When you plant flowering trees, you should remember that these will need a lot of room to spread their roots and be more established. Spacing between the trees depends on how big your tree is going to get when it's mature. • Small trees should be planted eight to 10 feet (2.4 to 3.0 centimeters) apart. • Larger trees need to be 20 feet (6.1 meters) or more away from each other and any building. According to the SFGate Home Guides, Further, you should make sure that your trees have enough space to grow upwards too. Their canopy may even spread far, so if you have power lines cutting across your property, keep the trees away from these power lines and other similar structures.