How far can raspberry roots spread under a barrier?

I planted raspberries in my garden a couple of years ago. I like having them but they spread too much. I don't have another place to put them where they would by isolated by lawn so I've been thinking about puting a barrier of plastic with bricks on top around them to keep them from spreading more into my vegetable garden. How wide would this barrier have to be?
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allotment after I originally welcomed their arrival from a neighbouring garden. They'll be up through your lawn if they're not already. I think the answer is to grow them in containers.
Steve
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I think you mean "how deep". at least one foot. My barrier goes down 8 inches and I get several escapees every year (out of a patch that is 4X12 feet).
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I have been thinking about putting down landscape fabric around my raspberries to controll weeds. My patch is approx. 15'x50'. What would be best to put over the fabric? Would crushed limestone change the pH of the soil? How many tons of rock should I order?
Sincerely,
Stuart Pedazzo...but you can call me Stu!
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Stuart Pedazzo wrote:

..and I think you mean "how far". Crushed limestone will not change the pH much (concrete is more effective at doing that), unless you have a marginal pH to start with.I have covered the paths of my garden with the stuff and I am pleased with the result. But raspberries pop up 8 feet from the bed, easily. That is why it is better to stop them with a vertical barrier. Also, if you just want to make 4 feet wide paths around the patch, you will need 3 cubic yards or so. It will be a lot of work to move the stuff.
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