Hi, this is Kimberly here from landscape-solutions-for-you. Thank you for taking the time to post a question on this website.
There are a couple of things you can do since you have pruned back your Yews. You can loosen the dirt and add some organic mushroom compost to the soil. This is an organic fertilizer that will last up to one year. It doesn't smell great, but your Yews will love it.
You can also add some good quality fertilizer that has phosophate and calicum in it. 10 - 10 -10 is a good choice. Make sure you get on a good watering schedule since you have pruned back, as this will help with new growth. I just put up a page today on the Yew family so go ahead and feel free to check it out, on the for you blog.
Thanks again and feel free to ask questions anytime. Share your Yew pictures if you would like. Have a great day!