In general, the spacing of a hedge plant is based on its mature spread but that can be fudged a bit depending on how dense you wish the hedge to be and how fast the coverage. 6-8' is the recommended spacing for Pacific wax myrtles......the smaller number offering a slightly denser hedge sooner. One could take it somewhat tighter but you risk some interior dieback and loss of foliage due to excessive shading by the neighboring plants

Once established, growth is pretty rapid so at the above spacing, I'd expect decent coverage in about 3 seasons. Pruning back the leading shoots once or twice a season will result in somewhat denser lateral branching as well -- a shorter but bushier plant.

We planted a 100' PMW hedge in the fall of '08 placing the shrubs about 8' apart on average. Today there still are 4'to 5' gaps between them. The stems have matured noticeably but the shrubs height and spread are only marginally larger now. They have been nibbled on by deer during that time as well. I hope to see some acceleration in their growth now.

Not a follow-up, this is a fresh question. Last spring I planted 6 PWMs on a steep, south-facing slope in Corvallis. All were planted equally well and are on drippers. The deer nibble on them a bit. By last fall it was evident that only two are thriving, with a foot of growth, nice dark green color. The other 4 are pale green and have grown only a little. I'd sure appreciate some advice. Thanks, Tony.