Ivy is a plant that divides opinions. Attractive foliage, good for wildlife, cools buildings… Invasive, ruins walls, harbours pests…. Research and opinion on all these issues has been in the news increasingly in recent years and now the most comprehensive book on ivies ever produced has been published by The Royal Horticultural Society.

Hedera: The Complete Guide by Hugh McAllister and Rosalyn Marshall is exactly that – the complete guide. With more than four hundred pages, and impressively illustrated in colour throughout, this is the second in the RHS Horticultural Monograph series which began with last year’s excellent book on kniphofias.

This is an attractively designed book – far more appealing than most gardeners expect from a serious plant monograph even though the predominant colour of ivies is, well, green. All the species are described in detail, but not in torrents of baffling technical language; two hundred cultivars are illustrated and described, and the fat descriptive checklist covers all the other names that have ever been used, over two thousand of them.

One very useful feature of the book is its use of the Pierot system of classification. This was created by Suzanne Pierot, the first President of the American Ivy Society, in the 1970s and divides ivies into nine convenient groups based on easily-seen features of the foliage. Brits are largely unfamiliar with this approach so its use in this book should help it stick.

But what does the book have to say about those pros and cons?
Attractive foliage? Obviously.
Good for wildlife? Yes. “Ivy berries are eaten by at least 17 species of bird in Britain indicating the importance of this plant group for the support of vertebrate wildlife…. They have a high energy, though low protein, content and form a large part of the diet of several species at this time of year (winter).” “The autumn flowering of ivy provides nectar for a wide range of invertebrates at a lean time of year.” Not to mention ivy as a valuable nest site.
Cools buildings in summer, warms buildings in winter? Yes. “Measurements on ivy-covered stone walls across several historic sites in England… showed that an ivy covering resulted in cooler walls in summer and warmer walls in winter.” “Recent research on the climate of southeast UK… suggests that a 21-37% reduction in winter heating could be achieved.”

Invasive? Sometimes. While most ivies can develop vigorous growth in their native habitats, it is almost always H. hibernica that causes problems as a non-native plant. “All ivies need not be banned in climates where invasive ivies are a problem. There are enough dwarf, miniature and slow-growing cultivars of H. helix to provide a good range of safe and attractive plants for indoor and outdoor use.” In my Pennsylvania garden, as soon as an ivy shoot penetrates the deer fence the deer eat it.

Damages walls? Sometimes. “Any increase in relative humidity due to wall plant cover is offset by lack of rain reaching the building.” But: “ivy can root into weakened historic walls or buildings, and can lift blocks of stone off walls” and also damage walls built and pointed using soft mortar.

Harbours pests? Sometimes. Ivy is attacked by viburnum scale which also attacks Viburnum tinus. “In pots, by far the most serious pest of ivy is vine weevil” – which attacks a wider range of other plants. I’d be interested to know if outdoor ivy has a role as a reservoir of vine weevil infestation.

This is an impressive book by one of our most seasoned horticultural taxonomists and a relatively young recruit to the RHS botany team. The RHS has more in the series on the way, I look forward to the series building into an invaluable resource.

Hedera: The Complete Guide by Hugh McAllister and Rosalyn Marshall is published by the Royal Horticultural Society at £40.00/$53.45.

You can read more about ivies in gardens and in the wild in these Transatlantic Gardener posts.
Ivy is not always a menace
Ivy reveals how nature is nuanced
Ivy goes green

 The outstanding new perennial I grew this year was in the garden only by chance. Heliopsis ‘Burning Hearts’ was a trade from Ian Hodgson, Editor-at-Large for the UK weekly magazine Garden News, and it’s been exceptional. I passed him some new heucheras, he gave me the heliopsis.

This hardy bronze-leaved perennial is a form of the North American native H. helianthoides var. scabra which grows in much of the east and south of the USA as well as in Canada. A number of things impressed me about ‘Burning Hearts’.

I planted three young plants, raised from seed Ian had sown earlier in the spring, in mid May. The purple-bronze foliage was impressive straight away, the plants grew away well and in June they were in flower. They’re still flowering today at about 90cm/3ft, in spite of being partially shaded by the unexpected vigour of a new physocarpus (not to mention some rampageous climbing beans).

The bright, slightly golden yellow petals are rolled back gently from the dark eye, each one stained red-orange at the base, and are perfectly shown off by those dark leaves although the red centres fades as the individual flowers age. The plants have been dead-headed regularly and a long succession of stems have been cut for fiery bouquets. They’ve been amazingly productive.

Jelitto Perennial Seeds, who developed ‘Burning Hearts’, point out this is like a supercharged version of ‘Summer Nights’ with darker leaves and flowers in more dramatically contrasting colours. They say it’s been in the works in Germany since 2004 when, the catalogue from Jelitto reveals, “the idea for ‘Burning Hearts’ came in a dream”. Hmmm…

Gardeners in both Britain and North America can order seed of H. helianthoides var. scabra 'Burning Hearts' from Jelitto Perennial Seeds.

Back in March, I started to create a trial garden, a test garden if you like, in Northamptonshire. The idea was to grow new, recent and upcoming varieties so I can report on them from experience as well as grow cut flowers and vegetables. And that’s exactly what I’ve been doing.

During winter, my friend and helper (and artist) Carol Parfitt made a start by digging out bindweed and just about everything else that was growing in the plot leaving me a clear canvas. Then I made a series of rectangular raised beds using 15cm (6in) pressure treated boards, each bed is 1.2m (4ft) wide with 60cm (2ft) paths between.

The soil is good: old English cottage garden soil that has been improved with soot and compost for generations (not to mention, in earlier days) enrichment from pigs and chickens. Most of the new beds had soil improver added.

Things were a little late getting going, after all I was making beds long after planting and sowing time for many varieties. But as soon as each bed was ready, plants and seeds went in. Then I’d make the next bed, and more plants went in.

Weeding has been a big issue, the tiniest slivers of bindweed root will grow, after all, and moving soil around exposed the seeds of annual weeds which soon germinated. But regular weeding has kept them down and only what Brits call the Duke of Argyll’s Tea Plant (Lycium barbarum) has proved a lasting problem. More about that another time.

The trials of leucanthemums and cosmos and clematis and calendula have been fascinating. Leucanthemum ‘Real Glory’ (below) has been a real star. We’ve had more cucumbers and tomatoes and zucchini than we could cope with (though not enough lettuces). Cut flowers have filled our tables and windowsills and been given away and there’ve been successes and failures amongst the American varieties I’ve been growing in Britain for the first time.

Through the autumn I’ll be discussing some of the results of this year’s trials here and also on my Plant Talk blog for Mr Fothergill’s. Please check back and take a look.