That’s the best part about having Raspberries, as opposed to Blackberries. They let you know exactly when they are ready to eat, since they come off the core with a tiny pull. 
I grew up in a California suburban home that had cultivated blackberries all along the perimeter fence. (And some boysenberries!)
When wintering over the berry bushes, I would usually start in late autumn, when some of the canes had started to die back. (around here, in the East Bay, many bushes bear fruit into October)
Use your clippers and cut back any vines that have gone brown. Then what I used to do is take any wayward vines that were pointing the wrong way, or encroaching on the rest of the garden, and weave them into The Established Berry Bush Line. Just gently take hold of the vine, and wrap it around and under a more convenient vine or two until it stays put. Blackberries propagate by both seeds and underground runners, so you have to keep an eye out for any that get too enterprising.
But anyway, interweaving the bushes like that tends to keep the fruit concentrated in one place.
You can never really kill blackberries. Their roots go down to the pits of hell, where they gather moisture from the tears of the damned.
The City of Sunnyvale has informed me that using white phosphorus grenades is frowned upon, especially on “spare the air” days. I don’t have any lasers portable enough to deploy in the garden. Guns are useless against them. Given those limitations, bladed weapons work best.
I tend to armor up, by first putting on a pair of nitrile coated gloves, then another pair of heavy leather gloves over those, then a pair of heavy leather welding gloves over those, then an old pair of hockey gloves. That way, only about 20% of the razor sharp thorns get through to my skin to inject their payload of concentrated pain. Then I grab my Fiskars Brush Axe in my right hand, and a machete in the left, and I start going through some fighting forms. This serves two purposes: one, to intimidate the vines and convince them I mean business, and two, if they’ve managed to get their leaves on firearms they’ll shoot me Indiana Jones style while I’m still out on the lawn. If they were to surprise me with the the gun while I was in the thicket nobody would ever find my body. This way, I figure I’ll drop where the paramedics can easily get to me.
Once contact is made with the enemy, it’s important to keep swinging. Any pauses will give the vines time to grow back, and that hesitation may be fatal.
You will find that your blades dull quickly, both from the acid-for-blood that the vines use as sap, and from striking the bones of neighborhood pets and children that the vines have claimed. It’s important to have a bench grinder already set up and spinning so you can get sharpened and back into the action quickly. Perhaps that bit should be moved earlier in these instructions.
When you can no longer carry on, it’s best to admit defeat and retreat, nurse your wounds, and amputate any limbs that may have been too corrupted to heal. A few days later you can get a long metal rake and remove the vine bits that look like you might have killed (the leaves will have wilted slightly), stuff them in your yard waste bin, and send them off to the dump. Now they’re someone else’s problem!
I have blackberries in my garden. It is impossible to kill them. Cut them down whenever and however often you like, they will come back and prosper. On warm summer days you can practically watch them growing - I’m sure the runners can put on a foot in a day although I’ve never actually conducted scientific studies.
I don’t know what variety my blackberries are, but they’re huge and they ripen very early: we usually have the first ones around the end of June or first week of July. There are also lots of smaller ones on separate plants which I assume are seedlings that don’t grow true to type.
I spent a whole weekend one autumn digging up great big football-sized rootballs of brambles, and the next spring they were still shooting up like I hadn’t touched them.
And yet supermarkets over here charge £2.50 for a tiny punnet of blackberries. If I could sell the fruit I get at that price then I’d hardly need to work all summer!
Edit: and I am in England, so I would disagree with Mangetout saying they are not a problem here. My variety seems to be a very different animal from the feeble wild variety you see in hedgerows. I think they are some sort of Triffid hybrid. The fruit is far sweeter than wild blackberries, which I usually find very sour.
Buckgully, Best. Gardening. Story. Ever! I’m now going to read everything you’ve ever posted on this board.
Could be a cultivated variety (are the stems thornless?) - or the offspring of a cultivated strain.
Or it could be a naturally occurring hybrid with one of the other native species of Rubus - these are often very vigorous.
Or it could be just a natural variety that happens to be strong (natural variability of seedlings is quite noticeable in blackberries.
Or it could be that the plant has its roots into something good - a water main or a sewer, the rich soil where a compost heap once stood, or maybe one of the bodies you tried to hide.
When I was growing up in the Pacific Northwest, we also had an acre of land. It was covered half way with wild blackberries.
Over many years, I tried everything to rid my moms garden of these weeds. The only thing that I found to work was, FIRE! Yep, I cut them back and started a big fire on the stump/stems burning the branches and stems right on the spot. After burning for over three hours, they were GONE! They did not regrow in that area again.
I did miss the taste of these berries a little. When I got a craving for the taste I just went down the road a bit and picked them from the brambles at the side of the road. Yes, the pies are wonderful! I can taste them now!
They’re certainly not thornless, they’re incredibly vicious. But the fruit is among the biggest blackberries I’ve ever seen anywhere - at least at one end of the garden - which makes me think they must be a cultivated variety. They are two or three times the size of wild ones, and very sweet and juicy, so I don’t want to get rid of them altogether. I just wish I could confine them to a neat and tidy area.
Not many things grow rampantly in my garden - the soil is basically sandy heathland - but these things pop up all over the place where birds drop the seeds and grow at a tremendous pace, so I don’t think it can just be one particular juicy bit of soil.
Maybe I ought to sell cuttings to fruit growers. I have a pretty small garden (40-50ft long) but the brambles down one side of the fence produce bucketfuls of fruit, even just from the bits I can easily reach.
Jesus. Here in the Pacific Northwest blackberries are an incredibly invasive species. They will take over everything if you let them. They can’t really get a toehold in mature forested areas, but let a field or yard or garden go for a couple of years and it will turn into a blackberry nursery. And pretty soon your house and car will be swallowed up too.
Any non-native blackberry on our property gets pulled up by the roots as much as possible, no point in chopping the stems if you don’t get the roots. No exceptions. And if we want blackberries, we just head down the lane a few hundred feet and pick as many gallons as we want.
Sorry, but this talk of cultivating blackberries is making me shiver a bit.
I have no advice about the care and nurturing of blackberries but I did come into this thread to whinge and moan about how envious I am. My Dad used to take me blackberrying when I was little and I haven’t had a decent blackberry since about 1958.
Doesn’t it suck!
I mean, going ‘blackberrying’ was a rite of passage back when I was a kid too. You learned damned quick how to avoid getting pricked and how to pick the ripe berries. You learned how to work in a team (one bends the cane over whilst the other drops the berries into a bucket), and you also learned how painful sunburn can be if you didn’t cover up during harvest! (My mum took my sister and I camping one year in Feb, and we all decided to go topless amongst the berries: if you’ve ever had sunburned boobs…)
Funny thing, while I always managed to pick plenty of berries, there never seemed to be many to take home.