Perennials

Transatlantic plant trials - any value?

Phlox and Sweet Pea Trials at the Royal Horticultural Society's garden at Wisley, near London. Image ©GardenPhotos.com
On both sides of the Atlantic, independent trials of perennials are organized by a number of different organizations. But I’ve sometimes seen the Royal Horticultural Society’s Award of Garden Merit (AGM), often given after trial (phlox and sweet pea trial, above), used in American catalogs and wondered how much relevance this British award has in North America. And does the Plant Evaluation Program run by the Chicago Botanic Garden and, in Delaware, the trials run by the Mount Cuba Center (baptisia trial, below) have any relevance in Britain?

Well, this year I’m chairing a group of experts working to update the list of AGM heucheras for the Royal Horticultural Society (RHS) and I’ve sent all the participants copies of the reports of the heuchera trials at both Mt. Cuba and the Chicago BG.

Of course, the climate in Delaware and in Illinois is, well, rather different from the climate in Britain but, for hardy perennials, if they grow in Delaware or Illinois, they’ll generally grow in Britain. And while modern American heuchera breeding is often focused on suitability for specific climates, the way the plants look when they’re growing well is relatively constant; a harmonious combination of flowers and foliage works well in any climate. So these reports will provide valuable background to our deliberations.

At first I was skeptical, but now I can understand why the AGM appears in American catalogs – it’s one of a number of useful factors that inform choice. The problem is that some gardeners in Texas or Maine, while they may see that the plants look wonderful, may not appreciate that the plants are given their award in a climate that’s closer to that of Oregon or Washington state may not do well for them. In fact they may die their first year.

But it’s not just climate, there’s another thing going on. I suspect that most British gardeners, seeing trial results from Delaware or Illinois, will just assume that they’re of no relevance, or even interest, and ignore them. True, disease resistance in American trials is unlikely to be of value elsewhere as different forms of the same disease are found in different places. But if the flowers are a dingy color in Chicago they’ll be dingy in Britain, too

American gardeners, on the other hand, seem to have a more open attitude and although they may not want to read the detailed reports of the RHS trials in which plants were given the AGM, they’re happy to accept that this is useful information and allow the awards to inform their plant choices as they decide what’s right for their own gardens.

And perhaps, as the dissemination of information about plants becomes more global, these reports help writers and advisors and consultants develop a deeper understanding of the plants so that the guidance we pass on is more informed. And they help nurseries decide what to grow. These trials and their reports are certainly invaluable to me. Even something as simple as paying attention to the factors these reports consider important is useful.

* The Mount Cuba Center is based near Wilmington, Delaware, just over an hour north of Washington DC, and its primary aim is to foster enthusiasm for native plants and their conservation. You can download their trials reports here.

* The Chicago Botanic Garden has been organizing trials of hardy perennials, and other plants, since 1985 under the expert guiding hand of Richard G. Hawke. You can download their trials reports here.

* The Royal Horticultural Society has been running trials of everything from hamamelis to cabbages to marigolds since, it seems, time began. You can search their database of trials here.
Baptisia trial at the Mount Cuba Center. Image ©Mount Cuba Center.


Plants For 2017: Perennials for 2017

Finally, in this week of daily postings on the best of 2016 and looking ahead to 2017, two exciting perennials to look out for in the year ahead.

Hosta 'Branching Out'. Image ©Plant Delights
Hosta
‘Branching Out’

Tony Avent at Plant Delights in North Carolina started out to create a hosta with branching flowering stems back in 1989 and, usig five different parents and after a number of generations of crossing and selection, ‘Branching Out’ is the result. (You can read more on Tony’s blog.)

Its pale lavender flowers on their sturdy 30in/90cm branching stems make an attractive and prolific show in mid summer over broad, heavily veined, dark green leaves. All we need now is added fragrance.

Hosta ‘Branching Out’ is available in North America from Plant Delights, it is not yet available in Britain.


Ajuga reptans 'Choc Ice'. Image ©Monksilver NurseryAjuga reptans 'Choc Ice'
There are few plants with bronze or purple foliage and white flowers. It’s a matter of genetics, the bronze or purple leaf colouring tends come with flowers colours at the same end of the spectrum. Astilbe ‘Chocolate Shogun’ is close, its chocolaty purple leaves topped with pale pink plumes.

And here’s another candidate, a bugle with white flowers held above purple leaves and bracts. OK, it all turns greener late in the season but at flowering season, it looks impressive. Discovered by plantsman Geoff Hitchens.

Ajuga reptans 'Choc Ice' will be available again soon in Britain from Monksilver Nursery. It is not yet available in North America.



Plants Of The Year 5: Cool new primula

PrimulavialiiAlisonHolland-900
Ending the first part of my daily review of the some of the most memorable plants, new and old, from last year we come to the 2016 Chelsea Flower Show favorite – the new white flowered form of Primula vialii .

Primula vialii 'Alison Holland’
As soon as I entered the showground on the Sunday morning before the show opened on the Tuesday, plantspeople were asking me: “Have you seen the new white primula?” So off I rushed to take a look – and it’s lovely. I wrote it up on my RHS New Plants blog back in June. It was shortlisted for the 2016 Chelsea Plant of The Year award.

Basically, instead of the red buds and lilac flowers of the wild Primula vialii from China, ‘Alison Holland’ has creamy green buds and cool white flowers. Gary McDermott of Harperley Hall Farm Nurseries, who introduced the plant at Chelsea, told me that it’s more vigorous and flowers for longer than the usual form. But it hates drought.

‘Alison Holland’ was found in 2011 in his garden in the north east of England by John Holland who named it for his daughter-in-law. Plants never set seed but this form has proved easy to propagate by tissue culture.
 
Primula vialii 'Alison Holland' is available in the UK from Harperley Hall Farm Nurseries.

Primula vialii 'Alison Holland' is not yet available in North America but should be soon.


Plants Of The Year 3: Unique foliage perennial

HeucherellaSolarEclipse
Continuing with the third of seven daily posts about the plants that caught my eye last year, we come to a fine perennial that I noted thriving in a number of different situations.

xHeucherella ‘Solar Eclipse’
With so many heucherellas on the market, its important to take a deep breath before pronouncing one as “unique” – but here goes: xHeucherella ‘Solar Eclipse’ is unique.

This distinctive clump-forming variety has slightly ruffled, prettily scalloped, reddish brown, almost chocolate brown, leaves with a neat minty green margin. It keeps its color well and matures into a clump about 20cm high and 40cm wide. The flowers are white – but not really the point. The cut leaves last quite well in water, too.

Lovely in a terracotta pot, it also looked unexpectedly good in a blue pot and at the front of border in dappled shade. In cool areas with water retentive soil it will grow happily in full sun but is general happier in some shade.

‘Solar Eclipse’ is sport of ‘Solar Power’ (which has yellow leaves with a red central pattern) and was developed by Janet Egger and Chuck Pavlich at specialist perennial breeders Terra Nova Nurseries in Oregon.

xHeucherella ‘Solar Eclipse’ is currently available retail in the UK from these Royal Horticultural Society Plant Finder nurseries.

xHeucherella ‘Solar Eclipse’ is currently available retail in North America from many suppliers including Bluestone Perennials and Plant Delights.


The day our echinaceas died

Echinacea 'Flame Thrower' © Terra Nova Nurseries
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.

Double echinaceas from Marco van Noort. ©Luc Klinkhamer


Most Christmas roses used to be pink!

HelleborusGiant-TheGarden-1878
“The Christmas Roses with which one meets in the majority of gardens are not white, but pink, or more or less suffused with pink or dirty purple.”

Really? Well, perhaps it was true in 1878 when a certain Mr. D. T. Fish wrote those words in William Robinson’s epic journal, The Garden, although it seems unlikely. He then goes on to explain in detail how to make Christmas roses (Helleborus niger) white.

Even allowing for the artist’s overenthusiasm, this Giant Christmas Rose, illustrated in The Garden in 1878 (above), is impressive and well illustrates how the coloring works: individual flowers open white and develop pink tones and become richer in color as HelleborusLouisCobbett700they mature. Sunset Group, collected in Slovenia by veteran British hellebore expert Will McLewin was similar (but a whole lot less dramatic). Dark stemmed ‘Louise Cobbett’ opens with pink backs to its flowers and later develops additional pink tints but it’s not the color of the Giant Christmas Rose.

Neither is Blackthorn Group (below), developed by acclaimed hellebore and daphne breeder Robin White from ‘Louise Cobbett’ (right) and ‘White Magic’ although it’s a lovely thing.

Strangely, Josef Heuger, in Germany, who has introduced so many fine forms of the Christmas rose recently - ‘Jacob’ flowers dependably in November here in Pennsylvania - has created no pinks. Most of the pink ones such as ‘Pink Frost’ which listed as H. niger by mail order nurseries are actually hybrids. If Ernie and Marietta O’Byrne of Northwest Garden Nursery in Oregon, who’ve created so many spectacular double and single forms of H. x hybridus, turned their attention to Christmas roses we’d be in for a treat.

Anyway, it’s interesting (if difficult to believe) that pink was once normal in Christmas roses and that detailed suggestions were given in The Garden for turning them white.  And what, in short, were the recommendations: “light soil”, “a warm, sheltered, partly-shaded situation” and “cover them with glass”. Somehow that doesn’t really seem a very convincing way to change their color…

HelleborusBlackthorn2143


Not yet winter in Pennsylvania

Geranium phaeum 'Samobor' seedling with startling fall leaf color. Image ©GardenPhotos.com
National Public Radio reported this week that lilacs were in bloom in Washington, DC. A friend near here in Pennsylvania reports picking salad leaves from the open garden just a few days ago while anther says her spring crocuses are in bloom. It’s been mild back in Britain too.

Here in our garden the mild season has ensured that some plants developing late fall color have lasted and lasted. One young seedling of Geranium phaeum ‘Samobor’ has produced some spectacular leaves (above, click to enlarge); the original plant and other seedlings are more of a blotchy yellow.

Hydrangea-quercifolia-Little-Honey-_J037665-700One of my favorite shrubs, Hydrangea Little Honey (‘Brihon’) (right, click to enlarge), a dwarf yellow-leaved form of the oak-leaved hydrangea, always turns burgundy red in the fall but often a couple of sharp frosts reduces the plant to bare stems. Not this year, the leaves have been wine red for weeks with a few just starting to develop fierier tones as they prepare to drop.

The other effect of these unseasonably mild weeks has been that after the first few, relatively gentle, frosts turned everything in the riverside meadows tawny brown – that’s how they stayed. The foxtail grass in the fields where the rudbeckias are such summer stars, I think this is Setaria viridis, has neither been crippled by frost nor battered by rain or snow and still stands out against the leafless escarpment. Lovely.

We’ve gentle frosts forecast for the weekend, with a high of 57F and a low of 39F forecast for Christmas Day. The snowdrops are in bud, but check out the Snowdrops In American Gardens Facebook group for news of plenty of snowdrops blooming merrily all over the country.

Oh, and a friend in Downeast Maine reports that the grass is growing and needs a trim. But I don’t care how long it gets here we’re not cutting the grass in December.

Foxtail grass, Setaria, still looking lovely on the Delaware River flood plain. Image ©GardenPhotos.com


New varieties of the easy and elegant primula

746_primula_flamenco-1000x750_0
In recent years, Barnhaven Primroses, originally from Oregon and now in France (via England) have been branching out. Nothing dramatic, but alongside primroses they’ve been expanding their choice of other primulas and also added hellebores to their range.

One exceptional, and much underrated, plant they’ve been championing is Primula sieboldii and they’ve recently announced the availability of some lovely forms from Japan, including the double-flowered ‘Flamenco’ (above). They’ve been quietly been building up stock for some time.

This is an exceptional species, with fresh looking, bright, divided leaves and a flurry of up to ten spring flowers held on upright stems. Sound like a polyanthus? Yes, but so much more delicate and stylish.

In the wild, it’s a woodlander creeping through wet woods in Japan, Korea, China, Russia and, as the canopy closes, the foliage fades away. In summer I find it will take drought, although it’s worth remembering that the plants dislike lime. And it’s very hardy: USDA Z4, RHS H7.

The only problem is that with no sign of it above ground from late summer until mid or late spring, it’s easy to forget precisely where you planted it and attempt to plant something else in its space.

Our plants here in Pennsylvania came from the late and much lamented Seneca Hill Nursery in upstate NY and I always pick a few stems to bring indoors from the expanding clumps. Some of the clumps have expanded so much that they’ve escaped the borders, meandered under the boards supporting the raised bed and emerged on the path.

764-sieboldii-Trade-Winds-1000x750_0Lazy’s Farm now seems to have the best choice in the US but, in Europe, always start at Barnhaven. They have seventeen varieties of their own raising, including ‘Trade Winds’ (right, click to enlarge) and twelve Japanese varieties available as plants, including the lovely ‘Flamenco’ (top) and some delightful forms with white picotee edges to the flowers. Nine more varieties are available as seed. 

Barnhaven will send seeds, and also plants, to the US, with a phytosanitary certificate at a cost of 11.43 euros. If customers have a small seed lots permit there is no phyto charge for sending seeds. [After six months I'm still waiting for my small seed lots permit...]

Perhaps people are disconcerted by the fact that the plants disappear for much of the year, or perhaps the intolerance of too much lime puts people off. But considering how easy they are to grow, we really don’t see them enough. They’re much easier to keep over the long term than the special varieties of primroses and polyanthus which so often seem to fade away after a few years.

In Japan, the heyday of Primula sieboldii was from the beginning of the 17th century to the mid 19th century but now Barnhaven and others are re-inventing them after so many varieties have been lost over the centuries. And it’s not as if they need careful cossetting and conditions it’s tough to provide. They’re easy… give them a go.


New heuchera that's quietly different

Heuchera 'Berry Timeless' is a container in partial shade. Image © GardenPhotos.comIn the first waves of enthusiasm for heucheras, back in the 1930s and then the 1950s, it was the flowers that were key and in fact many varieties were developed specifically as commercial cut flowers.

More recently, of course, foliage has been the thing and an astonishing range of foliage colors and patterns has been developed although many have poor flowers which are best snipped away.

So, obviously, the next thing was to bring the two features together. ‘Rave On’ is pretty good in combining good foliage with good flowers, but flowering tails off as spring passes. But, so far, ‘Berry Timeless’ (left, click to enlarge) really does look the part - even if the name is a bit corny.

OK, this is its first season on trial here but it’s clear that its bright silver foliage with minty green veins makes a lovely low dense mound. The flowers open in pale pink and fade to richer tones and, unlike the flowers many heucheras, they don’t fall off. Even while the little green seed capsules are developing the dusky reddish pink flowers are still colorful.

Old and new flowers on Heuchera 'Berry Timeless'. Image © GardenPhotos.comIt’s now August and there’s plenty of old flowers, new flowers and buds still on the plants (right, click to enlarge). And there’s another thing about the flowers: the length of bare stem below the flowers is relatively short so the flowers sit just above the leaves without a long length of bare stem in between. That’s a feature that really improves the look of the plant.

Developed by Walters Gardens in Michigan rather than the heuchera hatchery that is Terra Nova Nurseries, where most new heucheras originate; look out for more from them in the future.

Heuchera ‘Berry Timeless' is available in Canada from Canning Perennials and in the USA from Garden Crossings. It’s not yet available in Britain, but should be soon.


Slug resistant hostas?

Slug resistant hostas? Yes, well, maybe…

Slug resistant(!) Hosta 'Brother Ronald' destroyed by slugs. mage ©GardenPhotos.com

Anyone who writes anything about hostas usually ends up saying that some varieties are slug resistant. But let’s stop right there: what do we mean by “resistant”? Well, we don’t mean immune, that’s for sure. What we mean is that they’re far less likely to be eaten than other hostas, that’s all.

These are varieties that have unusually thick and heavily textured leaves that the slugs struggle to munch through. They’re often related to the old favorite H. sieboldiana ‘Elegans’ and many of them have blue foliage.

Now, I was looking for a hosta for my daughter Lizzie’s small town garden recently. And slugs are definitely a problem. So, I took a look at the huge range on sale at the Plant Centre at the RHS garden at Wisley near London and picked out one I didn't know, ‘Brother Ronald’. The foliage is really tough and leathery, it’s a lovely puckered blue color and it doesn’t get too big. Ideal.

It turned out that it was raised by Britain’s only notable hosta breeder, Eric Smith, who also raised ‘Halcyon’, ‘Hadspen Blue’ and others that often hold their own against slugs. What’s more, I discovered that hosta wizard Mark Zilis marks it as “slug-resistant” in his superb Hosta Handbook.

Well, a couple of days later I had an email from Lizzie. You can see what happened (above). Too many starving slugs.

Here in Pennsylvania, we have not one slug bite on a hosta this year, in spite of the wet season. – although last night’s roof rattling thunderstorm has punched a few holes in one or two. But of course we have frogs and snakes around to help keep the slugs under control.

Hosta 'Blue Mammoth'- no slug damage. Image ©GardenPhotos.com

‘Blue Mammoth’ (above) is majestic as usual, ‘June’ (below), a sport of another Eric Smith variety, ‘Halcyon’, is also pristine as is ‘Great Expectations’.

Diana Grenfell published a list of ten slug resistant hostas in her excellent book, A Gardeners Guide to Growing Hostas. She recommended: ‘Blue Umbrellas’, ‘Fragrant Gold’, ‘Green Sheen’, H. hypoleuca, ‘Invincible’, ‘Krossa Regal’, ‘Leather Sheen’, H. sieboldiana forms, ‘Silvery Slugproof’ and ‘Sum and Substance’. A good choice.

In my Encyclopedia of Perennials, I included a longer list of slug-resistant hostas that I and Mark Zilis put together. It included most of Diana Grenfell’s list plus: ‘Abiqua Drinking Gourd’, ‘Big Daddy’, ‘Blue Angel’, ‘Blue Dimples’, ‘Blue Mammoth’(above, good with us), ‘Blue Moon’, ‘Blue Wedgewood’, ‘Dorset Blue’, ‘Fragrant Bouquet’, ‘Gold Edger’, ‘Gold Regal’, ‘Great Expectations’ (great for us in PA), ‘Hadspen Blue’, ‘Halcyon’ (good with us), ‘June’ (below, good with us), ‘Love Pat’, ‘Northern Exposure’, ‘Sagae’, ‘Sea Lotus Leaf’, ‘Spilt Milk’, H. tokudama forms and ‘Zounds’.

I wonder if any of these recommended hostas can take the pressure that finished off ‘Brother Ronald’?

Hosta 'June' - no slug damage. Image ©GardenPhotos.com

Order the Gardeners’ Guide to Growing Hostas in North America
.

Order the Gardeners’ Guide to Growing Hostas in Britain.

Order my American Horticultural Society Encyclopedia of Perennials in North America.

Order my Royal Horticultural Society Encyclopedia of Perennials in Britain.

Order The Hosta Handbook by Mark R. Zilis in North America.

Order The Hosta Handbook by Mark R. Zilis in Britain.