mike wrote:
I'm thinking of planting a hedge row of Green Giant Arborvitae. �I
want to plant them tight (3 foot on center), because I don't like the
V-shaped gaps I've seen on other Green Giant hedge rows planted to the
"recommended" spacing.

My other plan is to keep them sheared to a rectangular envelope 4-6
feet deep and 12-20 feet high.

Does anyone see any problems with either of these plans?

Sounds like you're very anxious to block out a neighbor.

Just how are you planning to keep a 20' tall, 6' wide hedge sheared?
If you plant typical 2'-3' tall nursery stock now and lets say you're
30-40
years old, by the time your plants reach 20' tall you may be a sixty
year old man who will very likely be incapable of maintaining that
hedge. Why pray tell do you want a 20' hedge, if for a wind break
then you don't want all the same plants, at least not those that
require shearing.

You don't mention the growing zone where you're located and how long a
hedge. Personally I would never consider a hedge of arborvitae. they
don't have a very long life span so if a few die prematurely you end
up with a very unsightly hedge.... arborvitae are best used as single
specimen plantings, or planted spaced out along a path or driveway to
deliniate, or perhaps just two or three in a grouping so if one or two
don't make it and need removal no one will notice a gap. And 3' apart
is much too close (that gives only 18" of space per each side, you may
as well erect a stockade fence). You'd do much better to plant two
rows, staggered, and like 6'-8' on center. I think Canadian hemlock
makes a much nicer hedge. But whatever you choose you need to have
patience for the plants to approach a mature size, cramping them
closly together in an attempt to create a hedge prematurely will
become a disaster, you will have wasted your effort, your money, and
mostly a lot of years before you're faced with a do over.