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.
It's easy to hurt your back when moving a heavy tree.
Avoid the use of make-shift planks for ramps than can slip out. The weight of a heavy root ball can crush a person, causing very serious injuries!
Branches often poke you, so wear eye protection.
Pinning nails are used by nurserymen to hold burlap on the root ball -- the points are extremely sharp and will snag you if you aren't careful.
Tree placement should take into consideration a tree's growing requirements, maximum size, easements, right-of-ways, and property lines.
Right-of-ways may extend 15 feet or more into your lawn area from the street. Consider that someday sidewalks might be added to that area.
Laws may allow neighbors to trim off branches reaching over the property line. Check your local laws and ordinances, and even if you are allowed to trim off a neighbor's tree branches, try to discuss the issue with them first in order to maintain a good neighborly relationship.
If you plant a tree over a utility line that may need to be dug up later, it could mean the tree will have to be cut down.
How is the soil drainage? Most plants don't like soggy soil.
Use trees to block ugly views, but don't block the desirable views.
Deciduous trees only screen during the growing season, while evergreens will provide screening all year.
If you plant deciduous trees on the south or west side of your house, it will help cool your house in summer while allowing winter sunlight through to warm your house.
Hedges of trees will act as windbreaks against cold winter northwesterly winds.
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.
Don't excavate any deeper than the root ball. B&B trees need a solid footing to sit on. Loose soil under the ball will allow soil to settle later, causing the tree to become tilted as it sinks.
Planting holes should be twice as wide as the root ball if feasible. When planting in poorly drained heavy clay, excavate a narrow ditch out of the lowest hole edge. Fill that ditch with loose soil that will allow water drainage. If the surrounding ground isn't sloped, plant the tree with the root ball elevated one-third of its height above the existing soil, and slope-up the backfill around the elevated root ball.
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:
Backfill with topsoil?
University research indicates that trees will establish better if planting holes are backfilled with the native soil. Improving the backfill (using peat moss, topsoil, etc) may cause roots to stay within the planting hole, due to differences in the types of soil.
Early recommendations called for thinning a tree after transplanting to compensate for the loss of roots during transplanting. More recent studies indicate you should only remove crossing branches or damaged limbs. That being said, many nurserymen still believe in thinning a newly transplanted tree to balance the 'root to shoot' ratio.
Stake the tree?
Trees over 6-feet tall should be staked for the first growing season. In windy situations you may need to stake shorter trees as well, with the principle being that a tree ends up straight once it roots into the ground. Recommendations also call for staking a tree so it can move slightly, the theory being it will develop a stronger root system with some movement in the wind. Protect the tree bark from wires and ties with short sections of old garden hose, which work well.
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.