Circular raised beds with a path to the center (a slice of the circle cut out) are called keyhole gardens. Often the center has a chimney of sorts built with sticks and then lined with feedbags or grasses that allows water placed at the center to flow out into the soil and reach the plants roots.
Number of anchors per board: (Usable Length / Spacing for anchors) - 1. For my beds, I need 7 separators for each 8 foot board and 3 for each 4 foot board.
A 4x4 foot garden bed, for example, will have 16 planting squares (because there are 16 square feet in a 4x4 bed). A 4x8 foot garden bed will have 32 planting squares.
Vegetable garden bed construction materials should be chosen carefully. Some concerns exist regarding the use of pressure-treated timber. Pine that was treated using chromated copper arsenate or CCA, a toxic chemical mix for preserving timber that may leach chemicals into the soil which in turn can be drawn up into the plants, is a concern for vegetable growers, where part or all of the plant is eaten. If using timber to raise the garden bed, ensure that it is an untreated hardwood to prevent the risk of chemicals leaching into the soil. A common approach is to use timber sleepers joined with steel rods to hold them together.