western-queensland-gardening-guide.pdf - South West NRM

The tree's growing space extends around the plant, both above and below the
ground, and increases as the tree grows bigger. Anything that reduces this space
reduces the tree's growth. The competition from weeds above the ground is easy to
see, but it is in competing for water and nutrients below the ground that they are
most damaging. Eventually the tree reaches a stage where its size, both above and
below the ground, gives it an advantage over smaller plants-its larger leaf area
increases the tree's ability to manufacture growth materials, and its larger root
system explores more ground.
Although the small plants can now offer the tree little competition, nearby trees of
equal or greater size may limit the tree's light by shading it, or compete with its
lower roots for water. These trees in their turn now become weeds. Eventually,
though, the tree becomes so large that it is in effective control of the site.
Creating a favourite environment
To establish trees successfully, a weed-free zone should be created and maintained
around each tree until the tree is large enough to look after itself. The size of the
zone varies with both the species and the size of the tree, and must expand with the
tree as it grows-it is often easier to create this larger zone at the time of planting.
Weeds must be kept well under control until the tree has become established.
The point at which a tree is regarded as established varies with the species; generally
it is when the tree is:
from 1.5 to 3 m tall
vigorous, with full foliage and a stout stem
-
incapable of being topped by adjacent vegetation.
This could take from 6 to 12 months for fast-growing species- for example,
eucalypts - and from 18 to 20 months for slower growing species.
The general site must also be maintained throughout this period to avoid
competition for the tree, to provide access and to reduce the risk of fire.
Steps in weed control
The following procedure will ensure that your trees become successfully established
without the threat of weeds.
I. Examine the site
Determine whether there are any features of the site that could contribute to a future
weed problem. The best time to deal with possible future problems is before you
plant, because afterwards consideration for the well-being of the tree will limit the
methods you can use.