I have a 30 foot high Yew tree with a broad canopy about 40 feet across.
Seven years ago I planted a Trachelospernum Jasmonides each side of the Yew10 feet away from the trunk when the canopy was about 20 feet wide.
Both plants have grown very well against the fence (which is south facing) just behind the Yew. However the amount of blossom has diminished over the years, though I suspect that this could be because of less sunlight as the canopy has grown and shaded them.
I also planted some Lily of the Valley close to the trunk of the Yew and they have prospered well and spread happily.
However, as Jasmonides is a thirsty plant I make sure that I water it heavily and regularly throughout the year. Without this, the dry conditions underneath the Yew canopy woulkd have killed them off years ago.
The grass that was growing around the Yew has retreated as the canopy has expanded. Not much I can do about that one.
I am drastically reducing the width of the canopy to let more sunlight onto the Jasmonides in the hope of reversing the decline in blossom.
One of the great things about Yews is that you can be really brutal with pruning and lopping. They recover with considerable vigour, and after a second season, you really cannot notice what was chopped back.