All plants need water! How much water depends on the tree itself, & the conditions. For example, with some species, too much water can result in “wet feet”, or promote superficial root systems. An investment in an irrigation system should be considered where there is a large number of trees. These are available today in all shapes and sizes – with plenty of expert advisors as well. Irrigation is better done in the evening, to avoid evaporation and sunburn.
Slow-release fertiliser is best for natives. This can be applied annually, at the end of winter.
Newly planted trees find it hard to flourish where weeds are a major issue. Try to have a programme in place to remove (or prevent) weeds on a regular basis, perhaps every couple of months.
Your trees may be frost tender, especially while young, so some care is needed to mitigate frosts whenever danger exists.
Pests may be a problem in your tree location. A 3-stake shelter (see below) with windbreak will keep some pests away – such as browsing farm animals. Rabbits, hares, and possums may need to be trapped or poisoned