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June 2013

A new colour in a thuggish perennial

Pentaglottis sempervirens (Green Alkanet) in its usual blue, and a new form. Image © GardenPhotos.comGreen alkanet, Pentaglottis sempervirens, is robust evergreen perennial in the borage family (left, click to enlarge). “Robust” is perhaps being kind; frankly, it can be a bit of thug. But in wilder parts of the garden in poor soil it can be very useful, squeezing out less attractive thugs like ground elder. It carries its pretty bright blue flowers on 2-3ft/60-90cm stems above rough and rather bristly green leaves.

Green alkanet originates in south west Europe, was first grown in British gardens in 1700 but had already spread into the wild by 1724. It has since spread over much of England and Wales, but is seen less often in Scotland and Ireland.

It is also found in along the American west coast from California to British Columbia as well as in Maine; in North America it’s as often known as evergreen bugloss. I’m surprised it’s not established itself more widely… and more notoriously.

I’ve been fortunate enough to find plants with flowers in two other colours in addition to the usual bright blue, the latest just a couple of days ago. I’d parked the car in a car park near a large demolition site just a few miles from the RHS Garden at Wisley, just south of London (in the village where the former singer and guitarist from The Jam, Paul Weller, lives as it happens). I got out of the car to go to the post office to post a card to my lovely wife back home in Pennsylvania and I spotted the plant you see in the picture – instead of bright blue flowers, the flowers are white with a ring of blue flashes around the centre. Lovely. But not the time of year to dig it up, unfortunately.

Decades ago I found a form with lovely pale blue flowers, which the owner of the garden where I spotted it called ‘Morley China Blue’; it was available from a nursery for a year or two, but has now vanished.

And about as long ago, photographer and plant breeder John Fielding found a stable variegated version which never self sowed so was very well behaved. He passed it to a large nursery for propagation – and they lost it.

The point of all this, I suppose, is to make the point that even amongst the most familiar (and not universally admired) plants, are interesting and attractive new forms. We just have to keep our eyes open.

UPDATE: Went back yesterday for another look - someone's been in with the weed whacker, just a pile of dried up stems is left. And the marker I'd left so I could go back and dig up the plant in the autumn has gone too...

Choosing the best delphinums

Delphinium-Red-Caroline-17206Back in the spring, I posted here about the generally poor quality of delphiniums raised from seed and how Terry Dowdeswell’s New Millennium delphiniums were really the only top quality option.

But, of course, the traditional way to propagate the best named delphiniums is from cuttings, that was the method used for so many of the fine plants seen towering at the back of traditional British herbaceous borders over the years. The problem is that individual delphinium plants produce so few cuttings that, again, they can be expensive to buy a nd uneconomical for nurseries to produce.

But now there is another form of vegetative propagation that will guarantee top quality: tissue culture. Plants in the buttercup family (Ranunculaceae) have been famously tricky to propagate in the laboratory by tissue culture but now Clematis are routinely produced in this way, along with some hellebores, mainly hybrids of H. niger. There has not been success with Aquilegia, Hepatica or Ranunculus but a few - just a few - delphiniums have yielded to this technique.

The first of the Elatum Hybrids to be tissue-cultured were the pink-flowered cultivars, the University Hybrids, developed in a long-running breeding program by Professor Legrow, and concluded at the RHS Garden at Wisley. The first, Princess Caroline (‘Odabar’), was launched at the 1994 Chelsea Flower Show and, although a poor garden plant, its availability through tissue culture led to its widespread use as a cut flower. It was followed by ‘Red Caroline’(above, click to enlarge), ‘Red Rocket’ and ‘Coral Sunset’.

Much more recently the Highlander Series has become available. Developed in Scotland by Tony Oakley, this is a new series of five cultivars with a superficial similarity to one of my favorite of all perennials, ‘Alice Artindale’. Each sterile flower is fully double, with about fifty slender petals creating a flower like a frilly button. The flowers are carried in spikes of about thirty or more and five cultivars are currently available: ‘Blueberry Pie’ (deep lilac with a green center), ‘Crystal Delight’ (a very frilly pale lilac with a yellow-green center - right), ‘Moon Light’ (pale lilac bordered in blue with green center), ‘Morning Sunrise’ (white with a green Delphinium-CrystalDelight5-cc11center), and ‘Sweet Sensation’ (deep mauve-purple, tinged with blue-green). Without tissue culture they would be almost impossible to buy.

So, as we think about buying delphiniums, we must choose: pay the proper price for a really good plant, or buy a second rate plant for a cheap price. There’s only one answer, really. One really good plant is worth any number of second rate ones and now, with tissue culture, good plants are becoming easier to buy.

In the UK, a wide range of superb award-winning cuttings-raised delphinium cultivars is available in limited numbers from  Larkspur Nursery  Plants of the Highlander Series are available from Hayloft Plants and elsewhere; Princess Caroline (‘Odabar’) and ‘Red Caroline’ are available Burncoose Nurseries. In North America, even tissue-cultured delphiniums are very hard to find although ‘Crystal Delight’ (Highlander Series) and ‘Coral Sunset’ are available mail order from Hirts. There are clearly some great opportunities for mail order retailers.

* This is the second part of a piece entitled Buying Good Delphiniums which appears in the current issue of the Newsletter of the Ranunculaceae Group of the Hardy Plant Society. Anyone with an interest in hardy plants in the Buttercup Family (Ranunculaceae) should join. The first part was posted here in April.

 

 



Native or non-native: which plants are best for insects?

Shrubby hare’s ear, Bupleurum fruticosum, is a top plant for hoverflies (André Karwath aka Aka (Own work) ‘CC-BY-SA-2.5 (www.creativecommons.org/licenses/by-sa/2.5)’, via Wikimedia Commons)
When, a couple of years ago, I wrote about non-native plants often being better for wildlife than native plants it prompted a lot of comments, for and against, and also private emails – mostly against, including some that were unexpectedly unpleasant.

Undeterred, I bring news of an article by Dr Ken Thompson in Britain’s Which? Gardening magazine, published by the impartial, non-profit Consumers’ Association (similar to Consumer Reports in the US) which says the same thing: “Recent research shows that non-native plants can be just as attractive to wildlife as native ones – if not more so.”

Ken Thompson, of the University of Sheffield, is a biologist with a special interest in the science of gardening. He’s examined recent research at the Social Insects Lab at the University of Sussex, and at the Royal Horticultural Society’s Plants for Bugs project and reports that “pollinating insects have no clear preference for the flowers of native plants”.

So we gardeners can rest easy. If we’re looking to attract insects and other wildlife to our gardens, garden plants are often better than native plants. And there seems to be no argument that, especially in densely populated areas, gardens make crucial contributions to the success of so many birds and insects

Borage, Borago officinalis, is the ultimate honeybee plant. Image So what to grow? To attract pollinators, Ken Thompson recommends these four plants:
Borage - “The ultimate honeybee plant” (left, click to enlarge)
Buddleia – “For butterflies, you still can’t beat buddleia, which is also used as a larval food plant by at least 19 different moths”. [Note: Buddleia is invasive in some parts of the USA, where only varieties that do not produce seed should be planted.]
Catmint – For bumblebees “for sheer attractiveness over a very long flowering season”
Shrubby hare’s ear (Bupleurum fruticosum) – For hoverflies, “a plant you’ve almost certainly never heard of”. (top)

So these are the first plants to try. And the number of hoverflies you’ll find on that bupleurum is amazing.

Ken Thompson’s article Native vs non-native plants: which are best for wildlife? appears in the June 2013 issue of Which? Gardening magazine. It is not available online.

You can subscribe to Which? Gardening here

You can check out books by Ken Thompson on amazon.co.uk

You can check out books by Ken Thompson on amazon.com