I do light, yearly pruning in mid July on yews. Their annual growth is done by then, they are semi dormant, and they have time to harden off before winter. If I'm going to do heavy pruning, I do it in March.

tj

tsugajunkie, Thank you!
Could you tell me how I should accomplish making them narrow and or how to trim? Can I do any harm?

Not likely to do harm as yews are very forgiving. They have dormant buds everywhere. For a detailed approach to the pruning we'd really need a pic and an idea of the look you're after. Generally speaking, a trimmer will leave a more formal sheared look and cutting back individual branches to a fork or larger branch would be more natural. Which method you use not only depends on the look you want but how many plants there are and how much time you want to spend.

tj

a pic of your plants.. will get you more precise answers ... though the junkie covered the basics ...

ken