I’ve been doing some weeding. This is in our British garden where the weeds are always jumping at this time of year, especially when it’s been so wet and it’s been unwise to get on the soil.
I’ve also been having a clear out, bringing files and folders out from the back of the file cabinets and what did I find? My weed collection, three fat folders of pressed plants, that I made when I was a student at the Royal Botanic Gardens at Kew in London almost forty years ago (below right, click to enlarge).
And the first pressed plant I found in the first folder I opened was the same plant I’d just been pulling out of the garden: hairy bitter cress (Cardamine hirsuta). We have a close relative, Pennsylvania bitter cress (Cardamine pennsylvanica) in our American garden.
And this brings me to my first rule of weeding: our top weeding priority should always be to pull out are the weeds that are in flower or developing seeds. Hairy bitter cress rarely grows more then 10in/25cm high but can still can produce 700 seeds and fling them 31in/80cm, but it can also produce seeds when just two inches (5cm) high. So pull it out. Now.
Many of the traditional rules of gardening have little value but “One year’s seeding makes ten years weeding” really is true. Dandelions (below), which as annoying in Pennsylvania as they are in Northamptonshire, can produce over two hundred seeds in one seed head. So - obviously - don’t let them seed.
My second rule of weeding is always to shake the soil off the roots after you pull out the weeds and before they go on the compost heap or (in those cities with green waste recycling) in the green waste bin. You can ship out a huge amount of good soil if you’re not careful.
And my third rule of weeding is this: get them when they’re young. When nasty perennial weeds like bindweed come through at this time of year, a one inch shoot is often an indicator of yards of root underneath. Later, when their twirling stems become entwined with our garden plants, it’s all but impossible to remove them. It’s so much easier when they’re just an inch high and, at this time of year, if you disturb the plants you’re trying to protect when extracting bindweed roots they’ll soon settle down again. By the time the bindweed is strangling your cistus (top) it’s far far FAR too late.
My final rule is this: Don't spend half a day weeding and then the rest of the week nursing your aching back. I did half an hour this morning and half an hour this afternoon and I’ll try to keep that up. But if I’d spent two hours forking out weeds at a single stretch this morning (as I was tempted to do) I’d not be able to get out there again tomorrow or the next day or the rest of the week. Little and often…
OK, it's time to get back to the bindweed and dandelions and the dreaded hairy bitter cress.
I’ve been doing some weeding. This is in our British garden where the weeds are always jumping at this time of year, especially when it’s been so wet and it’s been unwise to get on the soil.
Gardeners and botanists both use common names as well as scientific names when referring to plants. Using common names for plants is more widespread in North America than it is in Britain, even among botanists, and even though common names are often simply made up if there doesn’t seem to be one already in use. But common names are confusing. After all, there are more than twenty different plants, from around the world, that are called “bluebells”.
Native Americans must have had local names for many native plants when settlers first arrived in North America but the settlers didn’t bother to learn them and simply made up new ones - or, as with birds like the robin, transferred a familiar common name to a plant that looked vaguely similar to one from back home.
So when I saw a large mature sycamore (above) way across the Delaware River the other day, its white branches ghosting against the oaks and maples behind, I was reminded of this: in Europe, sycamore is used for Acer pseudoplatanus; here in North America sycamore is Platanus occidentalis. The leaves are very similar, so I presume settlers simply transferred the name. But surely, native Americans must have had a common name for P. occidentalis. After all, I’m told they used to tap it for sap in the same way as sugar maples.
In Europe, P. occidentalis is the plane tree and its hybrid with P. orientalis is a familiar city street tree. In Paris, large plane trees in the streets are pruned – literally – into a plane with all the branches parallel to the street and none overhanging.
The sycamore of Europe, Acer pseudoplatanus (below) - whose botanical name, by the way, literally translates as “the maple that looks like a plane tree”! - is a menace. There’s a huge one in our neighbor’s garden in England and its seedlings spring up all over the place. What’s worse is that they get their new roots down deep quickly so that even when they’re less than a foot high they can be tough to extract, especially between the cracks in paving.
I’d much rather have the American version.
Acer speudoplatanus image (above) © Jean-Pol Grandmont. Licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
The day the echinaceas died... It was yesterday. And this is how it happened.
Echinaceas, coneflowers, and especially all the fancy hybrids that have come on the market recently, like ‘Flame Thrower’ (above) and all the doubles (below), hate bad drainage in winter. That’s what kills them. But yesterday that’s exactly what they got.
On Sunday night the temperature in our garden here in Pennsylvania went down to -10F (-23C). So, after a temperature almost as low the night before, and low temperatures for a few days before that, the ground was frozen solid to a depth it was hard to assess.
And then it snowed. Not a lot, just a couple of inches and the whole garden looked lovely. But then, yesterday, Monday, it got warmer. A whole lot warmer, and quickly. By early afternoon the temperature had risen to 48F (9C), and the snow had melted and the top inch or two of soil had thawed out as well.
But because the soil was frozen down deep, all the melted snow just sat there on the surface, in puddles – it could not drain away because the soil underneath it was frozen. Our borders were covered in pools of water, yesterday, and they’re still there this morning.
And in those puddles of thawed snow are the crowns of our last remaining echinaceas (this has happened before...) – and echinaceas hate bad drainage. So those last few may well die.
Of course, this is not a phenomenon that comes into play in Britain all that much, or in parts of the USA where the winters bring less ferocious frosts. Because if the soil is not so solidly frozen, melted snow drains away and impacts much less on our, rather sensitive, echinaceas.
But here's what's important: it reminds us that, wherever we garden, it’s bad drainage in winter that prevents us enjoying the vast range of exciting new echinaceas for years and years after we first planted them. Which is a shame, because they really are gorgeous. As you can see.
It’s always intriguing to find a plant that’s native near our American home in Pennsylvania growing near our English base in Northamptonshire (and vice versa) and the other day a stroll by the River Nene not far from our Northamptonshire house provided an enjoyable surprise. Spotted touch-me-not or jewelweed, Impatiens capensis, was growing on the bank (below, click to enlarge).
There were only a few patches, all grouped near each other, and I wondered for a moment if I myself had inadvertently introduced it on my shoes as perhaps I did in Pennsylvania when it suddenly it turned up in our garden. I walk this same stretch of river every time I’m back in England.
Mike Grant, editor of the Royal Horticultural Society magazine The Plantsman, pointed out in a comment on my piece about this plant turning up in the garden that “it has the distinction of first being recorded in the wild by the philosopher, John Stuart Mill (in Surrey in 1822)” and it is now well established in Britain, though mostly a little farther south and west from where I came across it.
In fact, we’d been thinking that perhaps we have the wrong native Impatiens in our Pennsylvania garden. Touch-me-not, Impatiens pallida, is bright yellow instead of red-speckled orange and would show up more effectively from a distance. Tomorrow I’m going to collect some seed from the plants that I’ve seen a few miles from our PA home. In which case look out for it in Northamptonshire a few years from now!
Thoughts on another non-native Impatiens species next time.
We’ve been here at the house on the lake for thirteen and a half years, and it took my five year old grandson to find an insectivorous plant that we didn’t know we had.
Monty is mad about insects – and so, by association, insectivorous plants. He has pitcher plants growing in their kitchen in the London suburbs. So when he was exploring along the banks of our lake with his dad Carl (below, click to enlarge), he knew a sundew when he saw it because he has some in a pot at home. And he knows what they do to insects. He’s not at all squeamish and watched with interest while I hit the bass his dad caught on the head so we could have it for supper.
So it turns out that we have a flourishing colony of Drosera rotundifolia (above, click to enlarge), the round leaved sundew, growing on the bank of our lake. But they’re growing in an unlikely spot. They’re only a few feet from the water, even now when the water levels are very low, but they’re on an east facing sandy bank where the soil is actually quite dry. Not the soggy sphagnum which we associate with these plants. While there is some moss, some plants are growing in bare sand.
Most of the bank is overhung by low shrubs, so only a five year old is short enough to make his way easily along there and look closely at the plants. But for two or three feet at the point where this colony is happy enough to have produced quite a few seedheads, it’s much more open.
This is a plant that grows all around the world – in a band through the Northern Hemisphere that takes in much of North America, north and eastern Europe and much of northern Russia. In Britain, it occurs mainly in Scotland, Ireland and Wales as well as southern and south west England. It's found scattered across Pennsylvania, in our county (Pike County) it’s recorded from seven sites but surely occurs more widely than that. But it took a five year old to find it on our own property.
It’s purple loosestrife season here in Pennsylvania. Swamps and other wet habitats are vivid in its purple coloring (above, click to enlarge), in some places it looks as if it’s smothered everything. This colourful European native is generally viewed as a destructive menace and many millions of dollars are spent every year in a futile attempt to eradicate it.
In Britain, by the way, where purple loosestrife (Lythrum salicaria) originated, it’s far less common and is a popular plant for bog gardens with over a dozen named varieties, two of which have been awarded the prestigious Award of Garden Merit by the Royal Horticultural Society.
In North America, purple loosestrife is generally regarded as evil but part of its reputation derives from the simple fact that it’s so colorful, it’s so obvious that it’s there. If it had dull brown flowers no one would notice. Ken Thompson, in his important book that I reviewed here recently, put it this way: “Very tall people with red hair, big tattoos and conspicuous facial scars rarely have successful careers as bank robbers, and purple loosestrife has a similar problem: it’s just too conspicuous for its own good.” He goes on to emphasize: “Recognition of loosestrife as a problem was largely based on anecdotal observations, which are likely to be particularly unreliable in the case of a tall species with such bright, obvious flowers. This is a well known problem that standard textbooks warn against: it’s easy to conclude that an otherwise rather dull wetland has been completely taken over if you look at it when loosestrife is in flower…, even if a more careful examination would reveal no such thing.”
My local experience indicates that it does not necessarily spread once the first plant arrives, and that it can also decrease over time. On the lake where we live, I spotted two plants growing together about ten years ago. I checked the whole lake last week and those two plants are still the only ones present in spite of there being many suitable habitats all along the margins. Native swamp loosestrife, Decodon verticillatus, is far far more aggressive.
And in the swamp where I first saw it flowering colorfully it has declined, as it has elsewhere, and a striking feature is that native shrubs including dogwood (Cornus) and arrowwood (Viburnum) are establishing themselves on individual clumps of purple loosestrife.
And it’s not as if purple loosestrife is entirely useless for wildlife. It’s been shown that a number of native species are more likely to grow in habitats containing purple loosestrife and in a study of over 250 plots it was found that there were more birds in those with purple loosestrife than in those without. I’ve seen around thirty individual butterflies on one plant and over sixty insect genera use it, including adult monarchs (left, click to enlarge). Birds even nest in it. Another significant study that looked carefully at this issue found that there was no difference in species richness between plots with and those without purple loosestrife.
Ken Thompson says, as he concludes his discussion of the issue: “Persecuting loosestrife is, and always has been, a waste of time.”
I was tempted to pull out those first two plants that appeared at the far end of our lake but I just left them and kept an eye on the situation. Ten years later they’re doing no harm.
Don’t get me wrong. I’m not saying that anything and everything that could be, and is, invasive should just be left alone. What I am saying is that it’s not as simple as “native good, non-native bad”. Especially when you look at how fast US native swamp loosestrife (Decodon verticillatus) can spread and the monocultures that result.
Monarch butterfly on Purple Loosestrife (Lythrim salicaria). Image © Liz West (http://www.EWestPhotos.com). Used here under Creative Commons Attribution 2.0 Generic License.
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.
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.
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.