I understand blackberries grow on 2nd year vines. Will they come again in the 3rd year? If not, do we cut them back?
I actually had one vine that produced in the first year, well after the main season was over.
No on the third year. They will normally die after they fruit on the second year anyway, so cut them back to make room for the new shoots that will already be up by then.
Blackberries send up new canes each year, late spring, early summer, they emerge, grow - establish new canes, leaves, some branching… These new canes are called Primocanes… again noting on them but new canes and leaves and late season can develop lateral branches if pruned properly.
Once they go thru a winter, the next spring, those new canes that grew last year are now Floricanes, and they produce flowers and fruit… once they fruit and all fruit is done that year… they are “Spent Floricanes” and they die, and are pruned out of the patch completely after that.
But while those Floricanes are blooming and fruiting…
New Primocanes are coming up and getting established too (they do that every year).
So mid summer (after your first year) your patch will include both fruiting floricanes, and establishing primocanes. It can get a little crowded then… But after your floricanes finish fruiting, they will die and you can prune them out of the patch eventually. Some wait until dormant (winter) to do that.
So… first year canes grow and establish… second year canes flower and fruit, then die.
While your second year canes are flowering and fruiting and eventually die… you have more first year canes coming up and establishing…
Now there are some newer varieties that can actually fruit on first year canes (Primocane fruiting varieties). Prime Ark Freedom is one such variety. I have not grown any of those yet… but I do grow Everbearing Raspberries, and they do that too…
They send up primocanes that establish during spring and summer… and then in the fall they flower and fruit on the top 1/3 or so of the canes. So with primocane fruiting varieties, you get some fruit on first year growth, normally in the fall.
Then they overwinter, and the next spring, early summer, the bottom 2/3 of those canes, flower and fruit. So with everbearing raspberries first year you get some fruit in the fall, and then the next spring/summer on those same canes you get fruit again. (double crop).
I think the Floricane fruiting blackberries do something very similar to that.
After the 2nd crop they are done, and can be pruned out… and your new canes are establishing, and will produce some fruit that fall… and again the next summer.
Hope this helps.
Some blackberry varieties will grow very long fruiting spurs near the base of the older canes, then bloom and set late fruit, giving the appearance of a first-year fruiting cane.
And of course there are the primocane-fruiting varieties.