My Pfitzer juniper is about 30 yrs old. It is very large and lives by my back fence. The front is healthy but the back part by the fence has died. I would like to know if I can cut it back to one foot above the ground and have it grow back.
Now is not a good time for pruning. At this time of the year when the weather is starting to get colder trees and shrubs are starting to get ready for winter by slowing down their respiration and production systems. It goes into dormancy. When a plant is pruned at this time the plant will turn it’s attention to replacing it lost limbs through growth and will not be ready for the cold temperatures and may die.
A good time to prune is in the winter or early spring when the tree/shrub is still dormant and growth has not started. At this time the sap is not running and with deciduous trees the shape of the tree is easier to see. For your juniper you may want to wait a bit and see if there is any new growth in the sparse areas before you start pruning.
All junipers have a dead zone in the middle due to insufficient light. This may be the problem with the part of your juniper that is against the fence. This area will not grow back unless you see some green growth in there.
For any juniper severe pruning is not recommended. It is suggested by the Morton Arboretum in Illinois that you should not cut down a juniper by more than 20 percent. What you could try is reducing your shrub by 20 percent each year but remember that the dead zone might be truly dead and that will not grow back. This may also over stress the shrub and cause it to die at some point.
I guess it all depends on how much this shrub bothers you. If you do cut it down to the ground it will not grow back but that will give you room to plant a new shrub that is more compatible to your garden in terms of size. There are a lot of dwarf varieties available now, not like 30 years ago when the selection was small.
The following article provides additional information on pruning of evergreens: https://www.mortonarb.org/trees-plants/tree-and-plant-advice/horticulture-care/pruning-evergreens