Semi-mature trees will change a garden quickly, but they weigh more and are also taller so you have to consider the weight while roots gain their strength. So that is why staking or guying can sometimes be necessary. The key word is sometimes.
A similar concept is when staking or guying are required. If any of the following applies, you will likely need support:
Sites with exposure or wind (coastal gardens, open fields, hilltops)
Soft or loose filling where the rootball is mobile (sand, possibly gritted ground)
Heavy trees with a large top compared to the rootball
Trees planted late spring/summer (out of season) when roots have less time to take hold prior dry weather
Those hard-to-see full-grown specimens where just the slightest movement could snap new roots.
Support prevents any tilting associated with those rootballs and allows for the finer roots to find their way into soil. For Semi Mature Trees, visit Nature First, suppliers of Semi Mature Trees.
When it isn’t needed:
Staking isn’t automatic. You may not need it when:
A sheltered site with a not-too-tall tree
The rootball is correctly sized and the tree is properly planted.
This takes some of the pressure off from staking that tree when planting, as by the end if done well it means there is a nicely firm soil structure in which to set roots.
It won’t hurt to move a little bit. The trunk grows sturdily and the roots spread.
Common mistakes to avoid:
Ties that are too tight and rub against the bark or inhibit growth
Leaving stakes for the duration of growth to large (12-18 months typically is sufficient)
Perhaps padding the trunk so it cannot move one bit.
If in doubt, check with your supplier or landscaper what support structure works for the species (and tree size combined), as well as site conditions.