Pond plants for bumblebees … on my roof terrace!

14 March 2022

By Katrina ‘Tree’ Thuis, Bumblebee Conservation Trust volunteer ambassador

I live in a top floor flat in East London and have a little roof-terrace, or as I call it, my bee-balcony!

Early in 2020 I had a problem with some of my planters filling up with rainwater, and a little voice inside my head started telling me that although weight restrictions on my building’s roof meant I couldn’t have a proper pond up here, perhaps this was Nature, nudging me to try out a bit of water-loving bee-friendly planting. What had I got to lose by listening to that little voice?

First, I had to read up a little on the differences between ‘bog’ plants and ‘marginal’ plants. I admit I used to mash them all together in my head and assumed they’d all be fine in the water. It seems that bog plants like acidic soil and to be damp but not permanently saturated, and marginal plants are fine with being in the water, but also with lower water levels, as long as their roots have access to it deeper down. I therefore decided that marginal plants would be the best choice for my purposes.

Did you know? ‘Marginal plants’ are called this because they often grow around the margins (edges) of ponds where the water is shallow!

My inadvertent attempts at cultivating an aquatic tomato plant had failed miserably… so I emptied out the planters for a new project!

I found a website which seemed to have exactly what I needed – a collection of 10 marginal plants, with the option of also including the soil and gravel needed. To be sure I was using the right stuff, I went for the full package. The plants are nearly all native to the UK and were selected with bees in mind. The plants also covered a long flowering period, which is one of the key things we need to bear in mind when planting for bees and other pollinators.

I cleared out two of the waterlogged planters (oh my, the pong was rather hefty!) and when my delivery arrived, I excitedly delved in to find a selection of baskets containing what looked like … mud. Perhaps a couple of leaves here and there. I lined them up outside and looked at them. How was this little lot going to keep my bees happy?

As I was documenting the experience for this blog, I ploughed ahead, determined to cover the highs and lows of the process, and began to place the pots into the containers I’d cleared out. If some of these were just twigs, then so be it. This was when I learnt my first lesson. I had underestimated the amount of space the plants would take up. Even channelling my finest Tetris skills, I just couldn’t fit all the pots into the two planters I had emptied out. Luckily, I was able to re-home the contents of another planter and use that as a third.

It should be noted that as I am in a top floor flat, this is not designed with general pond life in mind. If I had any chance of having frogs or newts etc visiting me, then it would be designed differently. I’d fall off my chair if I saw any amphibian here! And there’s no danger of hedgehogs or similar falling in, so I’ve not needed to install any ramps. This is purely intended to provide for pollinators, and if any of those decide to go for a paddle, there are plenty of stems for them to climb on to.

So which plants did I have…?

• Marsh marigold (Caltha palustris) – native, flowers March – June.
• Lesser spearwort (Ranunculus flammula) – native, flowers June – July.
• Water forget-me-not (Myosotis scorpioides) – native, flowers May – September.
• Blue flag iris (Iris versicolor) – non-native, flowers May – June (selected due to size for my planter).
• Purple loosestrife (Lythrum salicaria) – native, flowers June – August.
• Marsh woundwort (Stachys palustris) – native, flowers July – September.
• Gypsywort (Lycopus europaeus) – native, flowers June – September.
• Yellow loosestrife (Lysimachia vulgaris) – native, flowers July – August.
• Water plantain (Alisma plantago-aquatica) – native, flowers June – August.
• Flowering rush (Butomus umbellatus) – native, flowers July – September.

I also picked up a couple of oxygenating plants; some elodea and pepper grass.

Every so often I took a photograph so I could log how my endeavour was progressing. Those plants I’d described as ‘just twigs’ began to show signs of life, and over the months it all really started coming into its own. The transformation was so satisfying to watch unfold in front of me.

I admit, it wasn’t all plain sailing, and I had a bit of an algae issue at one point. I’d anticipated something like that would happen and had bought some pond snails which I hoped might help. I didn’t get them immediately, as I wanted some algae to build up for them to eat; I didn’t want to pop them in a fresh pot with nothing to get stuck into. At its worst, I used a bamboo cane and swirled it around as though making candy-floss to scoop it out. The warning would be to ensure that if manually removing algae, ensure you aren’t also removing any pond life such as your precious snails. I’ve read that popping what you’ve scooped out at the edge of the pond gives things a chance to climb back in. When I added my snails, there were one or two leaves of duckweed in with them. Now I have rather a lot of it, however, I believe its presence is helping to manage the algae, so I’m letting it be for now and just keeping an eye on the coverage.

So, did I get any buzzy visitors? Did my efforts please some pollinators? Yes. I am bee-lighted with the results of this exercise! I had at least three different types of bumblebee visit my marginal planters – the Buff-tailed bumblebee (Bombus terrestris) was first, followed by Red-tailed bumblebee (Bombus lapidarius) and Common carder bees (Bombus pascuorum). I’d not seen Red-tailed up here last year so was very pleased to welcome them back to my balcony.

I also had other insects and pollinators swing by; the ladybirds enjoyed the greenfly, and I had various hoverfly types too, as well as some tiny bees. I tend to assume that any tiny dark bee is a lasioglossum species of solitary bee, but am never confident identifying the small ones. Perhaps one day.

The purple loosestrife features in a LOT of my pictures, that’s because it has a wonderfully long flowering period. It started in June and in September it was still making my bee visitors happy. It is now one of my new favourite bee-friendly plants. I’m certainly getting a lot of ‘bang for my buck’ from it.

So there we have it. I had a bee in my bonnet earlier in the year about setting up a pollinator-friendly marginal habitat in the skies of London and I had a stab at it. Is it something I would do again? Yes – it has been a fascinating journey for me. If I’m ever fortunate enough to move somewhere I can build a proper pond then I’d definitely do so. I did learn a bit from this exercise, and would like to share ‘Tree’s Top Tips’ with anyone interested:

• Don’t underestimate the space the plants will take up.
• Don’t worry if your plants don’t instantly impress – give them time.
• Select plants which will flower at varying points.
• Get some pond snails.
• Check the fill every so often and top up if rain isn’t forecast.
• BUILD IT AND THEY WILL COME!

Of course, being someone who enjoys planning the next project, I’m already turning my thoughts to what else I can do on my balcony!

Read more of Tree’s blogs on her website here.

More ways to help

Looking to create a bumblebee-friendly space? Check our our Bee the change resources here.