Establishing a Leylandii Hedge

Keeping newly planted Leylandii watered

After planting, it is important to make the your leylandii trees get enough water and that the roots never dry out.

If you plant between November and February, a your Leylandii trees will need less water (or maybe even none at all). However, you can plant container-grown (pot-grown) Leylandii from March to October without a problem as long as you water them throughout the spring, summer and autumn (but not in the winter). Keep an eye on them from February to October to make sure the roots don’t dry out. After they have been growing for a year, they generally do not need watering again as their roots will grow to take up the water they need.

How to water your Leylandii

Firstly, check they need watering by pushing your finger into the rootball of the plant or into the soil next to the rootball. This should be done every 2-3 days for the first year (spring, summer and autumn). The soil wants to stay moist but not soggy or waterlogged.

In general, your new Leylandii trees will need a good soak once or twice a week, every week (maybe more in very hot and dry weather) but this will depend on the weather conditions and your soil type. If you go away for a couple of weeks during the summer, make sure you have an automatic irrigation system and/or someone reliable to water them while you are away. If not, you could come back a find them all dry and crispy!

You can water using a hose or watering can but make sure you water the soil around the rootball until the water starts to run off, then move on to the next plant aƒnd work your way along the hedge. To make sure the water has sunk in, you should go back to each plant 3 to 4 times – give the water a chance to sink in to the soil before watering each plant again.

Alternatively you can use an irrigation system such as Porous Pipe (leaky hose). This is good as it allows the water to sink into the soil at a gradual rate. As a general rule of thumb, water them once a week for about 2-3 hours with Porous Pipe – up this to two or three times a week during very hot and dry weather. Remember to check that they need it first as it is easy to overwater Leylandii with irrigation systems.

Never assume that just because it has rained that your Leylandii have had enough water. Often rain in the spring, summer and autumn months is not enough to provide enough water to the roots. If you buy a rain gauge, you will know how much water they are getting from the rain. As a rule of thumb, Leylandii need about inch (6mm) of rain to keep them watered for a 2-3 days during the summer months. If you are getting less rain than that, you will need to test the soil to see if they are drying out.

Don’t leave it until your Leylandii look like they are wilting or suffering from drought before you water them.

Watch out for drought symptoms

When Leylandii are too dry or too wet, their needles start to turn yellow and then brown. This starts at the base of the plant, near the trunk and works its way upwards and outwards.

The symptoms of drought are normally caused by lack of water but can also be caused by too much water (waterlogging). This often occurs when people leave irrigation systems on too long or when Leylandii are planted in small holes in heavy clay. If you have a heavy clay soil, make sure you break up the soil when planting Leylandii so any excess water can drain away, otherwise you can create a clay bowl for the water to collect in.

The roots of Leylandii will rot when they sit in waterlogged conditions for extended periods of time. This will mean your Leylandii cannot get enough water to the foliage and they will look like they are suffering from drought when they are actually too wet.

How to establish a Leylandii Hedge

As soon as you have planted your Leylandii trees, you can start trimming any branches that come out wider or that are taller than you want the hedge to be. If you imagine the shape you want your hedge, trim off any branches that protrude out of this shape. This will encourage shoots to grow within the hedge and will ensure the hedge thickens out quickly.

When the height of your Leylandii trees grow to within 6 inches (15cm) of the height you want your hedge to be, trim off the tops. This will also help the plants thicken out.

Twice a year, or more often when the hedge is establishing, trim off any shoots coming out of the hedge or growing taller than you want the hedge to be. The hedge will start to thicken up and form a good screen.

Once the hedge has established, you need only trim once a year.

Trimming & Maintenance

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!

Trimming and Maintenance of a Leylandii Hedge

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.


In general, Leylandii are disease free. However, here are a list of diseases that can occasionally effect Leylandii.

Pestalotiopsis and Botrytis (Grey Mould)

Pestalotiopsis and Botrytis are fungal diseases that are spread by wet conditions. It generally only infects plants that have been weakened in some way, such as attack those trimmed too often or too hard, particularly late in the autumn. Under the right conditions, Pestalotiopsis and Botrytis can affect many plants including conifers and Leylandii.

In the past, diseases such as Pestalotiopsis and Botrytis were only found rarely on production nurseries where plants were grown very close together with overhead sprinkler irrigation making the leaves wet every day. There is evidence, however, that over-enthusiastic trimming of Leylandii creates a lot of dead material or “thatch” in a hedge. This thatch can act like a sponge and hold water, keeping the hedge wet for extended periods of time. The occasional attacks by Cypress Aphid can also make disease more common in hedges so it is important to check Leylandii hedges for Cypress Aphid in January or February and take action if they are found (see below).


The symptoms of Pestalotiopsis and Botrytis are the tips of the shoots turning brown and dying back causing random brown patches. However, these symptoms can also be caused by a number of other factors including Cypress Aphid, a blunt blade on a hedge-trimmer or trimming at the wrong time of the year.


Plant Leylandii properly (follow our instructions) so their roots get established well.

Avoid trimming in very wet or very dry conditions.

Trim from early spring to early summer.

Trim once (or twice a year). We do not recommend trimming more than twice a year.

Remove all dead material and “thatch” from a hedge after trimming using your arm or a rake or brush.

There are no fungicides recommended for specific use against Pestalotiopsis but products such as Sythane Fungus Fighter and Fungus Clear Ultra may be used at your own risk.

Check for Cypress Aphid in January and February every year and spray with Scott’s Bug Clear Ultra or Bayer Garden’s Provado Ultimate Bug Killer if they are found.


Honeyfungus is a common fungus that is often found in the soil. It attacks the roots of most plants including conifers and Leylandii. No plants are immune from attack but some are more tolerant than others. Privet hedges are particularly susceptible to the disease.


If whole plants within a hedge are dying and, over the years, the symptoms are spreading to neighbouring plants in the hedge, it is possible that the hedge is being attacked by a soil borne disease such as Honeyfungus.

Honeyfungus spreads through the soil by black bootlace structures called Rhizomorphs. These can be seen in the soil but can be difficult to spot.

Examine dead material by scraping back the bark near the soil (up to 1 metre from the soil surface). If this reveals a white layer of fungal-like growth that smells strongly of mushrooms, then it is likely that it is honeyfungus.

Infected roots are dark brown or black.

Clumps of honey-coloured toadstools appear near the hedge.


Unfortunately, there is no chemical control.

Dig up and destroy the infected plants, including roots and stumps if possible. Do not recycle or compost the plant material.

The spread of honeyfungus may be inhibited by inserting a vertical barrier of heavy polythene or a pond liner (butyl rubber) in the ground to about 45cm (18 inches). The barrier should protrude above the ground 2-3cm (1 inch). This will hopefully prevent the spread of the rhizomorphs to other plants in the hedge.

Improving the growth of Leylandii by attention to soil drainage and nutrition, should render them less likely to succumb to honey fungus.


Phytophora is another soil-borne disease that can be introduced into the garden in various ways, such as on infected plants, in irrigation water or in soil or wind-blown dust. The fungus may be dormant in the soil for years and may only infect plants when the conditions are suitable. Whole plants will turn a grey/brown and then die.

Phytophora tends to infect plants that are under stress and especially on poorly drained soils. It can affect Leylandii when they are small but tends to have less effect on larger, established specimens. Many varieties of Lawson’s Cypress are more prone to Phytophora and should be grown on free-draining soils. Generally, once the foliage starts to turn brown, the infection is well advanced and the plant cannot be saved. Dig up the plant and remove as much of the soil, roots and stump as possible.

Aphids & Leylandii

Cypress aphid (greenfly) is occasionally found on Leylandii in late winter or early spring (January to April). It over-winters on Leylandii and can cause a problem especially on hedges that have been trimmed back very hard in the autumn or plants that are under stress for some other reason, e.g. plants where the soil is too dry or too wet. The damage is not apparent until the late spring when brown patches appear in the hedge, by this time the aphids have long gone and it is too late to treat the hedge.

Aphids & Leylandii

The colder winters of 2010 and 2011 will have reduced the number of aphids that have survived and significantly reduced the problem but it is worth checking your Leylandii hedge in January, February and March for large greeny/brown ‘greenfly’ on the young shoots. These are usually found 2 or 3 inches (5-8cm) within the hedge on the bark of the shoots. They are well camouflaged so can be difficult to spot as they are the same colour as the bark. They align themselves on the shoots in rows.

If the aphid is present, spray with an insecticide such as Scotts Bug Clear Ultra or Bayer Garden’s Ultimate Bug Killer. These are systemic insecticides that will kill the aphids on contact and remain in the plant to protect against new attacks for approximately six weeks.

Cut out the brown patches as they will not re-shoot. Encourage other green branches to grow back over the brown patches to cover them up.

Note: Brown patches can also be caused by trimming a Leylandii hedge too many times a year. A Leylandii hedge only needs trimming once a year. If it is trimmed more frequently, the hedge doesn’t have enough of a chance to re-grow and recover from each trimming and this weakens the hedge making it more susceptible to attack from other problems as well as Cypress Aphid. Trimming frequently also creates a lot of “thatch” or dead material that can act like a sponge holding water on the foliage. This can results in diseases like Botrytis and Pestalotiopsis which can also cause brown patches. If you brush or rake the hedge after trimming, it removes a lot of this “thatch” and improves the air flow around the foliage making it much less likely for problems to occur.

In summary:

  • Only trim your Leylandii hedge once a year.
  • Don’t cut your hedge back too hard, just to the same point each year, leaving 4 inches (10cm) of green growth on the hedge.
  • Trim your hedge in spring or summer, not late autumn.
  • Brush your hedge with your arm or rake your hedge after trimming to remove any “thatch” (dead material or trimmings)
  • Check your Leylandii hedge from January to March for Cypress Aphid, if it is present, spray with Scotts Bug Clear Ultra or Bayer Garden’s Ultimate Bug Killer.