Tinkering with green sedum roof… bad idea?

[Koulibiak]

I have a green roof on top of my bin store. It’s the modular type with shallow cells, planted with sedums. It’s been there for a couple of years and it’s been fine - virtually no maintenance, other than getting rid of a few weeds every now and then.

But it doesn’t really look fantastic - the sedums are all low growing, and while there are no bald spots, it does look wow either.

I’ve been wondering if I can introduce some new alpine plants to it - aubrieta, Californian poppy, creeping thyme - that would cascade down the sides and add a pop of colour. Or maybe echeveria, which wouldn’t look so samey as all the existing sedums.

Has anyone tried adding plants to a modular green roof? If so what and how did you do it? My research online hasn’t given any answers.

I might pop a few Californian poppy seeds to get started, and maybe try and replace a few sedum cells with thyme and aubrieta, but I don’t want to damage the rest of the roof.

Any advice would be very welcome 🙏

To be honest, the only reason sedums do okay up there is because they don't mind being roasted bone dry for days on end in summer. Anything else is going to need watering to stay alive, and then the sedums will be too wet.

Really, even alpines? I thought they were happy with very little soil and water.

Alpines like cool temperatures, so I think they will fry in the summer heat. You could try some sempervivums to introduce more colour or explore plants that are associated with hot climates but are often hardy in the UK with very free draining soil. Maybe Delosperma? Or experiment with annuals grown from seed so you haven't wasted money if it doesn't work - Portulaca and Mesembryanthemum spring to mind, but there will be other options.

I'd also be tempted to try Lotus corniculatus. Very easy from seed, very drought tolerant and has showy flowers. In S. Yorkshire it grows in cracks in the tarmac! Good pollinator plant too. Creeping thymes would also be worth a try. Lots of cultivars, but I'd grow from seed in the first instance to see if it will survive. It's the shallow modules that will limit you.

US xeriscape planting sites might provide inspiration. Eriogonum?? Not sure without checking how much of a root-run they need…

Specialist semp nursery: https://www.craigiehallnursery.co.uk/

We have a sedum roof which we had installed 3yrs ago. It was a mix of about 7, different varieties. We were told that during the year, we would see differently coloured flowers, but this hasn't been the case. I suspect that several of the plant species have died off, leaving the hardier ones. I agree, ours doesn't have the wow factor at all!

This year, we have bought sedum seeds, vermiculite and a special fertiliser which we will mix and sprinkle on there this month. Apparently autumn or spring is the best time to do this. I shall report back if it makes any difference. I agree though, that the alpines would likely just die in summer.

I think alpines will be ok. We live in well the alps and have alpine rockeries and they all thrive fine in scorching hot dry summers ( and then under snow)

@JC03745 that sounds interesting- do you have a link by any chance? Thanks 🙏

do you have a link?

I bought the sedum seeds, vermiculite and fertiliser from a mix of amazon and ebay. I plan to mix them together, throw them on the roof and hope for the best! 😆

Sedum Mix | 1000+ seeds approx | Green Roof | Rock Garden | Same Day Dispatch | eBay

https://www.permagard.co.uk/sedum-roof-fertiliser not the link I used, but I bought the same osmocote product from I think amazon.

I bought a massive bag of vermiculite, again, possibly from amazon, because I can use it elsewhere, other than the roof.

Thank you! That’s my kind of gardening too 😊.

@Koulibiak What about some houseleeks (sempervivum)?