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How deep do raised beds need to be?


i want to make a raised bed vegetable garden but am unsure how high/deep they need to be. The beds will be installed on top of an old lawn lined with weed membrane due to a horsetail problem. I could kill the grass off and the horsetail but don't really want to wait another year to start growing... Im hoping to grow potatos, carrots,parsnips, onions, garlic, runner beans, broccoli, swede and cauliflower. what would be the minimum depth suitable?

thank you in advance



  • A raised bed only needs to be as deep as you want it to be! Scaffolding planks are usually a good guide to depth, although if you want carrots and parsnips, it would either have to be very deep or you'd need a separate, smaller yet taller one maybe. You'd need a good depth too for potatoes, but they are quite easy to grow in bags

  • I'm afraid I don't think that membrane will keep horsetail out - the fine surface roots of the ash trees at the end of our garden grow upwards  through the membrane into our raised beds - horsetail will grow through tarmac image

    Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.

  • Thank you.


    That's food for thought Fruitcake I might mahe some smaller but deep ones for my carrots and potatos ????

    you have confirmed what I was dreading dove from above , about the membrane. I did get hold of some industrial strength roundup last year and it cleared  it from the block paving on the drive next to the lawn. I'm very reluctant to use it on the lawned area if I intend to grow food there after though??? One of the viburnum trees looks a little worse for wear this year and I suspect it absorbed some of the weed killer. Although the other trees nearby seem healthy still!!! 

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