Larger landscape sized trees are usually balled and burlapped, or "B&B" as they are referred to in the landscaping business. Due to the weight of soil root balls (soil averages 100 lbs per cubic foot) moving and planting a large balled tree can be a daunting task usually best to professionals with experience and equipment.
The simple answer is: Transplant tress when they are DORMANT. But let's elaborate on that answer a little bit.
Trees with leaves that fall off in the winter are best transplanted when they have no leaves on them, which translates into late fall and early spring. However, some trees (see list below) are best transplanted only in the spring of the year.
GENUS OF DECIDUOUS TREE - COMMON NAME
Betula - Birch
Cercis - Redbud
Cornus - Dogwood
Craetegus - Hawthorn
Liriodendron - Tulip Tree
Liquidambar - Sweetgum
Magnolia - Magnolia
Oxydendron - Sourgum
Platanus - Sycamore
Populus - Poplar
Prunus - Plum
Pyrus - Pear
Quercus - Oak
Salix - Willow
Zelkova - Zelkova
Evergreens are quite similar when it comes to the best time to transplant them. Basically, when they are not actively growing.
One difference between evergreens and their leafy brothers and sisters is that evergreens can be transplanted earlier in the fall, once their new growth has 'hardened off" (September in the midwestern and northeastern US).
So that should answer the "when is the best time to transplant a tree" question.
WORST TIME TO TRANSPLANT A TREE
Let's look at the reverse of that question as well... "When is the worst time to transplant trees?" The answer is late spring and early summer as trees are growing and putting on their tender new foliage. In other words, when they are not dormant and actively growing.
BOTTOM LINE: Transplanting trees at the right time of year greatly improves your chance of success!
Burlapped trees should be moved by lifting the root ball instead of pulling on the trunk - it's easy to damage the small feeder roots on a balled plant.
If you are transporting a tree with leaves on it, wrap the branches with burlap or a mesh tarp to protect it from the drying effects of the wind. Try to drive slowly to minimize windburn.
Tree placement should take into consideration a tree's growing requirements, maximum size, easements, right-of-ways, and property lines.
THE FINE PRINT
Check before you dig for buried utility lines, wires and underground hazards by calling 811 known as "One Call" which is a free service for homeowners to mark underground utilities. Call a couple weeks ahead to allow time for the various utilities to mark the area. Landscape lighting, lamp post wires and electric dog fence wires are often shallow and very easy to damage, but you will have to locate those on your own.
Some research on tree planting suggests using methods you might not imagine. Did you know some research indicates it is better to backfill your planting hole with the native soil, instead of bringing in topsoil?
Research has indicated that tree roots will establish better if the soil they are growing into is the same. In some cases however, you are forced to dispose of heavy clay or rocks and use better soil for your backfill.
Having good drainage is probably the most important factor of all --- tree roots need to breathe and won't tolerate soggy soil conditions that can suffocate roots. Some species of trees will tolerate wet conditions better than others.
As mentioned above, recent university research overturned some old concepts about transplanting trees. Two of the most notable concepts deal with pruning and soil backfill:
2 stake method
Another method uses 3 short stakes spaced evenly around the base of the tree with guy wires running up around the first branch. Use sections of old garden hose to protect the tree from wires and rope. Purchase a tree watering bag
TREE TRUNK WRAP
Bark on a young tree should be protected with tree wrap, or a plastic spiral wrap, during its first year of growth. Place these wraps around the trunk of the tree, between the first set of branches and the ground.
Don't choke your new tree!
When placing any sort of bindings around a tree trunk, it's very important to check them from time to time to ensure they aren't choking the tree trunk as its trunk diameter expands!
We've seen many cases where these wires, plastic ropes, and synthetic wraps have caused the death of a tree. These situations most often occur in commercial landscapes where no one is paying any attention to tree maintenance after the initial planting work.