The biennial system employs the same technique of mowing dormant canes after they finish fruiting. Additional management in the biennial system includes the maintenance of narrow rows during the vegetative year of growth and the use of primocane suppression during the fruiting year. A trellis or support mechanism for the cane is a necessity, not an option. For many years researchers and growers have know that for optimum yield raspberries must be managed with a cane density of approximately 15 canes per metre of row. The reasoning behind this practice is based on the fact that raspberry plants can only intercept so much light.
Additional canes act as competition for the limited amount of light available.
The use of primocane suppression eliminates much of the competition by reducing the number and height of the primocanes. With more light available you can now double the amount of fruiting canes which ultimately increases the yield dramatically. The system will vary depending on whether you are starting with a new planting or adapting an old. If an existing planting is being converted, you must decide which rows or blocks of raspberries you would like to primocane suppress and fruit this growing season. Some growers mow every other row, while some alternate blocks.