-like growth from the base (think hydrangeas, Philadelphus, Forsythia etc). But as it happens, nearly all of these are deciduous shrubs, and nearly all evergreens grow from peripheral growth so that they inevitably accumulate bulk, however incrementally. But more on this in some later post..)