Depending on the height you want to achieve, you can either use finer rods and plant them with a distance of around 20-25 cm /8-10 inches between them for fedges of up to 5 foot (i.e. 8-10 rods per running meter for single rod fedges) or you can use heavier rods, planted with around 30-40cm / 14-16 inches between them for higher structures (i.e. roughly 10-12 rods per running 2 metres.) In addition to this you might want another 4 rods (woven together) every 2 metres, if you don't use fence posts.
(To save yourself constant measuring, cut a piece of willow or any other stick to the required length and use it as a spacer.)