>>2157716Really you shouldn't need any help. Brambles are easy as fuck, they're weedy and tenacious. If you take a length of vine and cover it with decent soil it'll shoot up through and you can divide that into as many plants as you want come fall.
I'm kind of an organic nazi, I like to just give nature lots of organic material and let worms and woodlice make my fertilizer for me, so I can't advise about additives but it's probably fine. Even if you burn the foliage with a bit too much what you're looking for is good roots and better growth next year. So read instructions and know what you're doing but you can probably go heavy.
