Laura:

To avoid confusion in how to care for your raspberries, you first have to understand how the varieties you are growing behave, then apply that knowledge to your particular climate situation.

You mention that your purple canes are so-and so tall, and your red canes are so-and-so tall, but you do not say whether that is new spring growth, or canes that grew up last season. Since you are in zone 5, I will assume they grew up last season. My own new raspberry primocanes are scarcely 8 inches tall, and I am in a much warmer zone than you.

The Prelude is an early bearing everbearer type, and in your relatively short season the primocanes should be wintered over so they produce early the following summer. At that point, they are called floricanes. This berry is also capable of setting a crop on primocanes later in the summer in zones with long enough summers. In MA zone 5 there may not be time for primocane berries to ripen, though I could be wrong about that. However, they will surely bear the following season as floricanes. Floricanes should always be cut down to the ground promptly after they fruit. Prelude canes should be topped at about 3-4 feet, and I do not understand why your canes, as you describe them, are only 1-3 feet tall.

Royalty is a red/black raspberry cross, and behaves like a black raspberry in its growth habit. This berry bears on overwintered canes only, and should be topped at about 3 feet or so, or a little longer if provided with support. Early in the floricane season, it will grow in fruiting laterals that will bloom and bear the berries. Do not allow these fruiting laterals to become too long, or they will overtax the cane and your berries will be small and scruffy. Prune them back to a foot or so, or even shorter if the laterals are thin. Laterals that are allowed to grow out unchecked will eventually touch the ground and tiproot, growing a new Royalty plant for you if that is of interest.

There is no "when" to prune that applies to all berry types and climate zones. You prune when your canes reach one of the indicated stages of development.

Don Yellman, Great Falls, VA

I usually prune out the suckers of the raspberries and clip back the laterals of the blackberries. Seems to work well. Less is more, bigger fruit.

Here is a link that might be useful: How To Prune Raspberries