Plants Per Metre In A Single Row Hedge

Spacing a Single Row Hedge at 3 Plants per Metre

• The most common spacing for a garden hedge is at 33cm: that's 3 plants per metre in a single row.
• When mature, a human will not be able to squeeze through it.
• Country hedges that need to be stockproof (i.e. to block horses and cows) and/or qualify for a Countryside Stewardship Grant should be planted at 6 plants per metre in a double row.

In the bird's eye diagram below of a two-metre hedge, the grid represents the minimum possible footprint of the hedge: the mature width will be down to how you clip it, and 33cm would be very narrow for most hedges, but it will do for this example, where we are concerned with the spacing along the length. 

Correct Single Row Hedge Spacing at 3 per Metre 

The black dots represent a hedge plant, and the red line marks the end of the first metre.

Note is that you (typically) do not put your first & last hedge plant on the 0cm and 100cm mark of each metre that you want covered by your hedge. 
Instead, you put your first plant about 16.5cm (at least) into the first metre, and the third plant will be 16.5cm from the end, and they will grow out to fill the whole metre footprint.

The diagram below shows what it looks when 3 plants per metre is done incorrectly, with plants on the 0cm and 100cm marks, which leaves you no choice but to space them 50cm apart.

Also, to complete the next metre, you would only need two plants.

Incorrect Single Row Hedge Spacing at 3 per Metre

The diagram below shows 3 plants per metre done incorrectly, with plants on the 0cm and 100cm marks, so you have to space them 50cm apart.

Also, to complete the next metre, you would only need two plants.

There is nothing wrong with spacing hedge plants at 50cm: this is a common spacing for ornamental hedges that serve no security purpose, and thorny hedge plants would still certainly knit together into a secure hedge.

The same principle applies to a 50cm spacing as a 33cm spacing: you don't put the first and last plant on the 0cm and 100cm marks, but on the 25cm and 75cm marks.

Correct Single Row Hedge Spacing at 2 per Metre