Natives (American)

Book Review: Where Do Camels Belong? by Ken Thompson

Where Do Camels Belong?: Why Invasive Species Aren't All Bad by Ken ThompsonIn Britain, this invaluable book is subtitled The Story and Science of Invasive Species; in North America, the more provocative subtitle is Why Invasive Species Aren't All Bad. Both are appropriate; look dispassionately at the science and it’s clear that invasive species are not all bad.

So often, discussions of the whole issue of natives and non-natives (plants, animals, insects and the rest) are run through with the repetition of bold assertions, unproven by science, that it’s a relief to find a book in which the whole issue is viewed more calmly, in a broad context, considered over time, and backed by solid science. It's just what we need: more unbiased science and less thoughtless hysteria – and that is what this book provides. And it’s all presented in a lively, and very readable.

Ken Thompson discusses how we define “native” and how we stretch our objective definitions to take account of subjective impulses; he reveals how little we actually know about so many non-native species and how very few ever cause problems; he examines whether the most hated invasive species really are as destructive as we’re told and points out that some have positive impacts; he discusses how natives and non-natives can happily co-exist in the same habitat; he applies science to the myths surrounding invasive species.

One of the striking features of the response to the presence of non-native plants, in North America in particular, is the frequency with which they’re simply removed – just in case – rather than studied. As Dr Thompson points out, the proportion of non-natives that arrive in natural habitats and end up causing problems is minute. And when non-natives are studied over the long term, we sometimes find that their initial dominance is followed by a sharp decline followed by a stable balance.

I won't steal the author’s thunder by summarizing his invaluable discussion of how we define the word “native”, except to say that picking any date as a cut-off point after which an arriving species is declared an alien is clearly arbitrary and ignores the fact that ecosystems have always evolved over time and continue to do so. And suggesting that only new arrivals in natural habitats that are unassisted by man can be classified as “native” ignores the obvious fact that nowhere on the planet is unaffected by man’s influence, so nowhere is genuinely “natural” anyway.

So. What a refreshing book and one that’s full of stimulation and reminders to look at the evidence and not listen to the hearsay. This book effectively skewers the prejudices and pseudoscience of the plant police extremists for whom natives are, by definition, good and non-natives inherently bad. It should be read by anyone with an interest in native and non-native plants, by those working in the field, and also by natural history and garden writers like me - so we don't simply repeat misconceptions in our work. The book is stimulating and refreshing: as soon as I got to the end I immediately started again at the beginning. [The anwser to the book's title, by the way, is a fascinating one. Needless to say, it's not what you think.]

Where Do Camels Belong?: The story and science of invasive species by Ken Thompson is published in Britain by Profile Books. It will be published in North America as Where Do Camels Belong?: Why Invasive Species Aren't All Bad by Greystone Books in September. North American readers who are eager to read it before September can order the British edition from


Rampageous wisteria in the Pennslyvania woods

Wisteria floribunda smothering the Pennsylvania woods. Image ©GardenPhotos.comInvasive plants keep turning up on these pages, and often I’m less than supportive of the way the plant police want to rip out any non-native plants that turn up in wild places – as with the snowdrops I wrote about last month - whether or not they’re doing any harm.

Well, here’s one that we can justifiably worry about.

I spotted the bluish purple flowers hanging from the branches as I drove between the woods and the Delaware River in Pennsylvania the other day. That's Wisteria, I thought. I was on a tight schedule and couldn't stop, so when I got home I checked with the Pennsylvania Flora Project website which told me that no wisterias, native or introduced, grow in the area. The USDA plants website said the same thing.

Yesterday I was again passing that way and took a closer look. Yes, it’s wisteria – but the Japanese Wisteria floribunda (below, click to enlarge) and not the uncommon Pennsylvania native W. frutescens which flowers later and has much shorter strings of flowers. And it’s not just a plant or two, there must be half a mile of it in half a dozen different places over a stretch of a few miles. It's covering the trees(above, click to enlarge).

This is in the Delaware Water Gap National Recreation Area, where you’d expect some expert oversight of These strings of flowers of the Japanese Wisteria are longer and earlier than those of the native species. Image ©GardenPhotos.comthe habitat that’s being preserved, and one stifling mass of it is by the turn to the Pocono Environmental Education Centre. So why do the distribution maps say that it doesn’t exist in the area? I presume that, like the hellebores I wrote about a few weeks ago, it originated on a now-vanished property. When it was planned to flood this valley to create a reservoir many houses were vacated and removed - but not the plants. But it’s clearly been there a long time, so it’s strange that no one noticed -or, at least, no one reported it.

Of course, it looks spectacular but it completely smothers and weighs down the trees. Clearly anything growing on that scale – 30 to 40ft high, and more, through trees – must be doing some damage. I wonder if anyone has published any before-and-after wisteria research.

Virginia bluebells in blue - and pink

Mertensia virginica growing on a streamside in PA. Image ©
Driving close to where I spotted those naturalized snowdrops I mentioned here a few weeks ago – on my way back from my first session of cardiac rehab – I stopped for another look and found that the snowdrops, of course, were being overwhelmed by other vegetation including a star of our spring flora here in Pennsylvania – Virginia bluebell, Mertensia virginica (above, click to enlarge).

I haven’t come across lovely perennial this too often in this area but here it was growing in damp soil near a seasonal stream (dry at the moment). There were mature clumps, small plants and young non-flowering plants so it seems to be doing well.

Then, when I got home and was looking round the garden, I found that one of our clumps of the same plant A pink flowered shoot on a plant of Mertensia virginica in the garden. Image ©GardenPhotos.comhad produced two shoots with pink flowers (left, click to enlarge). Even on the usual blue-flowered plants the buds are pink, but soon mature to blue as they open. On these two shoots the flowers remained pink, though they seemed a little smaller than the nearby blue flowers.

White flowered forms with pale green leaves are also known, as well as plants with very pale blue flowers, and years ago I also saw plants with smoky bluish-purple purple flowers. They were all lovely. As soon as the clump sporting both pink and flowered shoots dies down in summer, I’ll lift it and split it to isolate the pinks. Not I just need to get my hands on the white one and the smoky one and the pale blue one…

There’s a fascinating chapter on these plants in Carol Gracie’s superb book Spring Wildflowers Of The Northeast.

Woodland native that's good in the garden

Anemonella thalictroides growing in an unexpectedly damp place. Image ©
Off out for my daily, cardiologist prescribed walk in the Pennsylvania woods yesterday, I came across two plants - uneaten by the deer that abound in this area – that while interesting to see in the woods are also good to grow in the garden.

The rue anemone, Anemonella thalictroides, is a lovely spring ephemeral, and a familiar native here in eastern North America where it’s often known as Thalictrum thalictroides - literally, the thalictrum that looks like a thalictrum. Surely that must mean that it’s an absolutely typical Thalictrum and meaning, I suppose, that all the other thalictrums are very definitely different.

Well, long ago that was the opinion. But in Europe and the rest of the world it’s now known as Anemonella thalictroides – in fact it’s considered so different from other thalictrums that it deserves a genus all of its own! This is a case of botanical science moving on and gardeners and botanists around the world taking their time to catch up.

Anyway, I was surprised to see it growing in soggy saturated soil by the side of a small stream as in these parts it’s usually seen in much drier conditions, such as trailside banks and rain-sheltered slopes.

You can see the wild plants I came across yesterday at the top (click to enlarge) but it’s true to say that their flowering season is very short – ephemeral indeed, so less useful in gardens. But like so many plants in the buttercup family - delphiniums, hellebores etc – there are many variants of Anemonella thalictroides and the double flowered forms make far better garden plants that the wild form as they bloom for so much longer.

‘Oscar Schoaf’ (below, click to enlarge) is a good example: not only are its flowers a rich pink, unlike the white or blush shade of wild forms, but they’re fully double so have more impact and last far longer than single forms. The problem is that plants are hard to come by, and they can be expensive. Propagation is by division - by scalpel!

Anemonella 'Schoaf's-Double' blooms for longer than the wild species. Image ©

Oh. I seem to have run out of time for discussing the other US native perennial that was such a standout – next time.

Distinctive trees of our local forests

Sassafras albidum (left) and Liriodendron tulipifera: two fine trees of the eastern American forests. Image ©
Two native trees of the eastern American forests have leaves which you just can’t confuse with anything else. Both feature fine fall color (although they're now past their peak) and both make fine specimen trees for gardens, on both sides of the Atlantic.

On the left in the picture (click to enlarge) the quirkily lobed leaf of Sassafras albidum. Kids call it the mitten tree, especially as seedlings may only have two lobes. We have a dying tree – one huge woodpecker hole is causing it to rot from the inside – but it’s inside the deer fence so its seedlings are popping up all over. Outside the fence – none.

Ours all seem to color yellow or orange, some with a few purple veins, but fall color on other trees can be a vivid red. And although we have plenty of seedlings they’re almost impossible to transplant. Suckers seem to work better. And it insists on acid soil.

The tulip tree, Liriodendron tulipifera (above right), seems more widespread across the river from here in New Jersey although there are a couple of young trees by the side of the road a few miles away and farther afield in Pennsylvania it’s moved in to take the place of all the chestnuts that died of blight. Again, its leaves are very distinctive – but very different – and its fall color is yellow to old gold.

Tulip tree develops into impressive straight-trunked specimens, the tallest in our state is 133ft/40m. Sassafras develops into bushier specimens, half the size.

Both these trees have many other valuable features, but as fall fades these are two of the most distinctive trees of our local forests and impressive in gardens too – if you have the space.

British gardeners can order Sassafras albidum from these RHS Plant Finder nurseries.

British gardeners can order Liriodendron tulipifera from these RHS Plant Finder nurseries.

North American gardeners can order both these trees from Forest Farm, and they're also sometimes available from local conservation groups.

Doll’s eyes and tulip trees

Actaea pachypoda, Doll's Eyes; the fruits weigh down the stem. Image ©
Just a quick post to show you these amazing fruits that we spotted on a woodland walk at the weekend. The plant is Actaea pachypoda, also known as Doll’s Eyes or, more prosaically, as White Baneberry, and we came across just one plant, its two shoots weighed down by these spectacular berries.

This is one of those plants that used to be seen far more often until the deer population grew so dramatically that in much of our area the ground flora has been decimated. The whole plant is poisonous, but that doesn’t seem to deter the deer. There’s an interesting discussion of this and the other North American Actaea in the exceptional Spring Wildflowers Of The Northeast by Carol Gracie.

In the garden this is a fine shade plant, especially when it's matured into a fat clump  - although here in Pennsylvania the fruits - which follow white fluffy flwoers - tend to rot before they reach their full glory; I think our plant is too crowded and overhung by shrubs.

The other fine sight at Tillman Ravine in New Jersey was a huge tulip tree, Liriodendron tulipifera, its fall foliage bright yellow high against the blue sky, way above the trickling creek. I remember the one at Kew, planted in 1770! Great to see such a fine specimen in the wild (but impossible to photograph).

In North America you can buy plants of Actaea pachypoda from The Tree Nursery

In Britian you can buy plants of Actaea pachypoda from these RHS PlantFinder nurseries

Powerhouse Plant For All Seasons: Clethra 'Ruby Spice'

Clethra alnifolia 'Ruby Spice' in flower and in fall color. Images ©GardenPhotos.comPowerhouse Plants, Plants For All Seasons, are individual varieties which provide color and interest for at least two seasons of the year and not just a fleeting flush of flowers followed by months of dull foliage. I feature over five hundred of them in my latest book, Powerhouse Plants, and every month in Gardeners' World, Britain’s top-selling garden magazine (and also available in the US) I focus on one very special Plant For All Seasons, highlighting three features which bring color to the garden at different times of the year. This month, in the magazine, I feature Hypericum 'Albury Purple'.

And every month here on my Transatlantic Gardener blog I bring you details of another, this month it’s Clethra alnifolia ‘Ruby Spice’ (click to enlarge), winner of the Royal Horticultural Society’s Award of Garden Merit.

‘Ruby Spice’ has two special features – three, if you count the fragrance. At about this time of year, the upright spikes of flowers are opening at the shoot tips and in the leaf joints of the upper foliage. Set against deep green foliage and deep rose in colour, they don’t fade as the flowers of older pink varieties do and they also feature a heavy sweet fragrance.

Then, in the fall, after the flowers have gone, the foliage turns bright buttery yellow to create an entirely different feature.

‘Ruby Spice’ is a very manageable plant, reaching just 6ft/1.8m, perhaps a little more, and forms an attractive bush without any pruning. It does, however, need an acid soil although it seems happy in full sun (as long as the soil is not dry) or in light or partial shade. Hardy to USDA zone 4 and RHS zone H5, it can even be grown in a large container of ericaceous (lime-free) potting soil.

This is my fourth monthly piece about Powerhouse Plants, Plants For All Seasons which don’t flare and fade with two weeks of flowers and fifty weeks of boring leaves. Last month I featured Rosa rugosa, and before that Kolkwitzia amabilis Dreamcatcher (‘Maradco’), Actaea rubra and Paeonia ‘Sarah Bernhardt’. So when you look at a plant in flower at the nursery or in a catalog, always ask: What else does it do?

Please take a look at Plants For All Seasons in Gardeners' World magazine each month. And check back here for monthly posts about other Powerhouse Plants – the Plants For All Seasons.

You can order my book, Powerhouse Plants in Britain from

You can order my book, Powerhouse Plants in North America and the rest of the world from

Or you can find out more about the book at the Powerhouse Plants webpage.

Subscribe to Gardeners' World magazine In North America,Gardeners' World magazine is also available in Barnes & Noble and other good bookstores.

What’s this scilla doing in a wood in New York?

Siberian squill, Scilla siberica, growing in Sullivan County, NY. Image ©GardenPhotos.comNosing around in the spring woods yesterday, near the east branch of the Callicoon Creek in Sullivan County, NY, I spotted a speck of sparkling blue, amongst fresh foliage and the flowers of Dutchman’s breeches, Dicentra cucullaria. Seemed odd. Took a closer look, and it was a scilla. There were a few leaves and three stems with one flower on each.

The map on the USDA Plants website reveals that the Siberian squill, Scilla siberica (left, click to enlarge), has been found in seventeen north east states but, according to the New York Flora Atlas, never before in Sullivan County. The little trail is part of the Stone Arch Bridge Historical Park, but few visitors pass this way. A quick check with the Pennsylvania Flora Project reveals that it’s been recorded in three places here in PA (For Brits: Pennsylvania is the size of England.).

It’s not native, it comes from Russia. So what’s it doing in a wood in New York? The nearest house – not, it’s clear, occupied by a keen gardener - is hundreds of yards away. In more than ten years I've only once heard of the creek flooding the area in which it was growing, so a flood is unlikely have dumped a bulb. So where it come from?

One flower was already developing its seed pod, which had weighed down the stem so that the pod was resting on the ground. That’s one way for the seed to spread a few inches. It’s growing about 10ft/3m from the narrow trail so seed arriving on footwear seems unlikely.

I often take a walk along this trail in spring, and have never spotted it before. Although the flowers may only last a few days, in hot weather - it can easily reach 70+F/21+C in April.

So I wonder how it got there…?

Book Bullet: Spring Wildflowers of the Northeast by Carol Gracie

SpringWildflowersJacket500This is a fantastic book.

Discussed in rich but readable detail, and profusely illustrated, are thirty of those beautiful and fascinating spring flowers which mark the passing of the snow and ice and the sudden rush of new growth – and not just in the north east, but over much of the country.

Plant by plant, from baneberries to wild ginger, centuries of scientific research are brought together with decades of enlightened personal observation to present detailed accounts of some of our favorite plants. But not just descriptions, far from it. The ways in which these plants fit into their botanical families, their relationships with their habitat, their pollination, their seed dispersal, their medicinal and other practical uses – it’s all there.

And here’s the thing: we know we can trust its combination of science and experience not only because it’s clear that it’s written by a scrupulous fanatic! But also, from her years as a tour leader at the New York Botanic Garden answering the questions of visitors – interested, of course, but not necessarily knowledgeable – Carol Gracie knows how to present her fascinating material in a way that scientists will respect, and everyone else can understand (with occasional help from the excellent glossary).

The book is also packed with wonderful pictures. In fact my only criticism of the book is that, in places, there are too many squeezed on to the page. I don’t think there’s a dud amongst them, but sometimes the page is just too full.

I first looked at entries on plants I’d recently researched myself including skunk cabbage, Symplocarpus foetidus, where her account of the plant’s mechanism for generating so much heat in its early flowers that it can melt snow and keep insects cozy includes an important detail that I’d missed! And I was thrilled to discover that it’s the box turtle, wandering up to 60m a day, that not only distributes seeds of may apple, Podophyllum peltatum, but through keeping them in its digestive system for a week while it wanders also greatly improves their germination.

So… whether you grow these plants in the garden or simply admire them on rural (or sometimes urban) hikes, I’m sure you’ll find this book fascinating. If you need more superlatives, just ask.

Spring Wildflowers of the Northeast by Carol Gracie is published by Princeton University Press.
  • The habits and habitats of thirty familiar spring flowers revealed
  • Detailed but easy-to-read text
  • Huge number of exceptional pictures
  • Gardeners and wildflower enthusiasts will be fascinated
  • Not just for those of us in the north east US
  • Put it on the short list for plant book of the year


An unexpected jewel - Impatiens capensis

Impatiens-capensisTwoOne of the unexpected stars in the garden this summer was an American native weed – jewelweed, Impatiens capensis. I’d seen it growing by creeks in this area, of course, and I always thought it was an attractive plant with its sparkling, red-spotted, orange flowers (left, click to enlarge). But the nearest wild plants I’d seen were a mile or two away, so I suspect that the seeds that produced the plants in our garden came in on my boots.

So: “What was it doing growing in your garden?” I hear you cry. “It’s a weed!” Well, when I spotted a seedling, just a few inches high, I thought I’d not pull it out as a weed but just let it do its thing – the flowers being so pretty. That first year, we had just a seedling or two which, in a dark and dry part of the garden, produced just a couple of small spindly plants. But, every year, it seeded. We pulled out most of the seedlings - which is easy when they’re small - and left one or two to flower.

This year we never even spotted the seedling between shrubs outside the guest room window until it emerged alongside the indispensible Physocarpus Coppertina (‘Mindia’) and behind Weigela Wine and Roses (‘Alexandra’). It flowered for months, never dominating, but always there. Always sparkling.

Of course, now we’ve let that one plant grow to almost 6ft/1.8m high, it will have produced so much seed that next year there’ll probably be hundreds of seedlings. And, again, we’ll pull most of them out and leave just one or two.

But it just shows how an ignored and unadmired native weed can add colour and character to the garden tapestry – if we just open our eyes to its beauty.

You can buy seed of Impatiens capensis from Horizon Herbs in North America, and from Plant World Seeds in Britain.