Posted: 02/11/2015 at 23:19
I don't like the idea of planting such large yew trees as they tend not to establish as well as smaller plants, as well as being far more expensive.
As for spacing, at least two foot apart, so the individual plants have room to grow without competing. ( Christopher Lloyd's father wrote a guide to yew hedges and recommended planting two foot apart and then as the hedge grew to remove alternate plants to leave four foot spacings. ) Smaller plants, 18 to 24 inches high will establish well and reach a six foot in about 4-5 years.
If you type ' how to plant a yew hedge' in the search box above, you can watch a video by Monty Don on the subject.