Question
I have several arborvita in front of my house that do not seeming to be filling out.

I live in north Ohio and the soil is largley clay.  it also seems to hold more water in the  shurb area.

Should I fertilize them a lot.   The area gets sun about half the day.  They are getting a bit taller but not bushy.  Can you suggest anything?  Thanks

Answer
John,
Your Arborvitae are not thriving due to several conditions.
The first is the limited amount of sunlight they are recieving. Arbs thrive in full sun, the less light they recieve, the thinner they will become.
The second is the soil. Arborvitae prefer moist, well drained soils, not clay soils.
There are ways to help these shrubs to fill out. Fertilization in the spring is one thing that you can do.
If there is any way to allow more light into the area (ie. pruning trees back or a general thinning) that would also help.
The best way to help these plants is to start reconditioning the soil in the area. Use a bulb planter that will fit onto an electric drill and dig 6 to 8 holes in the root zone and just outside the dripline of the plants. Back fill these holes with a high quality topsoil that has a high organic content. The topsoil will create a better rooting zone and will help to improve drainage and as it is moved into the surrounding soil, it will mix with the clay, reconditioning it.
Limit the water in the area for a year and monitor it closely.
I hope that this helps.
Ed Gulliksen