Question
I live in zone 4 and have a couple areas on the shady, north side of my house where I have transplanted (approx. 2 yrs ago) various rhododendrons, hydrageas, and yews. The heavy clay is taking its tolls on these plants; Hydragea flowers not as bountiful; rhododendrons leaves getting brown spots in the summer; yews turning brown; All probably resulting from too much moisture.
The first step I have taken was installing gutters to minimize the water from the roofline that is directly above.
My next step is to dig out upper layer (6 inches)of clay and replace with some organic matter & sand that will eventually mix in with clay near plant roots.
Or should I dig out plants during early spring thaw and replace the top layer of entire area (12x8'). Hydrageas and rhododendrons are about 4' tall. Yews are 3 ft. spread.
What would you advise?
Thanks.

Answer
Hi TJ
Dig out your Shrubs and replant them with a mix of good topsoil and compost the holes should be twice the size as the  rootball. second  till in compost to the top layer of clay do not use any sand that just make the clay harder. then every year add about 1 to 2 inches of compost to the surface it will work its way in and in a few years you will have a workable area.  Good Luck  Larry  ;-)