They take up a lot of room and need a fair bit of attention what with tying the new canes down to a support and cutting the old canes out in winter. Some types are HUGE - Himalayan Giant and Bedford Giant are 20 feet across when mature! Clearly thorny ones are more of a pain, literally, than non-thorny. They don't mind what soil as long as it is fertile and moisture retentive. If you live in the south and have mild springs then early types like Waldo, Adrienne or Fantasia are good. Also thornless Oregon Thornless.
There are also hybrids like Tayberries, Loganberries and Boysenberries which are less vigorous and thorny so better for small gardens.
I don' t think you get a lot of choice as to the age of plant you can buy. They take a couple of years to get going but are worth it in the end.
Waterbutts is right - some varieties grow huge! This is my 3 year old 'Apache' thornless one, on an 8ft x 6ft frame:
Close-up of developing fruit:
When they say plant 2m apart, they mean it!
Hi Alan, yes, good to eat straight from the plant when fully ripe and great for pies, jam etc and do have very large fruit. I also grow Loch Ness, which is similar in all respects - pictures of those two and lots of other varieties on this page:
...no hedgerows near you then Alan...? the wild ones taste so much better, in my opinion... cultivated blackberries I always find quite bland in comparison... and all that trouble to grow...
I grew thornless Boysenberry up an arch, I did like the large mauve flowers very much...
also a Medana Tayberry but that's quite thorny... I think you can get thornless ones now but I think you lose some of the flavour...
...it surprises me that anyone grows blackberries to be honest, unless you've got a really big plot and live in town....however, best of luck with it, if it's what you and family want there... I doubt you'll have any trouble growing it...
Fantasia is excellent, large berries excellent taste and seldom find any maggots in the fruit unlike wild ones!
I grow mine on wires strung from scaffolding poles,the area is about 20feet long 7 feet high and at the moment 3 feet deep.
I do feed it well and prune very hard autumn with a light prune in early summer to keep it in shape!
Only draw back really, really wicked thorns!