There are no hard and fast rules when it comes to hedges, as the approach you take will depend on the climate and type of hedge. How, when and how often you prune will depend on a number of factors. If you have a winter or spring-flowering hedge such as camellia, avoid pruning it in autumn apart from nipping out the odd straggler.
Reboot an old favourite
It is the perfect time to plant new hedges or replant parts of existing ones. Planting now allows the plants to settle in before spring.
This season I'm focusing on taking stock of the hedges around our place. We have a manuka hedge at the front of our property which blossoms in October. But this year the growth has been a bit patchy. I clipped the hedge after it finished flowering in early summer and it took ages to green up again.
The hedge is more than 10 years old, and age, combined with two very dry summers, are likely to have made it more vulnerable to pests. On closer inspection, there were thick matted bundles of frass (caterpillar droppings) hidden in the branches.
These hid small but hungry "webbing caterpillars".
I recently pruned the hedge hard, sacrificing most of the spring-flowering growth. Two plants in the hedge have almost died and need replacing. We found large-grade bushy Leptospermum Karekare shrubs at Blackbridge nurseries to fill the gaps. Smaller-grade plants grow quickly and are a more cost-effective option, but we needed a quick fix as this hedge takes pride of place in the front garden.
Giving this hedge a hard prune will also make the environment less hospitable for overwintering caterpillars. I'll spray with Dipel, a product which utilises bacteria for organic, biological caterpillar control. Bald spots in hedges can be camouflaged by tying branches into place. Another hedge in need of attention in our garden is the Lonicera hedge, which I've grown from cuttings.
Lonicera is super-easy care and very easy to propagate. It serves the same function as formal box hedging but is much faster growing. Parts of this hedge have succumbed to dog traffic, so I've replanted those spots with year-old rooted cuttings, as well as moving some established plants to fill the larger gaps. After planting I cut the lot down to around 30cm, which will rejuvenate the hedge with new spring growth.
When to chop
It is okay to give hardy evergreens a prune now if you have a frost-free, milder climate, particularly if you want to replant parts of it (or wait until spring when the hedge is growing more vigorously). A dry day in winter is the best time toprune deciduous hedges or shrubs. Remove any diseased or broken branches and aim for a slightly tapered shape to allow light to reach the lowest parts of your hedge.
If you are not such a dab hand with hedge clippers, use a string line as a guide and regularly stand side-on to look along the line. Ensure your tools are sharp and oiled so they cut cleanly and efficiently. Wipe off sap with an oily rag to reduce drag (I use old vege oil).
To renovate a woody or overgrown hedge, it is best to prune in stages to avoid stressing the plants too much. The Royal Horticultural Society recommends pruning one side one year, then the other side, then the top -- so a three-year commitment to give an old hedge a reboot. However, much of the North Island has a more inclement climate than the UK, and many of us plant fast-growing native plants for evergreen hedging. Most of our native hedging species such as griselinias, coprosmas and corokias will stand a hard once-over if needed. Hardy evergreens such as feijoas can be cut back almost to a stump and will sprout away next season.
Feeding and mulching time
Feed your hedge, permanent shrubs and trees with a slow-release organic fertiliser to nourish and remineralise the soil. Good options are basalt rock dust with added goodies such as seaweed and beneficial bacteria such as Environmental Fertiliser's General Fertiliser or Agrissentials Rok Solid.
When planting, add Trichopel or Dalton's Bio Fungicide to insure against soil fungal invasion of the bad sort. Applying mulch afterwards will prevent the soil from leaching nutrients in high rainfall.