A question about a raised bed kit.

[metroace]

This is my first posting on this forum. Be gentle!

I am shortly going to construct a bought timber raised bed kit some 30 inches high. Even though this kit will have been treated with a safe timber preserving porcess, should I line the raised bed? And if so, what would you recommend?

[Lesley Jay]

Hi Metroace! Welcome to our forum!!

That's a good sized raised bed! If it was me I would line the raised bed with a weed suppressing membrane which should stop any compost leeching out.

[metroace]

Thanks for that answer. Next question.

Given that I have that 30" of depth to play with, how much rubble/drainage would you recommend in the bottom before adding topsoil and compost?

30" is a great height for a raised bed. I have some small brick built ones at that height already and it gives you somewhere to put down your glass of ale while working!!

[richardwil]

Hi

30" is a lot. I grow in a 6 inch deep bed on a lawn and dont reckon any roots get down more than 18 inch. Most go down a few inches, things like parsnip and carrots about a foot, at least in my experience.

I feel you should get away with 18 inches of rubble but I would try to level this and then put a thick weed membrane down before adding a soil mix to keep the soil from working its way down into rubble and loosing some over time.

One problem though may be a lack of worm activity as they are unlikely to work through the rubble to get to the soil. I would add some from the rest of the garden.

Hope things work out.

[malcolmx]

unless you are growing potatoes this is a bit high i would make 2 about 15 inches high i would only place membranes on the base to stop weeds from growing up then about 1" of gravel or shingle and then fill with good quality top soil. if you removed lawn turves to make the beds then put them turf down on top of the shingle etc
if you are not growing carrots or or other root veg i would put in 3" of mushroom compost on top of the drainage or the turves if you are not planting till the spring cover with membrane and sow 1 month earlier than packets say in spring and cover with fleece . membrane will warm the bed and fleece will keep it in

[metroace]

Okay, so the bed has been built and put in place. I have a bad back which is why I like my beds raised as high. So please no more folks telling me that a few inches is sufficient.

Next question is another that might save my back some agony. Is there any problem about using broken up polystyrene blocks as drainage in the bottom of my monster beds?

[whitedragon]

i would not use polystyrene blocks not only will they take about 900+ years to rot
they leech toxins into the soil id use old bricks

i know with your bad back that it will be harder to do but really polystyrene blocks are not good
mate

[metroace]

Okay, is there any safer solution out there that is also lightweight?