I have just planted 6 leylandii at approx. 3 ft apart. They were 6 ft tall when I bought them last month. I want to grow them to about 15 ft and want them to merge together with a nice thick healthy growth.

Can you suggest when I should trim, and do I need to control the height growth at the same time to allow the width to establish?

  • what part of the world are you in? Were the plants in pots or bare root?
    – Bamboo
    Apr 25, 2020 at 14:37
  • They were in hessian sacks I believe, which I planted them with, which I also hope was the right thing to do. London, UK.
    – Graeme
    Apr 25, 2020 at 14:58
  • You do know there is a law relating to high hedges (over 6.5 feet tall)? Your neighbours can apply to the council for an order to have them cut back if they affect the ‘reasonable’ enjoyment of the neighbour's house or garden. Apr 26, 2020 at 15:40

1 Answer 1


The advice is to leave hessian in place when planting (though I personally never do unless the roots have already penetrated the hessian). You now need to go out and reduce the height of the plants by half - I know it sounds like a lot, but it is necessary to encourage shoots from the base to make a thick, dense hedge down to the ground. Do not prune again this year, but next year you will need to clip or trim over fairly lightly at least 4 times, including the tops of the plants. When clipping over, bear in mind the base of the plants should be left a little wider than the tops. Keep doing this until the hedge has reached the height you desire, then after that, its a case of pruning back 3-4 times a year to maintain the shape and keep the height down.

Given the weather we've been having,the ground is currently very dry - keep your plants well watered for the rest of the spring and summer, right up to November. You may need to take care of watering during next spring and summer too if it's dry and warm - after that, they should cope without being regularly watered.

  • OK, thanks for the advice, sounds harsh but I will go do it tomorrow. Do they grow continually throughout the year or are there certain times they grow and other times they stop, i.e. during winter?? Thanks again
    – Graeme
    Apr 25, 2020 at 15:17
  • They might stop in winter if its very cold, but if its like last winter, they'd probably grow a bit. They are fast growers, these trees - you should probably aim next year to clip back in March or early April (depending on the previous winter) again mid to end of May, again June/July and again September/October.
    – Bamboo
    Apr 25, 2020 at 16:40
  • Thanks so much.
    – Graeme
    Apr 25, 2020 at 16:49

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