Reading this give info you need in link.
Keep clicking FORWARD at bottom of web page that give next page in that section. There some drawing that give before after look of plant. About all info on web should come from this 782 pruning is hedge trimming so reach berries fruits. You can prune Blackberries up to 7 time year so one are two pruning each year want get in right shape that 12 cane 6 foot to long that growth could have went into laterals. In my zone 8b growth stops at Oct. 20th.

Here is a link that might be useful: Black berry pruning

Raspberries in general do not grow as rampantly as blackberries.

Your new growth canes should have the top few inches removed when they are 4 or 5 feet tall. You can still do this (cut the 12-foot plants back to 5 feet), there is plenty of time in CA for the plants to put out laterals.

Not sure about your first questions. Prune out the entire plant when done fruiting, not just the branches.

Thanks for the responses. I will cut out the entire plant when done ruiting.

In regard to the 12 foot plants (there are 3 that long), i cut off the tips so it won't grow out any farther, what if I leave it at 12 feet, won't there be more lateral branches (hence more fruit) in a longer cane or will it be harder to grow lateral branches. Or why is 5 feet a good height?

Thanks.

Or why is 5 feet a good height?

At 12 foot cane get so heavy it brake off at crown fruit leaves lateral and 30 mph wind they be on ground and want take ladder to pick fruit. Don't allow cane to get that long before tipping bud out. A 12 foot blackberry plant takes Trellis 6 ft. high common Trellis material T-post after in ground 4 1/2 ft high. You use live learn method I did.

Gator is right. The only thing holding up your large canes may be the house. You can leave the canes at 12 feet if you can secure them against winter damage. Laterals can form at any distance. The 5-foot method allows you to train the laterals and keep the whole plant so fruit can be picked without a ladder! On some varieties laterals grow at an upward angle, making the plant even taller.

So i have 3 of these long canes like 10 and 12 feet, they're leaning over now. The canes are really strong, not sure if they'd break, and I'm in southern california, so there's no winter weather here really. They're leaning over and about 7 feet high, i was thinking of tying them to a trellis. I actually have two 9 or 10 foot canes this year with a lot of fruit on them, yes, they're hanging badly, but hanging from an adjacent tree with branches, so it's supported, but seems like there's quite a lot of fruit growing, probably over 200 or 300 on these two canes.

Should I just cut it back to 5 feet or 6 feet then? I guess my question was if it's longer like that will it produce more fruit, or not necessarily, if not, then I can cut them, but seems my two long ones i have now, have a lot. I of course am greedy and would want more so if cutting them back to 5 feet will give me even more, let me know :)

Another question i had was I have other very thin canes on this thornless plant sprouting out in other parts of the garden, not near the main thick strong canes. Will those grow to anything significant, or should i remove them? I was thinking of giving them away to a friend.

I have a throned one in another place in my garden too that has shoots coming up all over the place they seem quite thin, but perhaps because they're still in the premature stages of the first year's growth. Will leaving them hinder growth on the thicker more developed canes?

Thanks.

Thing to do cut tip out around height you want plant they grow 4 inches a day so can't wait to long before tip in 7 days can grow 28 inches pass point to prune.
If let lateral off cane grow to long you have less berries on that lateral if tip say after 2 foot growth then bud on lateral grow new lateral that need tipping etc. that second lateral grows and tip it then come third lateral tip that 2 foot and fourth lateral come on tip that fifth lateral grow at 2 foot tip that and six lateral grow tip that and 7 lateral tip that lateral and new lateral all these set fruit. lateral one two three four five six and seven it should be in of season year by this time. All lateral set fruit in 2013. This from one lateral off main cane so if main cane sets 10 laterals each produce as above pruning on each 10 cluster of 5 berries = 50 berries per lateral time 7 350 berries off on lateral off main cane time 10 equals 3500 berry fruits off one cane so answer yes pruning water sunlight and fertilizer makes more berries and make good photo for book cover. This what I have seen blackberry plant do of coarse seen less the total production of blackberry plant no one has come up with that answer.

Hello scuzzynutty,

Since you are serious about blackberries, perhaps you know that the first year canes (primocanes) bear little or no fruit, but in their second year, they are called floricanes, meaning flowering canes. They flower and give fruit, and once finished with fruit, they turn brown and die off. Only trim them once you are sure that they have started to die off.

But good news: The University of Arkansas has somehow come out with two varieties of blackberries which fruit the first year. The new varieties are called: 'Prime-Jan' and 'Prime-Jim'. Google them. It is wonderful. This fall, I will put in a large organic blackberry patch and in the winter, I will get me some of these new varieties. Been growing other Arkansas varieties forever. This will be something to behold. You might want to get some for yourself. I hear that these new varieties give a summer crop and a fall crop the very first year.

Here's to stained-black fingers!

As I typed above, you can retain as much cane as you can deal with. Blackberries will form laterals and fruit along the main stem for as far as they end up growing. Most people want to keep them "in bounds" and trellised.

Although not strictly a winter phenomenon, I wouldn't trust untethered, long canes to a Santa Ana windstorm. Or some nutty neighborhood cat trying to reach a bird.

If you can get some root along with those thin outlier canes, give them away.

Thin volunteer canes coming up some distance from the original planting will not affect the original plant's growth.

Help from Ohio. I have a 1/2 dozen 2 year old thornless plants on 3 wire trellis. Some of my primocanes are 8 to 10 feet long. Should I trim these back now or wait till spring?

Next spring pruning take away from berry production so don't do any pruning until after fruit next year. Pruning over this time year in future if want cane a certain length tip bud out at that length. you have a lot new growth next year be good if fruit on longer canes out of way from fruit.

I did not trim back the new growth for next year in the spring and it is very long. Do I need to wait until the fall to trim it or can I trim it back now? I've gotten a lot of blackberries from the old growth that I will trim as soon as they stop producing but it's the tall trailing ones that I'm concerned about. And they do not have thorns. I live in Missouri, if that makes a difference. Thank you!