All hedges need to be trimmed once a year. This includes Leylandii hedges as well as Laurel, Portugal Laurel, Box, Yew and Privet. If you keep your hedge to a reasonable height, it doesn't take long with a good hedgetrimmer. If you think how many times you cut your grass a year, trimming a hedge is much less work and it is much easier than painting a fence that will fall down after a few years!
Trim your Leylandii hedge once (or at most, twice a year). Some people recommend trimming it three times (or more!) a year but this isn't necessary and, in fact, can weaken the Leylandii hedge especially in years of drought or during other forms of stress. Leylandii hedges that are trimmed too many times do not get a chance to put on any re-growth before the spring, so they are more likely to suffer from problems.
If you do not trim your Leylandii hedge each year, it will grow up to 3ft (90cm) a year and quickly get to a height where you need to call in a professional tree surgeon or get specialist equipment such as hedge cutting platforms. If you keep your hedge at a height of 6-8ft (2-3m), it is much easier to trim than if it is 10-15ft (4-5m) in height.
We trim most of our hedges once a year. We do have tall hedges that are 12ft tall (4m) and we use a Henchman Hi-Step Platform to reach these hedges. These Leylandii hedges provide an excellent windbreak for our polytunnels.
Always leave about 4 inches (10cm) of green foliage on the hedge, before you get to the brown wood inside the hedge. If you cut it really hard back so there is barely any green foliage left on the hedge, you are likely to get problems if the plants undergo any type of stress, such as hot and dry conditions that can scorch the foliage or reduce the capacity for the hedge to re-grow.
Trim your Leylandii hedge back to the same height and width every year - you can see where it was trimmed the previous year - this ensures it stays the same height and width and doesn't grow taller or wider each year. Try and leave your hedge slightly wider at the bottom than at the top.
Trim your Leylandii hedge in the spring or summer months. This gives the hedge a chance to recover and put on a bit of re-growth before the winter but try to avoid trimming your hedge during periods of very hot or dry weather. Also, recent research has shown that trimming your Leylandii hedge in late autumn can possibly make it more susceptible to winter attack from Cypress Aphid. However, watch out for nesting birds from March to July, as it is illegal to disturb nesting birds.
You can trim your hedge with a sharp pair of shears or a hedgetrimmer. Make sure the blades are sharp on your hedgetrimmer so it cuts the branches rather than ripping them off. Clear off any trimmings from the top of the hedge (we use a leaf rake to do this), if you leave them on, they will rot and can cause disease.
If your hedge is on a boundary with a neighbour, they should be consulted as their side of the hedge will need trimming. If you are planning to plant a new Leylandii hedge, consult them first and know what your plans are and how tall you intend to keep the hedge. If they are unwilling to trim their side of the hedge, make sure you can reach it from your side before planting the hedge.
Remember that it is your responsibility to maintain the hedge if it is on your property. The Anti-social Behaviour Act (2003) allows councils to take action if you allow your hedge to grow to a height where your neighbour's "reasonable enjoyment" of their property is being adversely affected. Additionally, you are also responsible for any damage that may occur if you allow your hedge to become overgrown. See our section on Leylandii Law for more details.