When should I top these Leylandiis to be the same height as the rest?

Had some trees burnt down by an arsonist. Planted a few more to fill the gaps. They’ve now just passed the height of the hedge. I have another gap where the new trees are much taller than these.

I wondered at what point I should cut the top to make them the same height? The trunks are very thin at the top so thought maybe I leave them grow a while to thicken up then cut? Because the other trees must have been topped at a taller height as their trunks are much thicker.

 

Hi voobmn not sure but a tree surgeon once told me improper pruning can cause lasting damage, or may even shorten the tree’s life also . pruning in late autumn or winter is best, when the tree is dormant. But to remove weak, dead or diseased branches and limbs, this can be done at any time of the year without much consequence to the tree

 

Hi Voobwm

I recommend trimming the tops as soon as possible, even if you're only removing a few centimetres of growth. The reason for this is that it should help promote thickening of the tree, it's less damaging to the tree, and it's easier to trim little and often rather than doing a big hit. The result will be a lot neater in the end. Keep on top of the trimming and don't let it get too big to trim.