One common error when planting out new trees is the urge to fertilise it straight away. It is highly recommended that you do not fertilise your new fruit trees or put fertiliser in the hole around the root zone as it can burn the roots.
The best time to fertilise is Spring when the tree has started to grow after winter.
We don't recommend any particular fertiliser but a good "fruit and flower" fertiliser is always a good start.
Make sure you follow the instructions on the back of the packet and don't be afraid to ask your local nursery for advice.