by Cathy Krar, Master Gardener In Training, SCMG
The key to sweeter, bigger and juicier raspberries is PRUNING.
Raspberries left to their own devices are their own worst enemy. It becomes a matter of crowd control and they behave like unruly weeds. When there are too many bushes competing for sunlight, the leaves and berries on the lower part of the bushes die. Not only are they competing for water and nutrients, but lack of social distancing leads to disease, mold and blight. The result is smaller poorer tasting fruit.
Once you understand that raspberry canes live for only 2 years, then it becomes easier to figure out the growth cycle. The roots are perennial, but the canes are biennial. Green primocanes occur in the first year and form fruiting buds.
In the second year, the the floricanes bear the fruit. As the berries ripen, the floricanes die. You should resist cutting these back until late winter or early spring, as they send carbohydrates to the roots. Make sure to cut the dead canes right to the ground. Cut back anything that looks weak or diseased. You leave only the healthiest looking canes. It may leave your rows looking sparse, but this promotes more vigorous growth in the long run.
The recommended row width is 1-1/2 to 2 feet. Limit the number of canes to 3 to 5 per linear foot. I put stakes at the end of the row about 3 feet apart…and attach wire 4 feet off the ground to help support the canes. (And always leave the new green shoot growth alone!)
It is a good idea to tie up the primocanes to a trellis or wire.
The ones you tie up this year, are the ones you would remove the next. I would also work some compost into the soil to improve moisture retention.
The bottom line … A yearly thinning allows plenty of sunlight to penetrate the bramble and makes it easier to pick the berries too.
For more in-depth information: Fine Gardening Magazine Issue 144. Article by David T. Handley