Posted: 22/02/2017 at 11:41
I'm not keen on the 'rubble at the bottom' that many people recommend. Mixing grit through the soil is always more effective, especially if you get a lot of rain. A bed that depth won't have much room for soil if there's a lot of stuff at the bottom, and the rubble itself can create a sump in heavy rain - even worse if the ground below th ebed is compacted and excess water doesn't drain quickly. Just my personal experience.
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I understand your concerns Fairygirl, and I suppose it depends on the type of soil the raised bed is on, and on the depth of the beds. I've not had any of the problems you describe. If anything the rubble actually minimises the risk of a sump being created because it's so free draining.
My ground is also free draining which will have an effect. The biggest issue for me has been the amount of settlement of the soil, which has dropped about 6" since the beds were constructed. The beds are 8' x 3' x 2' deep so would have taken a massive amount of soil to fill without the rubble base.
Last edited: 22 February 2017 11:43:38