Yes, you should stake. Drive the stake in at an angle of about 60 degrees from the ground (or 30 deg from the vertical) so that the stake crosses the stem of the tree at (as Tim says) approximately one third height, and secure at that point using a proper tree tie. The principle is to kep the lower stem and root secure while allowing the upper stem to flex.
As Tim says, maintain for 3 years.
Don`t be tempted to put a lot of manure under the trees when planting - just mix in a bit of compost and plenty of bonemeal.