The aliens might be coming

Rhododendron x superponticum - beautifully strangling a lakeside at the Yorkshire Sculpture Park.

Whether it is kudzu vine strangling trees in Virginia, melaleuca throttling the Everglades or Himalayan balsam on the English river bank, invasive aliens are big news. Gardeners of course have a particular interest in them, as all too often they are responsible for the introduction and distribution of these plants in the first place, and in some regions, anything new in the garden is something of a potential Trojan horse.

A new book about invasives: plants and animals takes a nicely-balanced look. Where do camels belong? Its author, Ken Thompson is one of the best British writers on natural history. A retired member of staff at the University of Sheffield, he has worked on plant ecology for much of his life. I can't imagine a better person to keep a cool head on this topic. He is one of the key people behind the BUGS project which is looking at the relationship (or lack of it) between plant origin and wildlife in British gardens. He is particularly good at poking sacred cows with a science stick, and on occasion, as when he had a go at the fashionable pretences of permaculture, something of a cattle prod.

This is a very readable book and a balanced one. A key message is that many invasive alien stories have more bark than bite, that a species which may appear to be spreading may not be anything like as bad as it either appears to be, or the local press tell you it is. He does discuss some of the real horror stories, and does indeed recognise that aliens can be a very severe problem in some situations. Although if I lived somewhere where an alien species was causing real difficulties, I think I might feel the book didn't go quite far enough in recognising this. Some species really do destroy ecosystems. But, most don't and one of the valuable points of this book is pointing this out, and that over time many invasive plant species reduce in number, or start to get eaten by the local wildlife or infected by the local pathogens. 

One of the key points Ken raises is the cost and the impossibility of controlling many invasions. He discusses the whole new field of invasion biology. One can't help but get the feeling that there are a lot of people with a vested interest in keeping fears of invasives stoked up – a nice source of grant money for research/control etc. The implication is – don't throw money at things you can't do much about and keep it for things that either work or for battles that are really worth fighting. Invasives help keep journalists in business too, with lurid press stories often an opportunity for some covert racism – a topic which the book could have spent more time on. 

Being British and discussing invasives is a slightly odd position. Our flora has (like us) spread throughout the world, often aggressively. The turf-forming grasses of north-west Europe in particular – much of the native flora of western USA has been throttled by these aggressively spreading plants. Sounds like the effect of the European empires on global cultures. However the dense matt of growth these grasses form, and their ability to grow at low temperatures, does mean that it is very difficult to get invaded back. There isn't a single North American species which has become a problem here. The problems we have with our worst invasives (Japanese knotweed and Rhododendron x superponticum) are limited in geographical extent and pale into insignificance compared to the problems many other places face. Ken points out that some of our natives behave as invasives here, on home ground. As with my point about the nitrogen pollution fed nettles a few posts ago.

A recent trip to the US Pacific North West was an opportunity to appreciate just what a huge impact non-native and (in some eyes at any rate) invasive species make. It all depends on habitat. One of the wise points Ken makes in his book is that most invasive alien problems are in disturbed habitats. Any kind of succession process that starts taking a vegetation back towards what might be found naturally there will inevitably reduce their impact. Out in the open in the PNW you see a lot of European aliens, but few in the woods. In an area where thick conifer forest is the norm you could argue that any bit of open land is disturbed. Much grassland, in the Columbia River Gorge for example is populated by European turf grasses, and spattered with the European cornflower (Centaurea cyanus) and vetches, the native California poppy appearing in much lower quantities. It was almost uncanny how much of the open habitat was composed of 'interlopers'. But this kind of grassland is largely a human artifact, so should it surprise us that it is full of non-native species? None of which by the way was dominating anything else and incorporated many natives too. It all looked uncannily 'natural'. 

Eurasian vetch Vicia cracca and European grasses make a meadow in Oregon, but natives seem to join in too, but what was here before?

California Poppy - Eschscholzia californica in habitat with the far more common european cornflower, whose presence seems largely benign. This is south side Columbia river gorge, near Hood River.

Inevitably I think about what is escaping from my garden. Geranium x oxonianum 'Claridge Druce' is scattering itself into the hedge bottom. I have often seen this species escape. I suspect it will settle down to evolve into a true species and a widespread component of the British flora. With its parents from northern Spain and Italy, it is effectively a neighbour and can be expected to settle down decorously. Persicaria amplexicaulis has, somewhat surprisingly, taken up home in the hedge bottom too – funny as it never seeds in the garden. Its habit is much reduced compared to how it grows in the border and hardly has spread at all. Its scarlet spikes look oddly at home though. It is Senecio fuchsii which I think will inevitably take off. A tallish yellow daisy, it lights up woodland edge habitats from one of Europe to another, except that is did not get across the English Channel in time after the last ice age. A native really. In fact I think we can say that any north European plant is effectively a native for this reason, as they would almost certainly been here before the ice scraped everything off. The senecio seeds like crazy in the garden and will no doubt one day wander into the woods, where really it belongs. There is little in the wild flora that flowers in shade at this time, so pollinators will probably be really glad of it. Maybe it just wants to come back home.

Senecio fuchsii (S. nemorensis) good but slightly tatty as a garden plant, great in light shade.

SUPPORT THIS BLOG

I write this blog unpaid (of course) and try to do two postings a month, to try to provide the garden, wildflower and plant-loving community with information, inspiration and ideas. Keeping it coming is not always easy to fit into a busy working life. I would very much appreciate it if readers would 'chip in' (as we say in England) and provide a little financial support. After all, you pay for magazines and books, and it is only for historical reasons that the internet is free. Some money coming in will help me to improve quality and frequency, and to start to provide more coherent access to hard information, which I know is what a lot of you really want. So – please donate now!! You can do this through PayPal using email address: noelk57@gmail.com

Thank you!

And thank you too to the folk who have contributed so far.

********
If you like this blog, why not check out my e-books, which are round-ups of some writing I did for Hortus magazine back in the early 2000s, along with an interview with the amazing Beth Chatto. You can read them on Kindle, or Kindle packages for smartphones or the computer. You can find them on my Amazon page here. You will also find my soap opera for gardeners - currently running at eight episodes.

Telling the story of UK naturalistic planting to Japan

        I was asked recently to write a piece summarising the recent history of naturalistic planting in Britain for the Royal Horticultural Society Japan journal. So I thought I should share the untranslated version.

  

The garden at home in August.

      Naturalistic planting in Britain arguably started in the 18^th century with the landscape movement, in which the grounds of country houses were laid out in a style that evoked a semi-natural, pastoral, landscape. This movement largely concerned itself with the large scale, the main ingredients were woodland, lakes and extensive areas of grass – the latter usually grazed by livestock such as cattle or sheep.

      The first person to promote a naturalistic style of planting on a smaller scale was the writer and magazine publisher William Robinson ( 1838-1935) with his book The Wild Garden, published in 1870. This book was however not based on real experience, and although much discussed, had relatively little real impact. A contemporary of Robinson, Gertrude Jekyll (1843-1932), chiefly known for her colourful perennial border plantings, promoted a naturalistic style of planting for woodland.

Early summer -

A very fertile and moist soil means that strong-growing perennial species need to be chosen to form a solid canopy of vegetation through the growing season. Perennials grow amongst occasional shrubs and bamboos.

       The success of Jekyll's woodland planting points to a key issue which has affected the development of naturalistic planting in Britain. With a long and cool growing season, open areas in Britain are dominated by a very competitive grass flora. In some shade however, grass growth is reduced, and other perennials and small bulbs are able to grow with less competition. For much of the 20^th century the most successful naturalistic plantings were to be seen in light shade.

 

 

      During the last quarter of the 20^th century, new approaches to naturalistic planting developed. There was a growing interest in growing British native plants – however the flora is relatively restricted, and is of only limited ornamental garden value. More influential, and arguably the most influential movement of all, has been the concept of 'wildlife gardening', where gardens are seen as mini nature reserves, supporting biodiversity. This encouraged a more relaxed, less tidy and desner style of planting, more tolerance of some weedy native species, and an awareness of the role of trees, shrubs and perennials together creating habitat for birds, insects and reptiles.

       Wildlife gardening fitted easily into a relaxed style of gardening which had been developed by an older generation of gardeners, particularly the use of long-lived perennials and small shrubs promoted by the popular garden writer Margery Fish (1892-1969), and the work of Beth Chatto whose garden in the relatively dry county of Essex, just north-east of London stressed the choice of plants based on their habitat preferences. Chatto was one of the speakers at a conference in 1994 at Kew Gardens to discuss new developments in naturalistic planting; the event brought together a number of speakers from The Netherlands and Germany, as well as the UK.

Plantings at the Queen Elizabeth Park by Prof. James Hitchmough. Photographs: James Hitchmough

A mix of plants of South African origin include species of Agapanthus, Dierama, Diascia, Kniphofia and Galtonia. Originating in the mountains of the Drakensberg, there is a long history of growing these species in Britain, but this is the first time they have been used in this large-scale way. This is midsummer. Credit: James Hitchmough

         From this time on, an informal grouping of gardeners and landscape professionals began to actively promote naturalistic planting. For the first time in European gardening, there was a real sense of cross-border communication. My own book, The New Perennial Garden, published in 1994, and a number of book collaborations with Dutch designer Piet Oudolf, helped publicise new ideas about plant selection and combination. Whereas old-style perennial plantings had tended to use highly-bred, high maintenance varieties, the new planting used long-lived species, often close to their wild ancestors, and shorter-lived species which would survive in plantings through seeding. The idea of the border as a narrow strip of planting, was challenged. The wildflower meadow was an inspiration, and plantings created where the viewer looks across a blend of flowering perennials and grasses.

Credit: James Hitchmough

       During this time, more British gardeners began to visit places on the European mainland where the new planting could be seen, for example the parks of Amstelveen, near Amsterdam's Schipol Airport, which used native plants, and the parks created in German cities through large-scale garden shows. An important role has been played by two academics in the Department of Landscape at the University of Sheffield: Nigel Dunnett and James Hitchmough, who are primarily interested in public space. They argued for 'enhanced nature', naturalistic plantings which offered city dwellers a stylised version of nature with plenty of colourful flowers, either combining native and non-native species or which were based on natural plant communities, foreign to the country, but which worked well in the British climate. Of these, the North American prairie has been particularly important; many of the species popular in perennial borders for the last century were in fact of prairie origin. A number of cheap seed mixtures of annuals developed by Dunnett have been commercially successful, whilst a number of gardens he made for the Chelsea Flower Show have brought his name and his idea of the wildlife-friendly sustainable small garden to public attention. He has also promoted the use of plant communities for green roofs and sustainable drainage schemes.

      Hitchmough's approach has perhaps been the most radical. He believes that the most successful plantings are those which are started from seed. The density of seeded plantings helps to exclude weeds, and allows a community of plants to develop which have a natural, rather than a human-imposed, set of relationships with each other. His work is based on a rigorous application of plant ecology science, and his doctoral students engage in work which looks at various aspects of the creation and maintenance of what are essentially artificial ornamental ecosystems. Maintenance has to be extensive, i.e. applied to all the plants simultaneously, so for example the time of mowing may be used to reduce the growth and spread of more vigorous species, and the use of a flame gun to simulate the burning which is a key part of the management of semi-natural prairie and other grasslands.

      For private gardeners, this rich variety of ideas, influences and methodologies, has proved a stimulating source of ideas. Whereas as once upon a time gardeners cleared away dead stems at the end of the year, now many leave them for several months, to appreciate their beauty in winter sunlight and as a source of seed for wild birds. Species which seed are now more likely to spread themselves through plantings, creating an atmosphere of natural spontaneity (and occasional unruliness). There is a greater willingness to create small areas of native plant community, such as miniature wetlands adjoining ponds or meadows of rough grass and wildflowers which may be only a few metres in extent. Even small areas of aggressive weeds such stinging nettles (Urtica dioica) may be left, as they are a vital food source for some species of butterfly larvae.

A mix of European wildflowers created by seeding, which flowers in early to mid summer. Normally, the flowering species would be a minority component of a community dominated by grasses; here the grasses are not included.Credit: James Hitchmough

Based on a North American plant mix, species of Aster, Heuchera and Rudbeckia flower in mid summer. 

 Credit: James Hitchmough

     Designers, as well as private gardeners, are now more likely to create blended plantings, imitating the pattern of plants in natural environments. There is an irony that one of the best publicly-accessible examples of this is to be seen, not in Britain, but in Hokkaido, where the British designer Dan Pearson has created a series of blended perennial plantings at the Tokachi Millennium Forest near Obihiro. The planting style here, and its sensitive management by gardener Midori Shintani, offers Japanese visitors a good insight into an exciting and beautiful new way of using plants.

More on the Tokachi Millennium Forest later!

SUPPORT THIS BLOG

I write this blog unpaid (of course) and try to do two postings a month, to try to provide the garden, wildflower and plant-loving community with information, inspiration and ideas. Keeping it coming is not always easy to fit into a busy working life. I would very much appreciate it if readers would 'chip in' (as we say in England) and provide a little financial support. After all, you pay for magazines and books, and it is only for historical reasons that the internet is free. Some money coming in will help me to improve quality and frequency, and to start to provide more coherent access to hard information, which I know is what a lot of you really want. So – please donate now!! You can do this through PayPal using email address: noelk57@gmail.com

Thank you!

********
If you like this blog, why not check out my e-books, which are round-ups of some writing I did for Hortus magazine back in the early 2000s, along with an interview with the amazing Beth Chatto. You can read them on Kindle, or Kindle packages for smartphones or the computer. You can find them on my Amazon page here. You will also find my soap opera for gardeners - currently running at eight episodes.