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October 2013

September 2013

Four, long season foliage plants

Impatiens omeiana, Hosta 'Maui Buttercups' and Brunnera 'Silver Heart'. Image ©
One of the first plants we bought for our Pennsylvania garden, years ago now, was a hardy Chinese Impatiens species called Impatiens omeiana. It's a hardy perennial related to the colorful Impatiens seen in containers around the world. As you can see (above, click to enlarge), in summer it features these beautifully marked leaves and now we’re seeing clusters of yellow flowers in the tips of the shoots (blow, click to enlarge).

We’re in US hardiness zone 5 (-29C/-20F) which is off the cold end of the scale of the new British hardiness ratings system launched earlier this year by the RHS. The winters certainly get chilly and occasionally our Chinese Impatiens has taken a hard knock. Some years, in spring, just a few spindly shoots emerge but by summer those few stems are looking luxuriant and the following year there’s again a fat clump. This year, we have a couple of interesting perennials underneath, Hosta ‘Maui Buttercups’ and Brunnera ‘Silver Heart’.

Hosta ‘Maui Buttercups’ is one of the best yellow-leaved hostas and it’s also small, not much more than 25cm/10in in height – it’s a classic “sunshine in a shady place” plant and its coloring connects with the stripe in the Impatiens leaf and with its yellow flowers. A cross between two old favorites, 'Frances Williams' and 'August Moon’, the off-white flowers are, frankly, a distraction; I’d snip them off. This is a plant that suffered in our vole infestation but is now thriving again.

Impatiens omeiana with foliage of Ampelopsis brevipedunculata var. aximowiczii 'Elegans'. Image ©GardenPhotos.comAlso tucked under there is the brand new Brunnera ‘Silver Heart’ which is a new improved form of ‘Looking Glass’ with very heavy duty foliage and a brighter silver sheen – it really gleams.

The foliage shape of both these perennials contrasts attractively with the slender Impatiens leaves, and all are happy shaded from the east, and from the west late in the day.

Farther back, the leaves of a climber in a different shape have made their way over from a pot a few feet away. It’s a climber that goes by a rather heavy-handed name – Ampelopsis brevipedunculata var. maximowiczii ‘Elegans’ (left, click to enlarge), or is sometimes known as the variegated porcelain vine. As well as these very pretty variegated leaves, clusters of porcelain blue berries mature in the fall. The green-leaved version of this plant is invasive in some parts of North America, but here this variegated form has never produced a seedling.

But these four plants have made an appealing plant picture for months – and they’re still going strong at the end of September.

North American gardeners
You can order Impatiens omeiana from Burpee
You can order Hosta ‘Maui Buttercups’ from The Hosta Farm
You can order Brunnera ‘Silver Heart’ from Romence Gardens
You can order Ampelopsis brevipedunculata var. maximowiczii ‘Elegans’ from Digging Dog Nursery (though it may be considered invasive in some parts of North America)

British gardeners
You can order Impatiens omeiana from these RHS PlantFinder nurseries
You can order Hosta ‘Maui Buttercups’ from Mickfield Hostas
You can order Brunnera ‘Silver Heart’ from Coblands Nurseries
You can order Ampelopsis brevipedunculata var. maximowiczii ‘Elegans’ from these RHS PlantFinder Nurseries
Impatiens omeiana in flower in September. Image ©

"Don't buy seed of perennials," says British expert!

Achillea 'Summer Berries': easy to raise from seed. Image ©
Which? Gardening is a prestigious British gardening magazine. American readers could think of it as a sort of horticultural version of Consumer Reports. In this month’s issue there’s an article by one of Britain’s top plantspeople and nursery growers, Bob Brown of Cotswold Garden Flowers, about growing perennials from seed.

In it he says: "My experience is that seed of perennials will only reliably germinate if it's sown immediately, certainly within the month. If it gets as far as a packet or a seed catalogue it's already too old." And also... "My advice generally would be not to buy seed of perennials.". Yes, he recommends home gardeners not buy seed of perennial plants. The only exceptions he mentions are "lupins, delphiniums, cactus and other succulents".

Now I have a huge respect for Bob: he’s a fine plantsman, a fine grower and as a judge of the Royal Horticultural Society’s plant trials his insight and unvarnished opinions are invaluable. But, in this case, I’m afraid he’s just plain wrong. The only perennial seeds to buy from catalogues are delphiniums and lupins? I don’t think so. Over the years I’ve raised thousands of perennials from bought seed, fresh seed and seed found in brown paper bags in the back of the shed. Most of it comes up.

It’s a shame that Bob’s recommendation could prevent gardeners from growing a vast range of fine garden plants.

Delphinium 'Guardian Blue': even Bob Brown suggests growing delphiniums from seed. Image ©GardenPhotos.comRichard Oliver, the UK manager of Jelitto Perennial Seeds, whose catalogue lists seed of over 3700 perennials and who’ve been in business for over fifty years, disagrees with Bob: “His comment is frankly wrong. Some of the seed packet stuff may be too old, or more likely, have been stored in really unsuitable conditions, but his comments are otherwise nonsense. For example: Dianthus, Achillea (above, click to enlarge) and Telekia, among others, can germinate over 90% within one week even if stored longer than 10 years. Most of our perennial seed has been tested and has a germination rate of about 70% or more. All the world’s seed banks would be useless if he was right.”

And Derry Watkins agrees. For twenty years she’s run Special Plants in Wiltshire where she not only raises a huge range of perennials from seed but teaches seed-raising techniques to gardeners. Derry told me: “I think he’s mad. Most perennial seed will germinate after 5-10 years if kept cold and dry. It may not be quite so quick or prolific, but you get the plants you want. Fresh is best, but with good storage conditions, old is fine. I sow 2-3 year old seed all the time without a problem.”

Across the Atlantic, the same view prevails. Allen Bush, the Director of Special Projects in the American office of Jelitto Perennial Seeds reminds me: “What to make of 30,000 year old seed of Silene stenophylla? Perennial seed does germinate.” Frozen seed of Silene stenophylla was found in Siberia in 2007 and scientists from the Russian Institute of Cell Biophysics announced last year that they had regenerated plants from seeds carbon dated to 31,800 years old.

I also asked top American grower and plantsman Tony Avent of Plant Delights for his view. “There are certainly some seeds that will not store well, and others that loose viability when they are not stored properly. But most plants in the Asteraceae (daisy) family, for example, won’t even germinate fresh since they require a long after-ripening period.”

So… Sorry Bob, but we don’t agree. In your article you emphasize raising plants from seed collected from our own, and our neighbors’ gardens. Fine. But most commercial seed suppliers know how to store seed correctly, and test it regularly, so that when it’s delivered it’s ready to sow, and ready to grow. OK, some needs special treatment. But advising gardeners not to buy seed of perennials at all cuts them off from an economical way to raise thousands of fine garden plants.
Rudbeckia 'Goldsturm': 99.9% true from seed, and easy. Image ©

The pictures (click each to enlarge):
Achillea 'Summer Berries'
- Mix of fruity colors, easy to raise from seed, germinates quickly.
'Guardian Blue' - One of the best blue delphiniums to raise from seed. Bob excludes delphiniums from his "don't buy seed of perennials" advice.
Rudbeckia fulgida var. sullivantii 'Goldsturm' - 99.9% true to type, easy to raise from seed, germinates quickly.

Unique British sweet pea - also available in the US

Sweet Pea 'Cherub Northern Lights', gorgeous colours on a dwarf plant. Image ©Mark Rowland

The dwarf ‘Cupid’ sweet pea, with white flowers, was first discovered in California in 1893 and, after a flurry of favor, and the addition of other colors, by 1914 interest had faded away.

In the 1950s enthusiasm revived, more colors were selected in the Cupid Series, the semi-tall Jet Set, Knee-Hi and Explorer series were created and more recently Mark Rowland of Owl’s Acre Sweet Peas (who send seed to North America as well as Britain) developed his own improved dwarf series, the Cherub Series.

Now in fourteen colors, ‘Cherub Northern Lights’ is the latest in the series and is unique in dwarf sweet peas. “The flowers open pale with a delicate crimson flare gracing the centre of the standard and a blue picotee edge to the wings,” writes Mark in the 2013 British National Sweet Pea Society Annual where he gives an interesting account of the development of ‘Cherub Northern Lights’. “The colours slowly spread to suffuse the petals and it was this ever changing effect that inspired the choice of name.” Bred from his unique modern Grandiflora sweet pea ‘Fire & Ice’, it brings the subtle colouring and outstanding fragrance of ‘Fire & Ice’ to a dwarf plant. By the end of the season plants form a mound about 30cm/12in high (below).

Sweet Pea 'Cherub Northern Lights' in a hanging basket in the UK in June. Image ©GardenPhtos.comMark’s Cherub Series, launched at the Chelsea Flower Show in 2006, and now available in fourteen colors and a mixture, has proved an excellent series for containers. “To give of their best they need plenty of sunlight, good drainage and plenty of air movement,” Mark says on his website. “This makes them ideal for container growing, and three or four plants in an 45cm/18in tub will give a spectacular display.”

Mark also has the first two varieties in a completely new dwarf series, the Sprite Series, which flowers much earlier than plants in the Cherub Series or Cupid Series. ‘Dark Sprite’ is a maroon and violet bicolor, while ‘Lavender Sprite’ is clear lavender and won an Award of Garden Merit in this year’s Royal Horticultural Society sweet pea trial. I saw it in baskets (left, click to enlarge) and it was lovely. Both reach about 25cm and should be begin to flower in late May in Britain.

Gardeners on both sides of the Atlantic can order these and many other sweet peas from Owl’s Acre Sweet Peas. Dwarf types can be tough to find in North America.

You can read more about sweet peas in my recent piece in Britain's Daily Telegraph newspaper and I’ve brought together news of all the new sweet peas introduced in Britain this season on my Royal Horticultural Society New Plants blog.

The natural spread of Sweet Pea 'Cherub Northern Lights'. Image ©Mark Rowland

Thanks to Mark Rowland for the images at the top and bottom of this piece.

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.

Wasps’ nest over the water

Wasps' Nest hanging from a maple over the water. Image ©

Yesterday evening I took the kayak out round the lake on which our house sits. It’s a little over two miles all round and, after just over half a mile, I noticed something hanging from a waterside maple. I paddled closer. It was this wasps’ nest.

It was more than a foot/30cm+ from top to bottom, it was hanging from a rather slender branch (as you can just see) about 12ft/4m out from the shore and its weight had brought it down perilously close to the water… It was hanging just a few inches above the surface. I suppose when the wasps started building it was 2-3ft/60-90cm above the water – not any more. As it grew larger and heavier it hung lower and lower.

There was a noticeable hole towards the bottom of the nest, on the side facing the shore, and there were large, dark wasps going in and out. I’d have liked to take a closer look but, to be honest, I didn’t want to get too near. And the wind kept blowing me towards it.. But I wanted to take a picture…

My knowledge of the behavior of wasps is largely derived from TV cartoons so I knew that if I got too close they’d all come streaming out of the nest and chase me across the lake as I paddled frantically to get away until I jumped in the water – at which point they’d all laugh and head back home. So I soon paddled away.

Still, it was a great thing to see – even if it may only take one thunderstorm to raise the water level and ruin their nest. And thunderstorms are forecast today.

UPDATE: Two weeks later I paddled over and took another look - someone's smashed up the nest. What's the point of that?