Thuja planting and pruning

I have just planted about 20 6ft Thujas to form a new (and instant) hedge. I have read a general remark that one is supposed to trim a large amount off the top on first planting to encourage growth at the side but cannot find anything specific. Can anyone provide advice please.

 

Not appropriate for Conifers, like Thuja, IMHO. They need a single, strong, leader.

Let them grow up to about a foot taller than final height, then cut them to 6" below final height (so the tops then bush up a bit), and then cut at final height once they have regrown a bit.

Start clipping the sides gently as they approach the desired width - each plant grows outwards in a circle, so there will be a part of that circle which reaches the desired width before the rest of the plant, so lightly trim that a bit before it gets to the desired width, and then as the whole plant bulks up, and fills the gap to its neighbour, let it grow outwards to the final width. You can do it by eye until they have bulked up enough to then need a line to make a nice straight cut along the face

As you train/trim the face of the hedge give it a "batter" (narrower at the top)

Planting 6ft hedge plants will need serious staking. Either individually (as you would a tree) or a substantial post periodically along its length with horizontal wires that the individuals can be tied to. Make sure the wires don't make direct contact with the bark of the plants such that they "rub" in the wind.

The plants will need plenty of water in their first year; more so because they are semi-mature (and even more so if they have been provided bare-rooted rather than container-grown). Personally I would install leaky-hose along their length, making sure it was close to the stem at the base of each plant, so that I could water them thoroughly once a week (hose probably needs to be on for an hour), twice a week in very dry weather. Heavily watering each time is more important than often. Whatever you do please do not water "Little and often", that will kill them." Watch out in case the far end of the leaky hose delivers much less water than the near end - put some bowls along the length of the leaky hose and see how much water is collected. If it is much less at the far end then perhaps better to connect the hose to the middle of the leaky-hose with a Tee connector so water has only 2 x half-length sections to pressurise.

I would also put some weed suppressing membrane along the run, at least 1M wide. Perhaps best would be two strips of 1M either side, with slits cut to accommodate each plant, and the two strips overlapping in the middle by about 25cm. This will keep the weeds down and the moisture in (put the leaky hose under the weed suppressing membrane). Allowing weeds to grow will seriously steal moisture and nutrients from the newly planted hedge. Dig a slit along the front edge with a spade, tuck and inch or two of the edge of the weed suppressing membrane into the slit and then stamp it in - much cheaper, and better IMHO, than using "pegs" (which are blinking expensive!)