raised bed

[Tasmanian Taffy]

Hi all, I currently have a large raised bed 3 mtrs x 2mtrs x 800cmtrs which I  am not using. I am wondering if this could be used as a plunge bed, it has been filled with a gritty raised bed potting mix. could I use this mix or would I need to replace it with sand. I have built a frame over the top and I can cover the bed with solar plastic. I would like to use it for as a plunge bed for some of my Iris. Any advise or suggestions would be greatly appreciated.Thanks in advance, John.

[Cfred72]

Hi John, there's no reason why this should not work.
Maybe you should explain the mix a bit more, put up some photos to see what it looks like.
Is your mixture well draining?
If you put in a pot and you water, the water passes through in just how long?

[David Nicholson]

John, if I were doing the same I would dig out about a foot of the soil; replace the bottom 4 inches with some good sized rubble (broken bricks etc) lay some good quality, water permeable, sheeting over this firstly to try to keep the worms out and secondly so that the sand topping doesn't wash into the soil below and then top it up with about eight inches of good gritty sand. Mind you, with my record I'd never get round to starting it in the first place.

[Tasmanian Taffy]

Thank you both David and Fred. In the bottom of the raised bed I laid a sheet of weed control mat, on top of this there is about 100 mm of blue metal (Granite) road base then three rows of agricultural drain spaced apart and running the length of the bed then a further 100 mm of road base on top of this.The Raised bet potting mix is a commercial blend from one of the local nurseries with a lot of added coarse grit so it has good drainage.I can fully or partially cover the bed when needed. I am attempting to grow some Junos Iris from seed and thought that I could use this as a plunge bed / cold frame once they have been sown in a few weeks time (Autumn here).Any further advice or tips would be appreciated.
Regards, John.