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March 2010

New US hardiness zone map launches soon!!

At last, the promised land is in sight!

USDA Hardiness Zone Map Image ©USDA The USDA (United States Department of Agriculture) is set to launch their new updated hardiness zone map soon. Yippee! We’ve been waiting for quite a few years now, the last update was in 1990 (left). So it’s great news that the new map, based on the latest climate data from more weather stations than before, will soon be with us. British gardeners take note: the Royal Horticultural Society is also currently looking at the whole issue of rating plant hardiness. So read on to get a sense of the issues.

So: “The Agricultural Research Service (ARS) is in the last stages of getting the map ready for release,’ Kim Kaplan of the USDA told me. “The new map is an interactive GIS-based (Geographic Information Systems) map designed to be web friendly. It will also be presented on the web as jpgs so those without broadband access will still be able to use the map.” They’re just sorting out a service to host the new map so that the vast flood of users doesn’t crash the USDA servers. And you’ll see why this has to be a web based service.

It’s going to be far more than just a printed map, with a number of positive changes. In particular, using a web interface will make it possible to see the boundaries between one zone and the next in far greater detail. The ARS has also developed a way of presenting hardiness zones effectively in areas lacking weather stations, especially in rugged parts of the Western United States.

“As a result,” says Kim Kaplan, “the mitigation of extreme low temperatures by nearby, large bodies of water will be visible for the first time, as will the presence of cold sheltered valleys and mountain tops, which are caused by elevation increases and other geographic features. The warming effect of asphalt and concrete of major urban areas will also be visible in many locations.” So, for the first time, the warming effect of cities will be reflected in the hardiness zones map. Isn’t that great?

And all this is based on the most up-to-date weather station data possible. “The 1990 map was based on weather data from 1974 to 1986,” says Kim Kaplan. “The new one will be based on weather data from 1976 through 2005. Also, more weather stations in the mountains of the western United States will be used in the new map.”

There will be no changes to the zones themselves, except an addition at the warm end. “The 1990 map had zones 1-11 a & b,” says Kim. “The new map will have zones 1-14 a & b…  Zones 12-14… have been added to the legend to allow tropical plant breeders and nurseries to provide zone information on when to bring such plants in, such as from the deck.”

The result is a map of twenty-two zones and subzones in steps of just 5F. That really is the sort of detail that all gardeners appreciate.

Musa basjoo,banana,outside Of course, this whole system can never be more than a guide. Other factors like soil drainage, exposure to cold winds are also important and snow cover. But, at last, we’re going to have a zone map that reflects recent changes in our climate. So you may find that you’re now in a warmer zone than you thought – and you can grow far more plants than you thought. Perhaps I can leave my bananas outside all winter in Pennsylvania (on the other hand…)

Have no fear: As soon as the new map goes live I’ll let you know.

This is just so good… I’m so excited… after twenty years we’re going to get a new hardiness zone map... This great… Perhaps I can grow more plants than I thought… etc etc…

(Sorry, I'm a bit lost for images considering the map's not actually out yet...)

Sunny weekend of plants in Maryland

Color themed display at Homestead Gardens I’m just back from lecturing at one of the best known garden centers in the east, Homestead Gardens in Davidsonville, Maryland… about 25 miles from Washington, DC. It was the second weekend of their Kaleidoscope of Color spring show and their landscape department had designed some colorful show gardens – featuring marigolds in full flower… in March! They also had an exceptional bargain – large pots of pretty yellow kalanchoe in full flower – for only $1.99.

After a soggy session the previous weekend the sun blazed, the place was packed and carts were filling up quickly as people shopped for plants then dashed home to get everything planted before yesterday’s downpour.

I talked about the many varieties of New Perennials coming on to the market from around the world and, judging by the underlining and scribbled notes on people’s handouts, the staff at Homestead are going to be asked for lots of new plants this season. Especially the many new hellebores, Double hellebores,Terra Nova Nurseries. Image ©Terra Nova Nurseries judging by the number of dropping jaws  when the pictures came on the screen.

Then as I wandered amongst the benches packed with lush perennials after Saturday’s presentation a couple of people stopped to ask me about the new hybrid coneflowers I’d shown – they said they’d been great the first year in the flower gardens, but never came up the following spring.

Drainage is the answer – these new echinaceas hate soggy soil in winter. Consistently moist soil in summer helps them flower for longer and helps prevent the lower leaves from drying up but wet soil in winter is a killer. So choose a sunny, well-drained site. Often the soil in borders becomes raised up over the years with Echinaceas,Terra Nova Nurseries. Image ©Terra Nova Nurseries regular mulching and often that extra depth of soil is enough to allows surplus moisture to drain away from the crowns of the coneflowers. Or choose a site where the soil is naturally well-drained, or amend the soil to improve the drainage.

Also speaking this weekend at Homestead Gardens was Katy Moss Warner – President Emeritus of the American Horticultural Society, no less. You can read about her presentation on the Homestead Gardens blog.

Now, it’s catching up time. When the internet connection in the hotel - the Marriott Courtyard, Annapolis, Maryland… take note - is so slow that it’s almost impossible even to get a Tweet out, I now find I have quite a backlog. OK... on to the next thing – which would be another mug of coffee. After yesterday’s six and half hour drive back through torrential downpours I still need waking up.

Another fake plant picture

GeraniumDoubleJewelVM OK folks, another catalog picture horror for you. My wife judy tells me that bashing on about faked up plant pictures in catalogs is getting tiresome. I don’t agree, but in the spirit of marital harmony I’ll just feature the sillier of the two I had planned for today (here’s the other). This is from the latest UK catalogue from van Meuwen.

But first let me say that just because the pictures are misleading, it doesn’t mean the plants are rubbish, it doesn’t mean that perfectly natural images couldn’t show what good plants they are. This is a good plant - just don’t expect it to grow like this.

Geranium ‘Double Jewel’ (click the image to enlarge) is a lovely double flowered form of the meadow cranesbill, Geranium pratense. It’s a little shorter than most forms of this species, which can reach 4ft/1.2m in height, but here the crown of the plant should probably be below the bottom of this pot – if they weren’t cut stems. It will look great in the garden – but it will never ever look like this.

This is a lovely plant, but can’t we just have a picture of it looking great in a border?

You can order plants of Geranium ‘Double Jewel’ from van Meuwen.

How do you know if a plant is hardy?

I’ve been thinking the muddled issue of hardiness zones this week – and muddled they are indeed. These are ratings that classify plants according to the climatic conditions they’ll tolerate – in particular, how much winter cold they’ll take. Maps divide the world zones according to the prevailing conditions.

UK-ZoneMap American gardeners use them all the time, and for their interest here’s a map of Britain (click to enlarge) split up according to the USDA system widely used in the USA. British gardeners will find the, of course, far more complicated US map below.

The problem is this: At a time when plants (and sometimes their coloured labels) move around the world so quickly, when most plant and garden books are published internationally and with everyone looking up plants online wouldn’t it be more helpful to have one single system?

Britain The RHS has a four zone system (some use an extra zone for parts of Scotland) based not on minimum temperatures but on the growing conditions plants require. The RHS also often cites the actual temperatures plants will tolerate or uses a system of symbols.
Europe Here the USDA system is sometimes used but the European Garden Flora uses its own seven zone system based mainly on minimum winter temperatures.
United States There are three systems. The USDA (United States Department of Agriculture) system of eleven winter hardiness zones and the similar National Arbor Day Foundation system are based on minimum winter temperatures. There’s also the completely different 45 zone Sunset system, used almost Usda_map entirely in the west, that also takes summer heat and other factors into account.
Canada Agriculture Canada has created an eight zone system based on minimum winter temperatures, summer rainfall, snow cover and other factors.Australia Here they use a modified version of the USDA system.

I could go on…

So I’m wondering – does it matter? Well, you know what I think. I write online and my books are published all over the place – it would be simple to use just one system.

What do you think? One system for everyone or each to their own? Keep in mind that any system is only going to provide a rough guide.

Lectures and book signing

A little flurry of events coming up...

20 March (USA)
Kaleidoscope of Color Garden Show
Homestead Gardens, Davidsonville, MD
12pm New Perennials - lecture
I’ll be presenting my look at new (and one or two undiscovered) perennials.
Also featuring at the show: Katy Moss Warner, President Emeritus of the American Horticultural Society

20 March (USA)
The Orchid Show
New York Botanical Garden (latest updated details)
My wife judywhite will be signing copies of her new book, Bloom-Again Orchids and demonstrating orchid care
2.00-3.30 pm Book signing, Q&A and potting demonstration in the Shop in the Garden
3.30-4.30pm Repotting orchids demonstration, Q&A  and book signing in the Green School outside the Enid Haupt Conservatory alongside The Orchid Show. judywhite will be appearing in conjunction with the NYBG's Annual Orchid Show.

21 March (USA)
Kaleidoscope of Color Garden Show
Homestead Gardens, Davidsonville, MD
3.15pm New Perennials lecture
A second chance to see my presentation on new (and one or two undiscovered) perennials
Also featuring at the show: Katy Moss Warner, President Emeritus of the American Horticultural Society

April 16 (UK)
Hardy Plant Society (Staffordshire Group)
Little Haywood Village Hall, Little Haywood, Stafford,
7.30pm Hellebores and Friends - lecture
I’ll be talking about and showing hellebores old and new and plants to grow with them in the garden.

Like to book us to speak at your event? Email Graham or email judy.

Note to burglars: Yes, we’re both away for the weekend of 20/21 March – but you won’t want to mess with our cat sitters! And the cats can give you a nasty glare - so be warned.

Japanese barberry - on the march

Berberisthunbergii10204 I looked out of the window yesterday and discovered why Berberis thunbergii, the Japanese barberry, is turning up all over the place across the woods here in Pennsylvania, and elsewhere. In some areas it’s a menace.

I was just putting some washing in the machine, and I looked thoughtlessly out of the window at the strip of Japanese barberry we have growing along the path at the side of the house and there they were – a dozen or more robins (American robins, that is - check out the very different British and American robins) stuffing themselves on the barberry berries which had held right through this snowy winter till this week.

Five minutes later they were all gone, the birds and almost all the berries – and that’s the point. As the robins move on through the woods, the seeds in their droppings fall as they go. The acid in their digestive system will have primed the seeds to germinate, and germinate they will. And they’ll start to dominate the understory in our forests. BerberisthunberiiForest18124

I’ve kept that one row of barberries, just so I can see how much they spread nearby: hardly at all, in fact. But apart from the occasional chipmunk clambering up the stems I’ve rarely seen anything actually eat the berries. Until now. And it only takes one little flock, on one day… and the Japanese barberries are everywhere. This picture was taken just six or seven miles away (right, click to enlarge).

BUT!! Let’s just be clear: if the numbers of deer in the forest had not risen to such an overabundance and if they hadn’t plundered the native flora so catastrophically then the Japanese barberries (which the deer never seem to eat) wouldn’t have had it so easy.

We've had the tree guy in

Pileated woodpecker,birch,betula,damage, Image: © Do not reproduce without permission. Since the last snow fell - what, about a week ago - someone's been doing a job on one of our birches.

I saw this in the distance across in the woods and couldn't quite see what was going on (click to enlarge). So I went to investigate (trudging through a foot of snow - where are those snowshoes?)

To be honest, we like to leave the dead trees in place for exactly this reason. The grubs Pileated woodpecker munch their way through the dead wood and the pileated woodpecker, (right, click to enlarge) all 18in/45in of him or her, chips away at the wood to munch on the grubs.

But that's big pile of chips to create in just a few days. They come to the bird feeders sometimes, and it's a treat to see them, they're just so huge! And they can do an elegant flute-like job on some trees.

Oh! And a red-tailed hawk just flew by my window and sat on a branch... Not a squirrel in sight, needless to say. They're probably all quivering in the woodpile.

Spring... at last...?

Hamamelis intermedia Pallida mollis, Image: © Do not reproduce without permission. And about time too – we have some flowers.

Quite a lot of flowers, actually – but all on the one plant. While the hellebores and snowdrops are still under a foot or more of snow, the hamamelis is in full flower. So it must be spring. But not another flower in sight.

And this morning we had a red-winged blackbird on the feeder. “It’s a sure sign of spring when the red-winged blackbird returns to the marshes,” says the book (Birds of Pennsylvania Field Guide). Well, tough on the poor blackbird. The marshes are still frozen solid.

Actually, I’m worried about that hamamelis – Hamamelis x intermedia ‘Pallida’. It seems to me that the petals are little bit short, and not quite pallid enough – and it doesn’t really have as much scent as I remember. “Hamamelis x intermedia ‘Pallida’ probably has the strongest scent” says last year’s blog post from RHS Rosemoor. Not this one, it doesn't.

Well, if you must buy shrubs in a sale…

And I wonder what's going on under all that snow? It's basically melting from the underneath so the soil must be warm enough not only to melt snow but encourage a little growth... I'm intrigued.

Great advice on macro photography - from the expert

ALD_080311-002 Macro photography wizard Alan Detrick, author of Macro Photography for Gardeners and Nature Lovers, now has a series of podcasts available from his publisher, Timber Press, in which he reveals how to take great close-up images.

He discusses techniques and equipment and ways to think about macro photography in the accessible way that he’s developed in years of teaching photography workshops.

Well worth a listen, it comes in six parts. Just click to listen.

Alan Detrick’s macro photography podcast – part one

Alan Detrick’s macro photography podcast – part two

Alan Detrick’s macro photography podcast – part three

Alan Detrick’s macro photography podcast – part four

Alan Detrick’s macro photography podcast – part five

Alan Detrick’s macro photography podcast – part six

And check out Alan's fascinating blog, which is packed with good advice, plus the gorgeous macro images on his website.

And be sure to enter the Timber Press drawing to win one of Alan's pictures.

And of course you can order the book.

In North America order Macro Photography for Gardeners and Nature Lovers from

In Britain order Macro Photography for Gardeners and Nature Lovers from

Botanical thrills

VivannoSmoothie The Journal of the Botanical Society of the British Isles (BSBI) arrives. Always intriguing. This issue features, apart from the arcane (but valuable) botanical stuff like eight pages on the identification of two hybrid Juncus (rush) species, something much more exciting.

At their Annual General Meeting in June there’ll be a demonstration of “DNA extraction from a fruit smoothie – using only household reagents”! Sounds great. Actually, it turns out that this is not a unique idea but still – impressive, I’d say. All we need now is advice on how to determine the cultivar of strawberry in the smoothie using tools found in the average suburban garage.

But there are two other valuable features of this issue. One is the list of new plant records for the British Isles – ten and a half pages of them, six pages of which are records of newly introduced species. [For US readers, Berberisdarwinii3949 the area of the British Isles is about the same as that of Michigan, the 11th largest state.] It’s invaluable that discoveries of individual species, sometimes just single plants like the Berberis darwinii found on Sark in the Channel Islands, are recorded as this vital information is crucial to our understanding of the spread (or more often the lack if it) on non-native species. News of similar, state-by-state, records in the US would be appreciated.

Finally, there’s a ten page paper from Michael Braithwaite, President of the BSBI, on how successfully the BSBI has recorded the spread of non-native plants. I may well come back to this important piece another time but one thing jumps out: when referring to non-native plants he encourages us not to use the term “alien” but instead to call these plants “incomers… to avoid being judgmental.”

Here in the US, the term “alien” is routinely used - sometimes, I have to say, with the intention of being judgmental.