Making the hour’s drive back and forth to my cardiac rehab three times a week, and often walking woodland trails on the other days, I’ve spotted some interesting plants along the way.

A couple of years ago I wrote about a yellow-leaved form of common milkweed, Asclepias syriaca, which I spotted growing by the side of the road and last week in a quiet area at the back of the radiology unit (yes, I was just poking around…)  I found a yellow-leaved plant of a different Asclepias species – A. tuberosa, butterfly weed. As you can see (left, click to enlarge) it looks very dramatic and doing very nicely amongst the crown vetch (Coronilla varia).

There were also normal green-leaved plants scattered about the area, which had clearly been disturbed during construction work so we’ll see if that coloring was the freak result of something nasty in the soil or a genuine mutation. I’ll stop back later in the summer for another look.

White flowered monarda

Just at the moment our local wild bergamot, Monarda fistulosa, is in full flower. This seems to be a “first respondent” if you like, one of those plants that quickly arrives in freshly disturbed soil on open sunny sites. It occurs as a few plants or in huge drifts which, when you look closely, include an occasional plant with darker, or paler flowers.

But this week I screeched to a halt as I spotted a plant - just one - with white flowers (abiove right, click to enlarge). It turned out not to be the white flowered species M. clinopodia (which has a few purple spots on the flowers), but a genuine white-flowered form of M. fistulosa (wild bergamot). There were only a few plants in that location, but I’ve marked it and will collect some seed later.

UPDATE That was a few days ago - and yesterday I found another one, twenty miles farther south. I've been all these years and never seen one white one, and now I come across two.

Asian bush honeysuckles

I’d never stopped to look closely at all the shrubby honeysuckles along the roadside (please forgive my severe dereliction of botanical duty), they’re growing along a stretch of road where it’s not safe to stop the car. But they’re quite a sight in May when covered in white or cream or pink or red flowers, and again now when they’re in fruit.

Then in a parking area the other day I spotted a plant with lovely amber orange berries (left, click to enlarge). Frankly, I’m not sure if it’s Lonicera maackii, L. morrowii, L. tatarica, or L. x bella (the hybrid between L. morrowii and L. tatarica)  – all of which are collectively known as Asian Bush Honeysuckle; I’ll have to make more of an effort to check them when they flower next year. But, although I know they’re all rated as invasive, they’re very attractive especially those with brilliant scarlet berries (rather than a dull and dirty red) and this pretty amber berried form.

Variegated oak

And finally, on the way up the hill to the ledge from which I shot this wonderful picture of a field of Black-eyed Susans (Rudbeckia hirta) – a variegated oak seedling (below, click to enlarge). I think this may be the only one I’ve ever seen outside a botanic garden, and here it is growing by a woodland trail in Pike County, Pennsylvania.

It’s a seedling of red oak, Quercus rubra, and a quick online search for variegated red oaks reveals only ‘Greg’s Variegated’ and one named as 'Foliis Variegatis' in the Journal of Arboriculture in October 1987. It’s growing very near the trail; I may have to move it to the garden in the fall.

The only other one I’ll mention here is the vanishing trumpet vine (Campsis radicans). There are occasional plants all the way along my drive, all with the usual orange flowers. But, last week, I spotted one cluster of purplish red flowers.

There was too much traffic to stop examine it but it turns out this is a known variation - ‘Atropurpurea’ – but very rarely seen. So rarely seen, in fact, that when I did stop a few days later – I couldn’t find it!

There I was, driving along counting all the European plants growing - and often looking very attractive - along the Pennsylvania roadside when in the distance I noticed a whole field of orange. In this part of the world it could only be one thing: Black-Eyed Susan (Rudbeckia hirta). And so it proved, a large field covered from edge to edge in R. hirta, with a scattering of fleabane (Erigeron annuus).

This is in the Delaware Water Gap National Recreation Area, a park ripe with alien plants as well as natives and also very rich in bird life. But acres and acres of rudbeckia? It didn’t look natural. The park people had a hand in that, I’m sure, they must have sown seed. But it looks spectacular.

There were also three interesting features about the uniquely colorful field. Firstly, I spent two half hours, on two different sunny days, walking through the field and looking at the plants and I did not see a single insect of any kind feeding on the flowers. Not one.

And secondly, the flowers varied in shape noticeably: some flowers were very starry with narrow ray florets (the petals) and some much more full with broader rays; and many were in between.

Also, I noticed that on all the plants the flowers were bicolored: dark yellow-orange at the base and a paler tone at the tips (left, click to enlarge). That two-tone coloring is a feature of many garden varieties but the Flora of North America – the most authoritative work on North American native plants - is very specific: it says that the rays are “usually uniformly yellow to yellow-orange”. I’ve since checked other plants in the area and they’re all two-tone.

The Flora of North America also says: “or with a basal maroon splotch, sometimes mostly maroon”; I’ve never seen a wild plant with maroon flowers in the wild. But it shows that the rusty coloring of many garden varieties and the development of the first red flowered form 'Cherry Brandy' (below, click to enlarge) are based on an inherent genetic capacity for darker shades.

So, naturally, many people want to grow this colorful plant in their gardens. But, as a friend said to me the other day: “We keep planting them, but they never come back the next year.” The reason is that they’re biennial, and they die after flowering and you either have to sow more seed or hope they self sow. If you want a perennial form, grow Rudbeckia fulgida.

UPDATE: And here's a view of the field a few days later from the top of the nearby escaprpment, hundreds of feet above.

In 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 amazon.com.

           

Invasive 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 the 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.

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 had 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.

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!



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

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.

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 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 amazon.co.uk

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

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.

Nosing 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…?