Horticultural practices do change and research can be a driving force. It wasn't too long ago that standard practice to stake a new tree was a six foot T bar and and a strand of wire.
I am looking for answers that quote references from universities, professional journals or government agencies.
First, you have to find out Why people stake trees. What benefits are there to staking young trees? In nature, trees can germinate, grow, and mature without being staked. Here are some reasons why young trees are often staked:
If the tree has a floppy trunk that is not self-supporting, support staking will be needed. Colorado State University
These are legitimate reasons for staking trees, but there are some less beneficial side effects. These can include:
may be damaged by rubbing and girdling from stakes and ties
the trunk will grow and bend away from the stake
the trunk will be stressed more at the point of stake attachment and subject to increased breakage
provide more wind resistance because the top of the tree is not allowed to move as much.
develop weak wood from the staked position down towards the base of the tree; trunk movement is required for optimum strength of wood during development and growth.
produce less roots.
reduce stem taper which means less strength of the bole or trunk of the staked tree.
height growth may be increased.
Therefore, trees should only be staked if necessary, and only for the time period necessary.
As I mentioned before, some trees require permanent staking. In those cases, most of these side effects are non-issues, as they will not compromise the tree in future years, under the permanent staking conditions.
It is true that there are situations when a young tree is thankful for some mechanical aid, but not as often as many gardeners imagine. Furthermore, even when staking is beneficial to a newly planted tree, it usually remains so for only a short period of time. Fine Gardening
Not all trees should be staked. If they can support themselves well, and can handle the stress load from wind in your locality, the side effects of staking will do more harm than good. One must use good judgment when planting a tree, when deciding whether or not to stake. Additionally, if you decide staking will be beneficial, proper monitoring is required, to watch for girdling/damage to the bark, and for root establishment (once the roots get a foothold in the new environment, the staking is no longer helpful).
You want the staking job to support the tree, but not hold it tight. You will have much better development in the trunk if you allow some play. Two stakes is usually good for this, providing much more balanced support than a single stake, while allowing more play than triple. Using three is good only where necessary, to keep trees from rocking or working loose in heavy winds. Here is what I do:
Choose two strong stakes, hardwood or softwood, Pine or Hemlock will last longer. These stakes should be at least 6 feet tall, about 2 inches square and pointed on one end to easily penetrate the ground.
Determine the direction of the prevailing wind and insert the stakes exactly opposite one another, about 2 feet from the stem, in line with the wind. For example: if the wind direction is westerly, then place the stakes North & South.
Drive the stakes vertically at least 2 feet into the ground. Try to bury the stakes so they are the same height above ground. When finished, stakes should stand upright at about 4 feet. (I personally find that depth overkill in my location, 2 feet is about the maximum depth I put stakes)
Cut 2 pieces of flexible wire, each measuring at least 5 feet long. Also, cut up an old garden hose into 2 eighteen-inch lengths. Then, slip the hose over the wire, and wrap the hose around the tree to protect the trunk from the wire. Pull equal lengths of the wire parallel to the ground and attach to the top of the stake.
Twist the wires together on the outside of the stake to make the wire taut and nip off any excess.
You can do the same thing if 3 stakes are necessary, simply use 3 stakes instead of 2, spaced evenly around the tree.
About how long to leave them staked:
Short answer: As short a duration as possible. Ideally, stakes are a quick aid in the establishment of the tree, and have no part in long term support. From here:
Staking a tree that does not need it can do more harm than good. Movement of the trunk helps strengthen it by thickening it and giving it taper from bottom to top. Trunk movement also stimulates root growth. So although staked trees might grow taller faster than their unstaked counterparts, their trunks are weaker and their root systems are less developed.
When done incorrectly, staking further compounds a young tree’s problems. If a tree is tied to a stake too tightly, girdling can occur, weakening and even possibly killing the tree unless the problem is addressed in time. Movement of a tree above where it is tied too tightly to a stake, like movement of an unstaked trunk, results in a thicker trunk above the tie. This difference in thickness upsets smooth travel of water and nutrients up and down the developing trunk. Too tight a tie coupled with too rigid a stake can anchor a plant so firmly below the tie that a strong wind can actually blow off the top of the tree. Tying a tree too loosely to a stake also causes problems. The bark is continuously rubbed, resulting in wounds that may never heal properly.
It can take longer, though, if you have very hard soil, and the tree takes more than one year to anchor into it.
As mentioned before, some trees, like standardised shrubs and vines, and dwarf fruit trees, need permanent staking. From here:
A permanent stake is usually a thick treated wooden post, about 2m - 2.5m / 6ft - 8ft in height (or more), which is banged into the ground vertically beside the tree. (In fact usually the stake is planted before the tree). Permanent stakes can also be made of metal. In commercial orchards the stakes may be thinner but in turn supported on a strong wire trellis. In all cases the permanent stake forms a rigid inflexible support for the tree.
A permanent stake has a very different role to a temporary stake. Whereas a temporary stake is there to encourage the growing tree to thicken its stem and eventually become self-supporting, the permanent stake is designed to take-over most of the load-bearing role of the main stem of the tree. This means the tree puts less of its energy into growing a thick trunk to support itself, which means more energy for fruit production. The stake has to be permanent because if it is removed the tree will simply collapse.
Permanent stakes or some other permanent support are always needed for trees grafted on dwarf rootstocks, because these rootstocks are generally too small to support the tree in windy conditions.
Permanent stakes are a standard feature of most commercial orchards, and are particularly effective when the tree is trained with the central leader retained (and tied on to the stake). This form (often known as a spindle-bush) is very productive, and allows light to enter the tree which enhances fruit quality, as well as encouraging the tree to start fruiting much earlier in its life. The benefits of the permanent stake and the central-leader tree forms are equally applicable to the garden situation, especially for apple trees and pear trees.
The stake must be strong (with the ability to support hundreds of pounds of fruit), and long lasting. Galvanised steel is a good alternative for treated wood, so you can avoid chemical contamination of the soil around your fruit tree.
If the stake goes down, your dwarf fruit tree goes with it
Permanent staking ensures a weak trunk. That's why it's so imperative for a permanent stake to be able to handle the workload. Make it overkill.
Another viable method to support these trees is trellising
About standardised ornamental shrubs and vines, you want them to support as much weight as possible on their own, even though they are not capable of handling their entire weight. Be minimalistic. One rod, like 1/2" rebar, pounded into the ground right by the trunk and attached via elastic bands, is good enough for small ones.
With a bigger tree (over 3" diameter), you need something heavier.
https://www.extension.iastate.edu/forestry/tree_planting/stake.html
http://www.forestry.gov.uk/pdf/eng-treecare-guide.pdf/$FILE/eng-treecare-guide.pdf
http://www.orangepippintrees.co.uk/articles/staking-fruit-trees
http://extension.psu.edu/plants/gardening/fphg/pome/pruning/pruning-and-training-to-a-trellis
http://ag.arizona.edu/yavapai/anr/hort/mastergardener/mgcourseresources/az1402.pdf
http://www.myminnesotawoods.umn.edu/2008/12/staking-and-guying-trees-best-materials-and-technique/
http://www.umass.edu/urbantree/factsheets/10stakingtrees.html
http://forestry.about.com/od/treeandforestcare/i/tree_staking.htm
http://www.rootmaker.com/sites/default/files/pdf/staking.pdf
http://umaine.edu/fruit/growing-fruit-trees-in-maine/rootstocks-and-dwarf-fruit-trees/
I'll just throw this in for interest's sake - I tend to follow the Royal Horticultural Society's revised (about 10 years ago) recommended method, and conveniently, there is a picture in this link below showing the angled, short stake. I use this for trees that will not require permanent staking
