green walls ketch
This week I got a call from an up and coming architect, asking me to create a five by five metre green wall to finish off the small lightwell to a stunning period conversion in north London.

Green walls or ‘living walls’ have been big news in the design world for a couple of years now. They hold the promise of that lush, designer look but installed in an afternoon. So I’ve been hitting the web and the phones to see how much it really costs to install a green wall in your courtyard. Want to know?

You could of course go the DIY route using recycled plastic bottles, felt pockets or suspended grow-bags. This client wanted to swerve the Good Life approach and go for an off-the-shelf system.

There are now several UK firms offering the service, but I would advise picking one with at least two years’ experience and testimonials. We’re talking about a combination of hundreds of living plants and streaming water down your house wall… what could possibly go wrong?!

So focusing on a few well-regarded suppliers I began to gather prices.

Plants: most suppliers offer a tried-and-tested long-list of fairly standard shade-to-sun plants to choose from, at an average cost of £2.50 per small plant. The difference comes in the advice about how many plants are needed per square metre: lower end is 30, top end is 45… so plants work out at £75-£112 per m2. Fancy specimens will of course bump up the price further.

The system: Essentially these all seem to be angled troughs fixed in columns and rows, with channels to hold irrigation pipes and all set against a waterproof backing and filled with a light substrate (soil). Prices seem to match, at an average of £375 per m2. You may at this point want to scan back up to the part about felt pockets and plastic bottles. If not, read on…

The irrigation: This is where the differences between ‘simple’ and ‘high spec’ start to appear. At the basic level, your irrigation pipes are fed by a split-fitting to your outdoor tap and the mains water exits via your normal drainage system. We’re talking chump change for this, at £380. BUT… there are a few drawbacks:

1. What if your green wall is high up.. how will the water reach the top?
2. What about adding soluble nutrients to the water… won’t they potentially back up into my water supply?
3. Isn’t it a bit wasteful of water… and what about timers?

OK, with a five metre high green wall I’m thinking I definitely need a pump of some kind to jack up my (nutrient-rich) water and stop those £122 per m2 plants at the top dying on me. And if I have a pump, I may as well recycle that water. So now I need a pump, a tank, a timer and a special valve that separates my drinking and green-wall water. Which need youra utility room to house them. Then I’m introduced to the concept of multiple irrigation levels…

So those plants at the top? They’ll constantly be soaking..and the ones at the bottom will be thirsty as hell if I don’t split up the water feeds to ensure the wall is evenly watered throughout. This does only apply to larger installations, but it’s worth thinking about. The cost of the ‘high spec’ irrigation is £3,000.

Finally, maintenance: All the suppliers I spoke to strongly recommended an annual maintenance plan but the services differed. The simpler offerings suggested twice a year for checking the system and irrigation pipes, including turning off/on the tap at the start/end of the growing season. The higher spec was for at least four visits per year, which included checking and replacing plants (at cost) where necessary, adding nematodes and spotting possible future health issues. So costs here ranged from £1,250-£4,300.

At this point the client and I agreed it was a bit like taking on a large, silent pet.

One last thing; these ballpark costs were all provided without the suppliers having seen the destination courtyard (small, basement floor). Access into it and up the walls – scaffolding, cranes and faffing about time – will add extra cost, and should be ascertained by a site visit from your top two suppliers.

So in summary, a guide green wall price per square metre for a green wall in London (excluding vat, mind) might be:green wall price courtyard
Plants (average £94m2), plus system      £375m2 = £470 per m2
Irrigation                                                     £380 – £3000
Maintenance year 1:                                  £1,250 – £4,300

Total for my 5×5 green wall:
Basic           High-spec
£1875          £2812          plants
£9375          £9375          system
£380            £3000         irrigation
£1250          £4300          year 1 maintenance
TBA              TBA             tricky installation

£12,880      £19,487 plus vat

Did I miss anything? Should I have calculated differently? Let me know! But this was a really useful exercise to run through for my client as she decides whether the impact (fabulous) will outweigh the cost and upkeep (significant). I actually think it is… but then I’m a garden designer.

 

B&B Italia-green wall

Images from Deverill-Jenkins architects and B&B Italia