I am building a small shed with a heather/heath roof using low growing varieties that reach 10-15cm.

I plan to use 4 separate 60x40cm Euro trays, lined with soil barrier, so that I can lift these off individually to move the shed for maintenance. The trays will fit into a ‘box’ on the roof. The 22 litre trays would give a soil depth of 9-10cm once lined. I have left over astroturf that I'm using as liner which will ensure drainage and I'll add some pea gravel to this - giving 9cm of actual soil. This will weigh 20-25kg - I only weigh 40kg so that’s about my limit on a ladder.

I can control the soil and drainage, and I live in the Scottish Borders where heather grows beautifully. It’s a sunny position, sheltered very slightly from the prevailing wind, on a roof pitch of around 5 degrees. I have easy access for watering, feeding and weeding.

The overall height from the floor to the top of the heathers is limited to the height of the fence (as we don’t want to lose the view of the hill behind). So to optimise the shed space I need to minimise the green roof height. Adding deeper boxes later would not be trivial as I would need to shorten the shed.

Is 10cm sufficient substrate depth to support a well-tended 10-15cm heather/heath? Or will they want to root deeper to withstand the wind? I plan to mix Erica carnea and Calluna.

The standard advice of digging ground out for 30cm seems like it cannot apply equally to those that are tall and those that hug the ground. If 10cm is not sufficient, what’s the minimum soil depth I can get away with?

Edit: I am now intending to use a deeper euro crate that gives me 13-14cm soil depth over the drainage. The rest of the question remains - is 13-14cm enough?

  • Good question; if could include if proposed soil depth includes some coarse gravel in the bottom for good aereation & good drainage, could also be helpful. We encourage you to take the Tour, and browse through the Help center, to learn more about how the site works! Thank you! Welcome to the site! – M H Aug 22 '20 at 10:37
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    Thanks MH - welcome appreciated and I've added a comment on that. (I've got old astroturf plus pea gravel to put in the bottom which will provide the aeration and drainage - with 9cm above that for soil). I use SO/SE under a different account as a programmer, but I'll also take a tour in case much is different here. – Lindz Aug 22 '20 at 11:07
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    Heathers do best with constant soil moisture, though waterlogged soil may cause the roots to rot. Trying to achieve those conditions with a very limited soil depth could be a challenge. – alephzero Aug 22 '20 at 13:14
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    Thanks @alephzero - I have the option to add clay pebbles to stabilise the water content in the soil and/or water them twice daily - more in hot weather. Do you think the clay pebbles would be helpful - bearing in mind I'm also now leaning to adding at least a couple of cm as per MH's suggestion above? – Lindz Aug 22 '20 at 13:55
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    Thanks MH - I can get the standard containers in 12, 15, 17cm exterior depth. 40x40 won't fit my roof layout (and isn't a standard Euro container size - I want to use those as I can guarantee that there will be available replacements forever), and I think using twice as many 30x40cm would chop it up a lot, but the 17cm depth gives me a usable 15.5 internally, so probably 13-14cm of soil. At 33 litres they will be a bit on the heavy side but if they were dry I could manage and if not then I have nice neighbours. Thanks so much for the sanity check, I won't wing it on the 10cm depth. – Lindz Aug 22 '20 at 14:08

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