You can in fact freeze blackberries if you want to get them food for a while.
Typically you will find that these berries will stay good in a refrigerator for up to a week, so those who want to keep them around for a while to make a nice jam with will want to put them in the freezer for safe keeping until they are ready to use them.
Before you put your blackberries in the freezer though, you will want to make sure that you put them in a tightly sealed freezer bag or container so that there is absolutely no chance of them being ruined.