The amount of site preparation necessary will depend on the previous site use. This will also heavily influence the methods needed.
On former agricultural land, you may only need to carry out relatively basic preparation, such a spot spraying to remove weed competition, while on sites that have been clear felled, more significant work may be necessary. The Forestry Commission has produced an information note on Forest Ground Preparation (Information Note ODW 10.01) with examples of best practice and indicative costs (though it was written in 2002 and the relative costs will have changed since then).
When to plant
Planting should be carried out when the tree is dormant. This means that there are no fixed dates that define exactly when it is appropriate to plant, the “Planting Season” usually lasts from around mid November to early March, but this will depend entirely on the site and weather conditions. Most native broadleaf species are entirely dormant after they have shed their leaves until spring, while conifer species are usually dormant if the average day temperature is lower than about 5 degrees.
All trees are vulnerable to root damage while they are being planted, but bare rooted tree stock is particularly susceptible. The critical factors are dryness, and frost damage. Don’t plant in snowy or hard frost conditions and make sure that all trees have the roots covered at all times by a plastic bag to prevent drying.
Depth and soil
You should be planting trees at the same depth that they were growing at in the nursery. The easiest way to do this is to make sure that the “collar”, where the roots meet the main stem, is at ground level. If you are planting into clay soil, make sure that the spade has not left a smooth unbroken face on the side of the hole as this will restrict root development. Once the tree is in the ground make sure that the soil is properly pressed in around the root system, to prevent air pockets. There is a more detailed set of notes available from the Forestry Commission: (Tree Planting Information Note ODW 10.02).
There are a number of different things you can do to help newly planted trees to establish well and grow quickly. These measures are largely to decrease competition from other plant species, and deterrence of pest species.
Spiral guards are an effective deterrent to rodents and small mammals such as rabbits
Tube shelters can also prevent grazing by small mammals, and provide some protection against weed competition. They also increase the temperature of the microclimate, leading to faster growth. They are nominally photo-degradable, meaning that they shouldn’t need removing when the tree gets too big (there is a lot of anecdotal evidence to suggest that this is far from trouble free, and they may need removing when the trees out-grow them.)
Stock fencing prevents grazing by domestic livestock, and can be upgraded to prevent deer grazing on the young trees. A layer of small diameter mesh at the base makes the fence effective against rabbits.
Spot spraying of is an effective way of removing competing weed species and allowing the trees to capture the site.
Stakes are usually unnecessary on small whips or plug grown trees, but may be useful for stabilising standards. Make sure that you fasten the stake no higher than a third of the height of the tree as to allow the crown to move in the wind. This stimulates root development and will lead to a healthier tree.
Mulch mats are an alternative to spraying on smaller sites, they are also helpful on sites where poor moisture retention is an issue.