1. How many plants do I need for my hedge?
For most garden hedges, multiply the length of the hedge in metres by 5 to calculate the number of plants required. This corresponds to a spacing of 20cm (8 inches).
If it is to be a low hedge, say less than about 40cm high, then length in metres times 6 (16cm/6.5 inches spacing) is better. For tall hedges, over about 80cm high, length in metres x 4 (25cm, 10 inch spacing) is generally enough.
4. How fast does box grow?
Once the plant is established, buxus sempervirens will grow about 6-9 inches a year under reasonable growing conditions. In deep shade, very poor soil and very exposed sites, the growth rate is lower.
Most of the named varieties of buxus sempervirens, and the other species of buxus grow rather more slowly than buxus sempervirens.