Time of year:
Any time of year works, as long as the ground is not frozen, or the air very hot and dry. Obviously frozen ground will be 'hard to work with', and you will not be able to plant the tree properly. If the air is hot and dry, then sometimes even when the soil has sufficient moisture, the tree with it's compromised root system could dry out and lose top growth.
Whatever is appropriate for the particular species. Remember this is a large root ball, and to plant it properly, you cannot have obstructions such as jutting rocks. You should never remove part of a root ball while planting these.
The hole should be ready as soon as possible after the tree is dug out, for the least stress on the tree.
- Remove the sod, if the tree is being planted in the lawn. I use a flat spade and then roll the sod up and place it to the side. If planting in a mulched landscaped bed, pull away the mulch to the diameter of your hole.
- Remove the soil.
- I place tarps adjacent the hole, to ease the cleanup afterwards.
- I separate the topsoil by throwing it in its own pile.
- The sides should be steep, and the diameter should be bigger than the root ball (at least a spades width the entire way round, for easier work.
- The bottom should be flat. If the ground is very hard, I dig six inches too deep, and then place the soil back, sometimes with a bit of organic matter.
- If the hole is made far in advance, covering it can help keep the soil soft.
Prepping the tree:
Make sure the root ball does not dry out. It's very stressful on a tree right after a large percentage of the roots are cut. For planting, you want tacky soil that sticks together, so that less densely rooted regions of the root ball don't collapse.
On conifers, I sometimes take a rope, tie it to the base, and then wrap the tree up (sort of like how people contain Christmas trees with netting., so that I can easily work around the tree, especially once it's in the ground.
Planting the tree:
Assuming the hole is finished and appropriately dug, the root ball can be placed in the hole. If the tree is tall, and contained with twine, you can remove the upper portion of the twine before standing the tree up, so it's easier to reach. If you are strong enough to lift the ball into the hole, or are capable to do it with help, that is preferable. alternately, gently roll the ball into the hole, trying not to crack it or otherwise lower the strength integrity. I've planted trees that were grown in pure sand, and keeping the root ball whole is not possible. Just do the best you can. Try to roll it into the hole, rather than sliding it, so you don't cave in one of the sides of the hole.
More important for specimen than mass plantings: rotate the tree so that the fullest, most aesthetically pleasing side is facing the direction where it will be most often viewed (ie a certain porch or window, or the road). If the root ball is solid and small enough to easily lift, you can remove the burlap wrapping here.
Backfill. (always re-check that the planting depth is right. 2 inches high is fine. Low is not fine. Also be aware of where the root flare is - sometimes there was soil on top of the flare when the tree was dug, and will make the root crown lower than is healthy when you clean it off)
- I begin by taking a spade, and cutting in the edges of the hole, all the way around. Especially in clay soil, breaking the sides can prevent roots circling the hole (common in hard clays). The soil you break loose will fall into the bottom of the hole.
- Tamp the loose soil at the bottom of the hole, holding the tree very straight. You can use a small tamper, your boot, or the top of a sledge hammer all things I've used). This will balance the tree so it doesn't keep moving around in the hole.
- If you didn't do it by this point, it's time to remove as much burlap as possible. If there is a wire basket on the ball, cut it away to the point that you tamped, so that a) you can remove the burlap down to that point and b) so that the wire does not girdle the tree when it grows large (only in large growing trees) Cut the twine that ties the burlap, and cut it off as low as you can, while not moving the root ball. The burlap can be discarded.
- Begin throwing soil into the hole. break up large clumps, and remove large rocks (hand sized or bigger). You can throw in soil additives (especially organic matter) at this point. Do this carefully, as you don't want to change the soil type. if you change the soil type far from the soil outside the hole, it could begin acting as a sponge and hurt the tree (especially when planting in clay).
- When the hole is full, tamp in again. Make sure there are no air pockets. Even if you have clay, you want to have it well tamped.
- Do the final fill (this should be topsoil, if you separated that). do not add soil on top of the root ball.
- Do the final tamp - just enough to settle the soil and remove air pockets - you don't want this layer to be impervious to water.
Look at the base of the tree, where the trunk meets the ground. You should be able to see the root flare easily. If not, pull away soil until the top of the root flare is uncovered, and level the top of the soil.
Directly after planting:
Trim any broken or crossed branches, and make sure the branches are naturally extended (they can get cramped, and caught on each other, etc, between the time the tree was dug, and replanted). If there were tags on the plant, remove those.
Any time the tree is actively growing, or if the soil is dry (crumbly or powdery), the tree should be watered. Don't let the root ball dry out, but also focus on the edge of the planting hole, where the new roots will be pushing out.
If the ground is frozen, do not water. If you are having a cold, wet, winter, even if the soil thaws out, supplemental water is not necessary until the soil begins to dry in the spring.
In climates where the tree can grow without waterings once established, keep it watered for the first growing season. the next growing season, only water if the plant is showing stress from low moisture (such as leaves withering or dropping prematurely). After that, it should be established.
An organic mulch is extremely worthwhile, and conserves moisture while eliminating weeds and adding organic matter to the soil. It can also help somewhat with frost heave in colder climates. 3 inches deep or so should be plenty, and if you can go out to the tree's dripline, that would be ideal. Remember to keep it off the trunk and the visible root flare (further reading).
Staking should be avoided at all costs. A root ball from a balled and burlap transplant is heavy, and should be sufficient in keeping the tree steady, if planted properly. I once had the experience of planting a small redbud with an oversized dry clay rootball, which was cracked directly from the root flare down the center. Even after the best planting job I could manage, the tree still opened the root ball crack badly when blown by wind. I staked it for 1 season, and it was fine. See my thoughts on staking here.
Don't fertilize while planting, at least not with chemicals, or you can do damage to the roots. Once the tree is growing, you can begin fertilizations if desired, according to the needs of the plant/soil.