When you’re starting out with hedge trimming, you might not know how far you can cut back a shrub before killing it. I thought I’d shed some light on much you can prune from a plant without harming it.
All hedges are living things and will grow back if you are careful with your cutting. As long as you have not fundamentally damaged their structure, you can help them recover from being cut back and they should respond well to occasional pruning and trimming.
There are a few obvious dos and don’ts with hedge trimming and if you follow the basic principles, your hedges will survive your efforts to keep them in good shape. Let’s find out more!
What Is A Hedge Made Of?
A hedge is a living being; a plant whose main components are roots, branches and leaves. Hedges can be either evergreen (holding on to their leaves throughout the year) or deciduous (shedding their leaves, usually in the Winter).
When a hedge is newly planted it will spend time establishing its root network, making sure that it can derive essential minerals from the ground. Once this has been achieved, it will grow branches that contain leaves and over time these can become big and bushy; hence the need for hedge trimming.
Over the course of a year, a hedge plant will focus on either growing roots or growing shoots, and the effect and timing of your trimming and pruning will impact on it’s success and overall health.
How Far Can You Cut Back A Hedge?
The rule of thumb for trimming hedges is to cut back no more than a third of the total volume of the hedge at one time. This is enough to encourage new growth in the top half of the plant without causing serious damage to its overall wellbeing.
If you want to trim your hedge, it is a good idea to spend time looking at the plant to understand how its growth has happened, so that you can cut back specific areas without harming the underlying structure of the plant. Most hedges will have an inner skeleton; a thicker structure that supports the smaller branches and leaves, and unless you are hard pruning a plant, you leave this skeleton alone.
The aim of trimming the hedge is to cut back unwanted growth, with the aim of promoting new leaves and maintaining a nice shape. If you trim your hedge in the Spring, it will encourage the plant to grow new shoots and leaves in the Summer, which will lead to denser foliage and better overall health for your shrubs.
What Happens If You Trim A Hedge Too Much?
If you cut back a hedge too far, you can jeopardise its ability to grow new leaves and shoots in recovery. This can starve the plant, destabilise its hormonal balance and even lead to plant death.
Plants use hormones to grow and they have two main types of hormone:
Cytokins are the hormones that stimulate root growth, while Auxins support the growth of buds and leaves. In a healthy plant these are in balance, allowing the plant to focus on root growth in the Winter and leaves in the Spring and Summer. If you cut back a hedge plant you can prevent Auxins from fulfilling their function in growing new shoots, which impacts on the amount of Cytokin activity, leading to impaired root growth, which can then lead to less Auxin production in the following year. It’s a hormonal snowball effect that can have lasting damage on a plant’s wellbeing.
Cutting back your hedge too much can also prevent the plant being able to derive energy from the sun, causing it to become malnourished. Plants convert sunlight to energy through photosynthesis and if you remove too many of their solar cells (leaves) you can starve your plant of the energy it needs to survive.
Can You Kill A Hedge By Trimming It?
You can kill a hedge by cutting back its structure beyond the point of repair. If you trim the hedge in the autumn or winter, this will increase the risk of fungi or other infections that may also kill the plant.
These are both easily avoidable outcomes. You should only ever trim hedges in late Spring or early Summer so that they can benefit from the warmth of the seasons to thrive. The increased hours of sunlight and beneficial ecosystem – the birds, bees and other creatures that use hedges – will all work to support the growth of the plant.
If you carry out maintenance to your hedges in the wetter months, you deprive the plant the chance to dry out and to repair. Shrubs are often at risk from fungi and other invasive species throughout the year, but a healthy plant will have a good chance of standing up to such threats. However if a plant is trying to recover from a pruning without having sufficient energy from the sun, or it is continually damp, the chances of succumbing to infections are greatly increased.
Once a fungal infection gets into a hedge plant it can be difficult to clear, and if it affects the skeleton of the plant, it can be very detrimental. You also run the risk of the infections spreading to other plants in the wetter months, which can be disastrous for your hedgerows.
It is a sad day when a hedge dies, particularly if you enjoyed it’s presence, and so some care and attention when trimming will go a long way to preventing this tragedy. I’ve written a guide to hedge trimming that covers all the basics, so you can take care of your hedgerows with confidence.
If you aren’t sure when you should trim your hedges, I’ve got you covered there as well!
How Can You Repair A Hedge That Has Been Damaged?
It will take time to repair a damaged hedge, but if you protect the damaged areas against the weather, and establish a regular feeding/watering schedule, most hedge plants will return to good health.
Assuming that the damage has not destroyed the underlying structure of the plant, and that there are areas where leaves are growing, then you can use fleece to protect the most hard-hit parts of the plant from cold and wet weather. This will give the plant a chance to dry out and harden, a necessary step to ward off fungal infection.
All plants benefit from feeding and watering, and while nature can do most of that work, if you use appropriate fertilisers at the base of the plant, this can support the roots in providing additional hormones and energy to encourage the recovery.
For a more detailed answer, be sure to read my post on how to revive a dying hedge.
What Tools Can I Use To Trim A Hedge?
You can achieve most of your hedge trimming goals with a good pair of garden shears and a pair of secateurs. If you have a lot of surface area to cut back, a powered hedge trimmer will come in useful, but if you are budget conscious you may choose to hire one, rather than buy it.
I’ve written a few posts that can help you in this matter, but the guide to budget hedge trimming tools is a great place to start.