The Green Roof: lessons from the first five years

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This is a visual catalogue of how my green-roof developed over its first five years, following its initial planting in Autumn 2009. My intention had always been to establish a low maintenance bio diverse plant community of drought tolerant garden plants. I now know that this is possible, but looks more like a weedy wild meadow than a garden.

This initial experiment was a success in many ways, as the beautiful photos below show, but by mid-2015 it’s ecological direction was clear: self seeding grasses and annual weeds were destined to win. More than half of the plants varieties I had tried to grow became extinct. Several garden varieties I had not planted turned up and ran riot. The whole area was becoming a seed bank that was infecting the surrounding garden. But I had learned some important lessons and had enjoyed its unfolding beauty along the way.

Phase two will require a complete overhaul based on the lessons learned first time round. It will be more garden-like, less wild, but more manageable long-term. I hope. So this seems like a good time to summarise the evolution of the first phase of this unique gardening eco-system.

In a separate post I will report on how individual plants fared. And I plan a third post in which I will focus on some of the naturalistic plant combinations that, to my eye, were particularly beautiful and only possible when plants are allowed to follow their own ecologically inclinations and mingle naturally.

— 2010 —

Green_roof_Spr_2010
After their first winter, the new plants are looking fresh in early spring.

Green_roof_Summer_2010
Sedums, thrift and ponytail grasses in late spring.Green_roof_Spr_2010-5
Seed heads of pasque flower, pink thrift and sea campion.

— 2011 —

Green_roof_Spring_2011_8
Spring in the second year. The clumps are filling out.

Green_roof_Spring_2011_5
Overview showing most of the roof garden, looking North with a ladder to the back.

Green_roof_Spring_2011_6
View looking South. Hardly any weeds yet.

Green_roof_Spring_2011_7
Notice the open areas like a gravelly ‘path’, and the mounds of  golden thyme (middle-right)

— 2012 —

Green_roof_Summer_2012_1
The golden thyme has spread to form good dense mounds. Carex Evergold doing well.

Green_roof_Spring_2012_2
The open ‘path’ has developed a nice mossy cover. It’s looking more like a natural environment.

Green_roof_Spring_2012_1

This was the roof garden at its best: Many plants, knitted together into a magnificent tapestry, with low weed numbers easy to control. Notice, however, a seedling of ponytail grass, bottom left.

— 2013 —

Green_roof_Summer_2013_1
From a low angle it looks like a meadow. 
Green_roof_Summer_2013_3
The chives had appeared on their own and would try and take over.

Green_roof_Summer_2013_2
The pink Aquilegia to the back is self sown. Ragworts and dandelions appeared in number too.

— 2014 —

Green_roof_Summer_2014_5

The weeds begin to take over. Some from the more enthusiastic garden plants, others from wild plants brought on the wind or by birds. Weeding is now a major headache. See the dozens of ponytail grass seedlings.

Green_roof_Summer_2014_2
It’s still very attractive, but there are dozens of self sown grasses and chives. And dandelions.

Green_roof_Summer_2014_3
The hazy sea of tiny leaves are wild Dove’s foot Geranium with tiny pink flowers. Black medic weaves its stems through everything in a tangled mat. I’ve lost control: nature has taken over! Perhaps drought will kill off the weeds and the toughest ornamentals will survive?

— SUMMER DROUGHT + NEGLECT WHILE WE BUILT OUR EXTENSION —

Green_roof_Late_Summer_2014_2
Die-back from six weeks of dry summer weather. What survived? The large Sedums are OK…

Green_roof_Late_Summer_2014_1
…so are the Chives and ponytail grass, and a million weed seeds which germinate with the first rain :-(

— 2015 —

Green_roof_Early_Spring_2015_1
Iris bulbs push up through dead mounds of thrift. Weed seedlings are everywhere.Green_roof_Late_Spring_2015_2 Grape hyacinths soften the devastation. Between the grasses a tangle of weeds is getting ready to riot.Green_roof_Late_Spring_2015_3
The ponytail grasses are taking over. Their seeds germinate everywhere. If I don’t cut them back they will produce infinite seedlings.

— Summer 2015 —

Green_roof_Summer_2015_2 It’s still beautiful, but increasingly unmanageable. Green_roof_Summer_2015_3
Left to it’s own devices the ponytail grasses would make a turf-roof pushing out everything else.

Lessons learned

  1. A green roof is a tough environment for plants and there are going to be many casualties. The ones that cope are likely to become invasive if they self-seed.
  2. Ornamental grasses may self-seed. Cutting off the seed heads before they ripen every year might keep this under control, but it is onerous. One plkant setting seed can produce hundreds of seedlings.
  3. The huge area of soil is a magnet for weeds which once you lose control are almost impossible to get on top of. Again – let a batch set seed and hundreds of seedlings will pop up.
  4. Even so, the chaos that sets in can be very picturesque. The unique environment created by shallow, drought-prone soil favours certain kinds of wildflowers that produce a distinctive habitat. This is fine if you want a bio diverse wildlife garden, and don’t mind the inevitable seeds spreading
  5. Irrigation in dry periods is essential to maintain most garden perennials. A simple manual or automatic irrigation system would transform the success of desirable plants. Annual weeds are better adapted to summer drought, than most of the plants one wants to grow.
  6. Weeds will take over unless dense mound-forming plants are cultivated and planted close enough together to cover the soil in a few years – thrift and golden thyme worked well, whereas the sedums and low-growing perennials did the opposite, providing perfect shelter for seedlings to sow themselves amongst. One solution would be to cover bare soil around and between plants with weed suppressing fabric.
  7. Vigorous self-seeders, like chives and pony tail grass should be avoided, unless you want to let them take over and do their own thing. However, they act as an increasing seed bank, self-seeding into the surrounding garden beds, paving and paths profusely.
  8. Ecological plantings are only maintenance-free if you don’t mind them getting more and more wild, weedy and seedy.

 

 

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2 thoughts on “The Green Roof: lessons from the first five years

  1. Keir, hi

    I have just discovered your blog and love it, your beautiful photos (what camera do you use?) and your beautiful garden.

    I am especially interested in your fan-training of fruit. I have just seen your photos of the fan-trained Brown Turkey and would love to do something similar with the fig I purchased at the beginning of the Summer, which I planted against a sunny South-facing wall. I wonder if you removed any figs and leaves on yours before extending the branches with canes?

    Keep up the wonderful work.

    Much appreciated.

    Tim

    • Thanks for the kind comments Tim.

      My camera is an old Olympus E1, one of the first generation digital SLRs, and a pass down from my son, who is now a Director of Photography in the film industry. It’s only 4 megapixels, but the lens quality is good, and it shows that higher Mp is not necessarily better, or necessary! The zoom lens helps isolate close up shots nicely too. Not being a photographer, I usually run it in auto mode – but it does the job well enough for the blog!

      The only leaves / fruits I have removed so far, are those that project backwards towards the canes. Hope your fig experiment goes well.

      Keir

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