The general rule for shrubs is to prune just after flowering. But, if you want to retain fruit to feed the birds, especially on shrubs like pseudopanax and coprosma, delay trimming until the fruit has gone. Do not postpone pruning until late autumn or winter, because soft regrowth will be damaged by frost.
Sharp secateurs are the best tool to prune large-leafed plants, while hedge clippers are ideal to trim fine-leafed shrubs. Stand back regularly while you are pruning to make sure you are retaining a symmetrical, natural-looking form, not straight sides or an ugly flat top.
In this article I will concentrate on the native species I most often see spoilt for lack of an annual trim.
Coprosma cultivars are available in an enormous variety of foliage colours. The brightly coloured, shiny leafed cultivars are most useful plants for providing colour contrast and texture in the garden. Some of these plants will eventually grow to 1.5m-2m high, but they rarely look attractive at this size. If you tip prune them annually you can keep them to a compact 1m-tall shrub.
Prune in early autumn or late spring to minimise frost damage to regrowth. It is also a good idea to tidy the plant by removing the profuse dead branchlets it tends to retain. New shoots are soft and easily broken, so be careful when pruning not to damage branchlets you want to keep.
Shiny leafed cultivars like ‘Middlemore’ and ‘Yvonne’ (photo 1) can be trimmed to form lovely hedges. Shorten branches to the desired length by making a cut about 5mm above the base of the opposite leaves (photo 2).
Griselinia lucida (akapuka) has large, lush, tropical-looking leaves. If it is pruned annually it will form a very attractive, densely foliaged shrub (photo 3) suitable for small gardens.
Griselinia littoralis (kapuka) has smaller leaves and is most often used as a hedge plant, but can just as easily be trimmed to form an attractive shrub.
If they are not pruned, both species will eventually grow into multi-stemmed small trees.
Muehlenbeckia astonii is a particular favourite shrub of mine. I love its fine, wiry, red-brown branchlets tiny, bright green leaves in summer and the way it holds sparkling raindrops suspended in its foliage. It is also a host plant for caterpillars of the beautiful little native copper butterfly.
Without trimming, this species grows to form a rather lop-sided plant. It tends to send out a few thick, strong stems (photo 4) that eventually give the plant an asymmetric shape. My remedy is to cut these thick stems well back into the centre of the plant. You are then left with fine, wiry stems, easily trimmed with hedge clippers. An annual clip in autumn will keep it looking good. You can also shape it into formal balls as seen in the Auckland Botanic Gardens (photo 5) or use it to create an unusual hedge.
Manuka (Leptospermum) hybrids and cultivars produce masses of tiny, colourful spring flowers. They also benefit from an annual trim after flowering to maintain a compact shape and reduce their tendency to form tall, woody plants, holding their flowers only on the ends of long branches.
Often hebes are not long-lived plants in the garden, but are loved for their abundant, bee-attracting flowers. They are frequently spoilt by a lack of trimming. If the dead flower heads are removed straight after flowering and the foliage cut back by about one third, you can stop hebes from becoming woody, sprawling plants.
Always leave foliage on a stem if you prune back to bare wood, the stem usually dies.
Lophomyrtus x ralphii ‘Kathryn’ has attractive, small, purplish brown, shiny leaves that make it useful for textural and colour contrast in the garden. It will grow to 2m high, but tends to become lanky and leafless as it grows taller. An annual clip will keep it compact. It will also recover from a very hard pruning.
Many Pseudopanax lessonii (houpara) hybrids and cultivars are described and illustrated on the T.e.R:R.A.I.N website (www.terrain.net.nz). ‘Cyril Watson’, ‘Purpurea’, ‘Trident’ and ‘Goldfinger’ are a few examples of the wonderful foliage plants available in this species. They respond very well to pruning. If they are not pruned annually, especially if growing in part shade, they tend to lose all their lower leaves and produce foliage high on a 2m-3m plant, on which their beauty goes to waste. Their large leaves make them unsuitable for a tight formal hedge, but they can easily be pruned into an informal hedge or a tall pleached hedge.
Although pseudopanax flowers have tiny green petals and no obvious scent they are very attractive to insects. My mature
P. lessonii ‘Cyril Watson’ buzzes with native bees and honeybees in January (photo 6). The berries are good food for the birds. I recommend pruning pseudopanax in early autumn. In spring you will be removing potential flowering branchlets in midsummer cutting off the outer foliage will lead to the softer leaves underneath scorching in the sun (photo 7), and in late autumn and winter the regrowth will inevitably be damaged by frost. Trim stems back to 5mm above a leaf base to avoid leaving an ugly stick that will die back (photo 8). The young foliage of P. lessonii ‘Purpurea’ turns a beautiful deep maroon colour in cool weather. If you prune it in early autumn you can maximise this colour all winter and well into spring (photo 9).
If a shrub does become frost damaged it is best to leave the damaged foliage on the plant until all danger of frost has passed. The dead leaves help insulate the foliage underneath, providing protection from further frost damage. If you delay pruning until new growth appears in spring, you will see clearly how far to cut back the damaged stems.
Pruning every year might not be necessary in the cooler parts of the country, but it certainly is in milder areas like Auckland. Set a reminder for yourself in your garden diary or on your computer so you do not forget to complete this easily overlooked task. You will be surprised at how good well-pruned native shrubs look.