I have a situation with leyland cypress growing as a privacy screen in poor heavy clay/rock soil on a raised ledge overlooking a home set about 10' below. They are planted at the edge of a forest but get a good deal of sunlight through the day and are never in deep shade. Their growth has been very slow due to both several years of drought and the extremely tough soil they're planted in. The trees planted where the soil was fill dirt from the home's construction are up to 30' tall, but the trees where they were just planted in the hard stuff with the usual 3x/rootball width hole they're maybe 6' tall after about 5 years! So I'm pretty sure it's the soil. Color is fine, health seems ok, they're just stunted. My question is, would drilling a series of 2" holes about 2 feet deep around the perimeter of the trees to break up the dense soil and get more water/etc to the root zone help them grow? Or is there another technique used other than ripping em up and bringing in some heavy artillery to dig a trench to put them in? I could even fill the holes with river sand if that would help. About 1/3 are growing normally, but the middle ones planted in really tough soil are just too short to serve their purpose as a privacy screen.