If in doubt, don't. Otherwise yews can be cut anywhere between the root crown and the branch tips and will grow back. Optimal time to prune them is late spring-early summer.

Is this double post? I thought I had posted with the suggestion of opening up the lower parts, exposing the beautiful bark and making it look like a small tree. I have seen this and it's very attractive. I've also done it though not on my property. It was quite striking.

its a conifer ... which is also a tree ..

in our rather short growing season.. say compared to the near year around growth of the PNW ... if you cut this thing down significantly ... you will spend a decade watching it try to recover to any semblance of looking good ...

and if that is true.. you have to ask yourself.. do i want the whole world to watch this nightmare project on the corner of my castle.. as all the neighbors walk down the street pointing and laughing at your house ...

cut it to about 3 feet.. sharpen a shovel.. and start digging ... and get rid of it..

if you can sacrifice planting on that EXACT spot.. cut it flush to the ground.. and it will be dead... or.. just to be sure.. apply some stump killer...

i bet that sucker was planted the summer after the house was built.. it might be magnificent on a golf course fairway.. to bad its isnt where it is...

now all that said.. if you want to practice pruning.. like you dont get enough of that out back.. lol.. go for it ... whats the worse you can do.. piss yourself off so bad.. you get rid of it.. well.. see above.. that is highly approved ... if not encouraged ....

ken

ps: i doubt much of anything will live planted under it ... its hard to establish new perennials or annual in soil that has 50 years worth of tree roots.. and if you do any significant soil digging.. you are going to screw up the conifer ... or have to water so much.. the yew doesnt approve ...

I limbed up a large yew like yours into a tree shape at our old house and it looked wonderful. However, you do have to keep pruning it on a regular basis - yews will sprout new growth everywhere. If you're not fond of upkeep, then cutting it down and planting something smaller nearby would make sense.

You can't let yews grow a lot and then expect to trim then down. They have to be constantly trimmed. You can cut off lower branches and try to make it look like a tree. if it looks bad, then get rid of it. Digging up the stump may be impossible without a back hoe. If you cut it way back, expecting to regrow, it might just die instead. It's happened to me.

I have found that removing overgrown yews to be a major improvement. I don't remember ever regretting cutting one down but several times I have returned to cut down more after getting started. 

If you aren't sure, you could cut it down to manageable size next March and then finish the job in the fall if you don't like the result. I figure if the yew dies after getting cut to appropriate size, then it had to be taken out anyway.