Tag Archives: rooftop rewilding

Top rooftops for bees

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The rooftop garden at Bow Bells House in Bread Street, was found to be the third best rooftop garden for pollinators in the City in 2024 and the six best greenspace for pollinators out of all the private gardens surveyed in the square mile by ecologist Dr Konstantinos Tsiolis for the charity Pollinating London Together.

The result is a vindication of the important role roof gardens have to play in providing habitat to pollinators in urban areas. Moreover, it belies the notion that bees and other pollinators will not forage and possibly nest above a certain height. Bow Bells House garden is high up on the eighth storey. There are advantages to being high up, notably that unlike many ground floor gardens in the City, it is unlikely to be shaded by a tall building. Since pollinators are cold-blooded and need sunlight to warm up and create the energy to power their flight muscles, they prefer to forage on sunny rooftops than shaded courtyards.

Each garden or greenspace was scored against the following critera:

  • the value of plants as forage for pollinators throughout their lifecycle stages
  • suitable and well maintained nesting resources
  • pesticide use
  • monitoring
  • number of pollinator species/groups found.

Bow Bells House scored scored highly for:

  • a good diversity and abundance of plants for forage throughout the year
  • three small bee hotels mostly occupied
  • no pesticide use
  • regular monitoring
  • 15 different pollinators recorded on site during monthly visits in the summer, including Green furrow bees (Lasioglossum morio), Four-banded flower bee (Anthophora quadrimaculata), Wool carder bees (Anthidium manicatum), Red mason bees (Osmia bicornis) and a number of hoverflies, a drone fly and a cabbage white butterfly.

Steps to success

I’ve created and maintained the two large planters on Bow Bells House for a few years now for Savills, which managed the office block. I was first invited to take over the maintenance of the planters and to improve the planting for bees in 2021. We added 2 bee hotels for Red Mason bees in 2023 after the bee-friendly planting was established and honeybee hives had been removed.

These are are number of reasons why I think the garden is such a hit with pollinators:

  • Unlike many rooftops it is not used for any other purpose other than pollinator habitat so it doesn’t have to look neat and tidy or to be landscaped. (That is not to say that a neat, landscaped roof-garden can’t be just as good for bees, but it has allowed us to experiment more).
  • I’ve been able to experiment with different plants to see which thrive in the conditions and provide the best forage for pollinators
  • I have allowed ‘weeds’ that have self-seeded to grow if they provide food for pollinators, such as gorse and thistles
  • I have prevented certain plants and ‘weeds’ from dominating – this takes hard work and time
  • It has a timed irrigation system so plants thrive even in drought conditions (before the irrigation system was installed we lost plants because the shallow depth of the planters means the soil dries out very quickly)
  • Honeybee hives were removed a few years ago so that other pollinators could forage without so much competition (however there are hives nearby so there is still a preponderance of honeybees foraging on the roof).

In total 23 greenspaces in the City were scored for their effectiveness for pollinators in between May – September 2024. Of these, 10 were rooftops.

The full report of of the Greenspace Habitat Survey 2024 will be available next month.

The 2023 report is here.

More information about Pollinating London Together here.

Improvements that could be made to Bow Bells House:

  • Sand mounds – to see if they provide nesting sites for mining bees
  • Piles of wooden logs drilled with different diameter holes – to see if they provide nesting sites for other cavity-nesting bees.

Rooftop mix and match – rewilding and planting

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Eight months after we planted lots of new flowers (in response to the drought in 2022) on the roof 8 storeys up on Bread Street in the City, many are thriving, and have been joined by some blow ins – flowers that have arrived another way. Birds have deposited the seeds, or they’ve been blown in -like the yellow, dandelion-like flower above and the patch of Red dead-nettle below (middle), which is important food for long-tongued bees in spring, like Hairy-footed flower bees and Common carder bees. The red campion is back, despite removing most of it as it was taking over, and I want to have a diversity of flowering plants throughout the year to feed bees, not a dominant few.

I realise that I can’t just let the roof do it’s own thing, or else the sunnier planter would have been covered with nothing but Red hot poker (kniphofia). It absolutely loves it up there – in the heat, the wind, the cold, the rain. It is the hardiest plant I’ve ever come across.

It will be interesting to see if we see more bees visiting this summer than last year when there was much less diversity of flowering plants. In summer 2023, the survey of pollinators on the roof by Pollinating London Together found a furrow bee on Willowherb (Epilobium) – another blow in – as well as less interesting honeybees and Buff-tailed bumblebees.

PL’s  Greenspace Habitat Survey 2023 scored the roof 14/20. It scored 80% on diversity of flowers for pollinators. I’m hoping for 100% this year. But only scored 3/8 for number of pollinator species found on the days of the survey. I would argue that one day was too hot for most pollinators, and another was too windy. But they are the extremes that pollinators face on a rooftop in the City of London during the summer.

The first 2024 PLT survey is scheduled for 23 May, so let’s see how the roof fares compares to last year. I think it will be much more attractive to bees if the conditions are good.

Rooftop raised beds for bees

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April 2023

This area of roof 12 storeys above the City was originally earmarked for honeybee hives, but we explained to the client (a large real estate managing agent) that hives don’t do well in the City due to many factors including lack of forage, We suggested they transform the area (25m2) into a bee garden for wild solitary bees and bumblebees to boost biodiversity. They agreed. So we made wooden raised beds earlier this year to hold 300mm of soil/lecca, fitted a drip irrigation system in case of drought and on 5 April 2023 myself and Alex finally got up on the roof to plant a variety of tough, bee-friendly shrubs and perennials that will sequentially bloom from later this month through to autumn. We decided that the first planter would contain plants that flower late spring, the second planter by mid summer, and the third for late summer plants.

I hope the depth of soil, the bark chipping we used as mulch and the irrigation system will prevent the roots drying out and give the plants plenty of room to grow and spread.

Plants include:

  • Rosemary (Rosmarinus officinalis ‘Prostatus Group’ and Rosmarinus officinalis ‘Miss Jessopp’s Upright’)
  • Perennial Wallflowers (Erysimus ‘Red Jepp‘)
  • Hebes (pinguifolia ‘Sutherlandii’ and pinguifolia ‘Pagei‘)
  • Lavender (Lavandula intermedia x ‘Edelweiss’)
  • Vipers bugloss (Echium vulgare)
  • Perennial cornflower (Centaurea nigra)
  • Lamb’s ear (Stachys byzantina)
  • Korean mint (Agastache rugoso)
  • False dittany (Ballota pseudodictamnus or pseudodictamnus mediterraneus)
  • Sedum Autumn Joy (Hylotelephium ”Herbstfreude’)

We’ve also scattered seed balls over one of the fourth planters to create a wildflower raised bed. I’ve never tried this before, but because it’s a rooftop that is not used by staff or clients, I think we can get away with experimenting a bit, rather than having to focus on aesthetics. If the seeds don’t take, we can always plant more shrubs. Maybe an Strawberry tree (Arbutus unedo) for winter forage.

As well as bee-friendly forage throughout the spring and summer, we are putting in 2 x bee hotels for cavity nesting solitary bees. It will be interesting to see if we get any nesting so high up.

I will be visiting each month to maintain the planters and monitor the visiting bees so watch this space.

Summer 2023

Late summer planter full of Korean mint (Agastache rugoso) and wild flower planter with red poppies

Bees seen in the first year:

  1. Honeybees (lots from a neighbouring rooftop hive)
  2. Red mason bees on the wallflowers – we introduced some cocoons which hatched and the bees were foraging on April/May blooms. (pictured left)
  3. Common carder bees foraging on Echium vulgare in mid summer and Ballota (pictured right) in late summer.

A year on…..end of Feb 2024

The spring planter is blooming in late February with Wallflowers and Rosemary. It is looking a bit crowed. I think I put too many wallflower plants in! The mid summer planter is looking neat and tidy and ready to bloom in May/June.

The late summer planter has a few gaps as a couple of things didn’t do well. I may add a second Ballota as it is thriving. The wildflower meadow looks interesting. The Rosemary plant in the middle will provide early forage as wildflowers themselves don’t feed bees until mid summer.

The Centaurea nigra looks as if it is about to bloom (end of Feb!) and the electric blue Muscari armeniacum (Grape hyacinth) bulbs I planted in the autumn are about to appear. And the bee hotels, which I didn’t remove have a number of plugged tubes so it will be interesting to see when the adult males start to emerge.

We’ve had such a wet winter that I’ve not yet turned the watering system back on. I will keep an eye on the rainfall over the next few weeks to judge when it needs to.

Rooftop Rewilding

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Drought-resistant perennials planted in large, foot-high planters 8 storeys up on 1 Bread Street, EC4

This summer I’ve been rewilding office roofs in London to feed and house wild bumblebees, solitary bees and other pollinators. Two of the roofs overlook the City of London and aren’t accessible to people working in the offices.

Bee-friendly perennials replaced evergreen shrubs in planters on Carter Lane, EC4

One rooftop is in Soho and is frequently used by staff to hang out and have lunch.

Lush London studio rooftop 5 storeys high. Hexagonal planters with year-long bee-friendly flowers, W1

For a city law firm, we have worked with their gardener to improve the planting for bees and installed bee hotels where solitary red mason bees make their nests each spring.

Bee hotels installed on 8 storey roof terrace used for entertaining. Early-flowering rosemary and wallflowers, EC4

We’ve also rewilded window boxes and planted small trees for bees on rooftops.

Window box of Verbenas hung on roof terrace railings. Crab apple tree (Malus sylvestris ‘Evereste’) blossoming in a rooftop planter in the City

We judge the success by the bees and other pollinators visiting the flowers and nesting.

Top left clockwise: Common carder bee on Nepeta; Buff-tailed bumblebee on Nepeta; Red mason bees nesting in a bee hotel; Common furrow bee on Anthemis tinctoria; Hairy-footed flower bee on Nepeta.

Rooftop rewilding is part of a solution for companies wanting to mitigate climate change. We know the climate and nature are intertwined and we can’t solve one without improving the other. Rooftop rewilding is a local and tangible start by bringing more nature into cities and improving biodiversity. And it is a great way to engage employees and community groups through talks, workshops and ‘meet the bees’ sessions and to and enhance your company’s social value.

Bee spotting on roof terrace with Weil law firm; pupils from a local school supported by Weil take part in a bee hotel workshop.

Rewilded rooftops can provide nature-based solutions to flooding, heatwaves and pollution, as well as making cities more attractive to us as well as to pollinators. And corridors of rewilded rooftops would prevent pollinators being confined to small fragments of habitat and instead allow them to thrive by creating ‘bee-lines’ – a green super highway where each rooftop becomes a pit stop where they can refuel with nectar and pollen on the way to city parks and green spaces. (It has been estimated that up to 70% of wildlife species could go extinct if action is not taken to enable them to move through the landscape). 

If you would like Urban Bees to rewild your rooftop, or to work with your existing gardeners to improve planting for pollinators, we will happily pay a visit and provide a free consultation. No space is too small, from patios, to window boxes. Rewilding every grey pocket could help.

Contact: Alison Benjamin alison@urbanbees.co.uk 0788 4054150