Building the flower bed
Most raised beds are built using 90 cm by 1.5 m (3 by 5 feet) landscape timbers and nailed together with 15 cm (6 inch) landscape nails. To start, if you are building on dirt, stake out the area and dig down 3.7 cm (1 1/2 inches) so the first timber is halfway into the ground. Stagger the seams of the timbers as you stack them. Make sure they are level before you stack on the next row. Nail the ends together at each level with the landscape nails.
Once you have the bed to the desired height, lay landscape fabric in the bottom and up the sides about 5 cm (2 inches). This will prevent most weeds from coming through your bed. If you are building on something other than dirt, you may want to completely contain the flower bed. This can be accomplished by building a frame with the timbers at the bottom and laying 6 mm (1/2 inch) plywood on top of the frame. Nail the plywood in and continue with the stacking of the timbers. Instead of landscape fabric you can use a membrane made for use in shower pans, or any heavy plastic sheeting. Place in the bed, fold the corners and staple near the top of the bed. Do not staple near the bottom or it will leak.
The soil you use will depend on the flowers you are planting. Most commonly, if the beds are more than two timbers deep, the first half of the bed can be filled with any kind of dirt. The top half is filled with a mixture of soil made for flowers and topsoil. You can also mix in your own special compost. Mix the soils together and fill the bed.
Plant with plenty of room for proper growth. It may look sparse when you first put in young plants but it will fill out and be beautiful in no time. If you plant too close together larger plants will end up crowding out the smaller ones and killing them. Plant the tallest plants toward the back and work your way to the front with smaller or draping flowers. You won't need to water the plants with the plastic lining as much as the dirt bed because the water will not drain out of the bed. Water as the plants' instructions indicate and add some fertiliser or fresh compost once every two months.