Defra’s five plants to mitigate flood risk. Do they really know what they are talking about?

Written by Mike Swan, Senior Advisor

As a contribution to Flood Action Week, Defra and Floods Minister, Emma Hardy, are urging us to cultivate flood-resilient plants in our gardens, and on 17th October, The Independent brings us the story: “Homeowners urged to use five key plants to make gardens flood ready”.

Living well above the spring line in chalk country, means my garden is pretty much automatically ‘flood ready’, apart from possible runoff to our winterbourne. But my curiosity was aroused, so I read on.

Surprise, surprise, one of Defra’s five was included in what I already grow. Red bistort (Bistorta amplexicaulis) was here when we arrived in 1993, and we would have struggled to eradicate it even if we wanted to. Its attractive red spikes are great for cut flower arrangements, but it is quite invasive and needs keeping in check. It may also like moist soils, but I can vouch for the fact that it does just fine on dry chalk, and yes the bumblebees like the flowers too.

So, what of Defra’s other four? They are River Birch (Betula nigra), Red Twig Dogwood (Cornus sericea), Mace Sedge (Carex grayi) and good old Yellow Flag (Iris pseudacorus).

Now yellow flag is one of my favourite plants; in full flower on the river bank at Mayfly time, it is redolent of the moment that spring turns into summer, and a joy to behold. It needs wet soil, but I have to confess that I fail to understand how it would help to make a garden ‘flood ready’, although I suppose its roots might help to stabilise the banks and reduce erosion if yours includes a river or stream.

The rest may also have helpful credentials and I guess that mace sedge could help to trap soil run off if your garden goes under. We are also told that these plants will soak up water like sponges, although I’m not sure if that helps much in the event of a real flood. On the other hand, a thicket of dogwood will soon shade out lower ground cover and if anything increase soil erosion risk. The same also applies to a quick growing birch, with the added risk that the neighbours might not like it if you cut off their sunshine.

What struck me more immediately was that I did not recognise the scientific names of most of these plants. My history in studying native plants and their pollination goes back five decades, and scientific nomenclature moves on, so I thought I might be out of date. But no, when I looked them up, I discovered that River Birch, Red Twig Dogwood, and Mace Sedge are all North American. I knew that Red Bistort was a garden plant and almost certainly a foreigner; in fact, comes from Himalaya.

So what goes on here? On the one hand, Defra urges us to nurture native flora and fauna, and on the other, it suggests we fill our gardens with non-natives to help reduce flood risk. There are plenty of native sedges that like damp soils, and would do just the same job as C. grayi. Meanwhile, the native Red Dogwood (Cornus sanguinea) would surely be just as effective as the American, and has equally attractive red stems to give colour in winter. Again we have two native birches (B.pendula and B. pubescens) that would surely do the same job as River Birch!

Come on Defra, lets have some joined up thinking here.

Comments

Use of the word WINTER BOURNE in the write-up

at 18:29 on 23/10/2025 by Eric T Smith

I had no idea until I entered that word in my computer search engine that the writer was referring to the stream, from what I read, at the foot of their garden. Living as I do some 13 miles approximately East South East I think along the A 6 trunk road in the place in Derbyshire named New Mills it is not a word commonly used in these parts and maybe others throughout England unless I am very much mistaken

Well done Mike Swan

at 16:00 on 21/10/2025 by Konrad Goess-Saurau

Well done Mike for pointing out the ignorance within DEFRA!! 30 years at Temple farm allowed me to experience their incompetence whenever one had to deal with them!

Flood risk

at 14:29 on 21/10/2025 by Michael Boxall

I think Defra would be better advising folk to remove concrete patios and other non porous surfaces from their gardens and in towns and cities where possible and plant the ground, any plants will be better than none at lessening soil erosion and run-off, but native species are of course most desirable. Rainwater needs to be able to soak in rather than run off into overloaded drains.

Resilient planting - argument over native vs non-native

at 11:33 on 21/10/2025 by Harrison

A well made point, and this comment is more in response to the 'non-natives' comment above which refers to a very valid point about planting non-native species in anticipation of climate changes. Counter to this point, on a visit to Kew Wakehurst (it is good to see they are exploring all the approaches across the Kew sites), one of the researchers there was researching a counter point to the concept of planting using species from 2-3 degrees south, or from hotter, drier regions to adapt to climate change. They were saying that we should be conscious of the plasticity and adaptability of our native species which may allow them to cope to a degree with changes in climate, as by brining in non-natives, while they may be more readily suited to hotter and drier climates, they do not have the same suite of adaptations that native species have developed to deal with all of the compounding factors of living in the UK, which extend beyond climate. So while it is tempting to go straight in with non-natives, awareness of the adaptability of our native species as well should be considered. Gardens are of course more isolated in what they are subject to and non-natives are likely better suited in these circumstances where climate is the main variable that cannot be controlled, with all others managed by the gardener. But care should be taken before non-natives are introduced as a means of 'adaptation' into more wild systems, when native solutions may be just as suitable.

Non - natives

at 12:41 on 20/10/2025 by Alastair

Your point is well made Mike, but perhaps this is a topic we need to consider further? On a recent visit to Kew Gardens our guide explained that they were starting to plant tree species from hotter, dryer regions, in anticipation of the likely climate here in 80 years time. Under natural scenarios of climate change nature has time to adapt, but this is human driven and taking place over a relatively short period of time of a few centuries. So we might have to take a more interventionist approach……like we do with game management?

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