Hi Lilian if you have just planted them and they are summer fruiting raspberries the canes that would have flowered and fruited this year should have been cut right back before they were sold to you. New canes will grow this year and need to be stopped around the 5 foot mark and tied into wires to support them. Next year the canes that grew this year will fruit and new canes will grow. After this year's canes have fruited next year they need to be cut back to the ground the new canes (which will fruit in 2014) pruned to 5 foot and the whole process starts again.

Left to their own devices like brambles raspberries will just grow longer and longer canes.

Sorry forgot to answer the how many years question. We have raspberry roots that are at least 15 years old and still doing great!

I have heard of plants more than 20 years old, too. Do keep them in hand, though, or you will have a real "B'rer Patch" to deal with!!

We had a thicket of wild raspberries near where we lived back in the 70s, it covered a huge area!