Ivy reveals how nature is nuanced

Ivy growing on a stone wall. Image © (all rights reserved)In North America, in spite of uncertainty about exactly which species is involved, ivy is widely condemned as an invasive plant that smothers natural vegetation. And it’s true, whether it’s Hedera helix or H. hibernica that’s causing the problem, ivy can be a menace in some areas although in much of the country it doesn’t grow at all and in other areas it remains well behaved.

But seeing this ivy on the wall of an English stone cottage (left, click to enlarge) reminded me that ivy can cause other problems even in Britain where it’s a valuable native plant popular with insects and birds and a widely popular ornamental climber for walls.

It has clearly once covered this limestone wall but has been cut off at the root and most of the growth removed. But it’s still growing, rooting into the mortar and renewing its hold. Looks like a job for Round Up, now, because the mortar traditionally used between the stones is relatively soft; when it’s pulled off, the mortar tends to come away too. Click he picture to enlarge it and you can see.

On modern walls built of hard bricks and hard mortar, a completely opposite problem can arise. In the picture below (click to enlarge), the bricks and mortar are so hard that the short aerial roots with which ivy stems grip their support have failed to take hold well. The weight of a rainstorm has pulled the ivy right off the wall.

These situations serve to remind us, on both sides of the Atlantic, that enthusiasm for a plant, and condemnation of it, are not simple black-and-white issues. Nature is nuanced, rarely is a simplistic view justified.
Ivy falling off a brick wall. Image © (all rights reserved)

My Sweet Pea Book has a new rival

RHS Sweet Pea Trial 2011. Image ©
It's odd, reviewing a book that's in direct competition with one of my own. For my Sweet Pea Book now has a rival in Sweet Peas: An Essential Guide by Roger Parsons (Crowood Press).

Fortunately, Roger's book takes a slightly different tack from mine with more emphasis on growing for showing and on the Spencer types which dominate the showbench. and with less focus on old fashioned heirloom sweet peas and growing sweet peas as garden flowers. It seemed to me that with the British National Sweet Pea Society and its publications so focused on exhibitors, what was needed was a book that would appeal more to non-specialists.

So many gardeners love sweet peas, and have no intention of doing anything but growing them in the garden and cutting a few for the house, that I thought that in my book exhibiting could take a back seat - though the basics are covered. Roger's account of what is perfect in the shape of a flower, quoting the precise angle between the wings that is acceptable, is fascinating for the truly devoted but a step too far for most non-exhibitors.

My book describes a large number of different varieties of all kinds – I sat on a stool in front of them to write most of the descriptions and they're presented in an A-Z format. Roger groups his by the color classification of the National Sweet Pea Society but although he grows far far more than I ever have or will, he describes few in detail. Grouping them by color is a good idea - when my book is revised I'll be including recommendations of the top garden varieties in each color group.

But, you know, let's not do any more his-and-mine stuff. Who cares?! The books are aimed at different types of sweet pea enthusiasts – and the real fanatics will quite rightly buy both. Although I must mention the photography. The The Sweet Pea Book features some gorgeous studio photography by the award-winning photographer judywhite showing a huge range of different varieties and so helping gardeners choose exactly the colors they want.

To be honest, I'd say if your main aim is competitive exhibiting then buy Roger's book. If not, then buy mine. Better still buy both.

At the moment it's easier to get my book in North America and Roger's in Britain although both are available on both continents. Here are buttons to buy books, on both sides of the Atlantic. And don't forget you can find out more about The Sweet Pea Book at its very own website. Find out more about Roger Parsons at his website.



Valuable climbing dicentra relative

About ten days ago, here on the Transatlantic Gardener, I was talking about Dicentra spectabilis (as was). Then, after I’d posted that piece, I suddenly remembered one of its wonderful relations, a biennial American native climber called Adlumia fungosa, also known as the Allegheny Vine.

I grew this years ago in one of my earlier British gardens, in my picture (above, click to enlarge) it’s scrambling over an especially good form of Euphorbia characias called ‘Blue Hills’, raised by the great British plant breeder Eric Smith. The euphorbia is noted for its very long, very blue leaves.

The adlumia makes an overwintering rosette of very attractive, lacily divided foliage and then long, long, rather succulent shoots develop carrying strings of flowers in a slightly impure pinkish purple. It clings in the same way as clematis, by curling its leaf stalks round its support.

I was always impressed by the fact that it was shedding its tiny, shiny black seeds towards the base of the stems while there were buds still waiting to open towards the tips. It’s a really valuable climber to grow through shrubs in a sunny place.

It turns out that Adlumia fungosa is native here in Pennsylvania, though not in our county, but it looks like popular deer food to me so it’s surely on the decline. I’ve not seen it in the surrounding counties where it’s said to grow.

Looking it up in the book I mentioned in my last post, Bleeding Hearts, Corydalis, and Their Relatives by Mark Tebbitt, Magnus Lidén, and Henrik Zetterland (Timber Press), I’m reminded that it has an uncommon white-flowered form. I notice that Summerhill Seeds in the USA have a pale pink form, which looks very pretty. And seed of the normal form is available for shipping all over the world from Britain's Chiltern Seeds – which is where I got it many years ago.

But can anyone tell me where I can get seed, or plants, of the white-flowered form?

Best climbers for wet soil?

Lonicera,honeysuckle,Graham Thomas,wet soil,climber. Image © (all rights reserved) I’ve been looking into climbers for wet soil today, for something I’m working on, and the fact is there don’t seem to be very many.

The first one that came to mind was Smilax, because we have a great tangle of a one growing in a boggy portion of our woods here in Pennsylvania. But - how can we say this politely - it’s not very colorful. And its spines are vicious.

Over in England I’ve seen honeysuckle, Lonicera periclymenum, with its roots in ditches as it climbs trees on the bank so that looks promising and there’s now quite a range of varieties, including the prolific yellow-flowered ‘Graham Thomas’ (click to enlarge).

Virginia creeper, Parthenocissus quinquefolia, is often recommended as well as climbing hydrangea, H. anomala subsp. petiolaris. I’ve also come across the suggestion that climbing, or more particularly, rambling roses are good in wet soil.

It seems to be mainly the really vigorous roses – ‘Kiftsgate, ‘Bobbie James’, R. banksiae – that are suggested. I know a lot of roses like heavy soil but that’s not quite the same as wet soil. Any thoughts?

Akebia, Campsis, ivy, jasmine, Vitis palmata (which I’ve never even heard of) are also recommended in various sources.

To help, I’ve just ordered a book called Managing the Wet Garden by my old boss John Simmons, Curator at Kew years ago. It’s based on his experiences in his soggy English retirement in garden in Norfolk (Was he mad? Well, at least he got a book out of it!) . He knows his plants and has a good eye – so I’m sure it will be useful.

In the meantime - while I’m off out to ID the Smilax in the woods a little more precisely - any more ideas for climbers for wet soil?

UPDATE: Turns out it's the common (aka roundleaf) greenbrier, Smilax rotundifolia. Quite an attractive foliage plant but, this year at least, no flowers and no fruits - not that either are especially exciting...

Parthenocissus ‘Fenway Park’ – the original plant

Parthenocissus tricuspidata ‘Fenway Park’,Boston Ivy,Red Sox,Rare Find Nursery, Image: ©Peter del Tredici. A couple of weeks ago I was telling you about ‘Fenway Park’, the lovely yellow leaved form of the Boston Ivy, Parthenocissus tricuspidata, and how it was found as a sport on a plant growing on a building near the Fenway Park stadium in Boston.

Well, regular Transatlantic Plantsman follower Ron Rabideau of Rare Find Nursery in Jackson, NJ has done us all a great favor by sending me a picture of the original plant, as first discovered on that old apartment block near the stadium. And here it is.

The picture was taken by Peter del Tredici, who first spotted the plant on the way to the ball game and made sure it was propagated. Unfortunately the plant is now gone.

Isn’t it great to see a fine new variety at the moment of discovery? Thank you Peter and thank you Rob (and Anne at Rare Find for telling me the picture even existed).

And you can check out the original post about Parthenocissus tricuspidata ‘Fenway Park’ here. In that post I mentioned Plant Delights nursery as a source - they’re now sold out.

But Parthenocissus tricuspidata ‘Fenway Park’ is available by mail order from Rare Find Nursery.

A colourful climber gets its name…

ParthenocissusFenwayPark14978 Plants are discovered, and come by their names, in some intriguing ways…

One day in 1988 Peter Del Tredici of the Arnold Arboretum in Boston Massachusetts was walking to a sports game. He was on his way to Fenway Park to watch the Boston Red Sox (For Brits: They’re a big baseball team. Baseball? You know about baseball? OK.).

The dramatic self-clinging climber Parthenocissus tricuspidata grows on so many buildings in Boston that it’s long been known as Boston Ivy. As he walked to the stadium he noticed that there was a yellow-leaved shoot on a plant climbing up an apartment building. He begged some material to propagate and so when the plant was introduced it was called Parthenocissus tricuspidata ‘Fenway Park’.

It’s an impressive plant. The leaves open bright yellow and in a sunny situation they retain their color. In shade, the leaves tend become a limey green color. In the autumn the leaves develop fiery red, orange and yellow tones.

It just takes a moment and a good eye to spot a great new plant - and to give it an appropriate name. Now if only we had a picture of the yellow shoot on the plant on the building...

Parthenocissus tricuspidata ‘Fenway Park’ is available from Plant Delights Nursery (though their story is slightly different.) In Britain it’s also available from these RHS Plant Finder nurseries.

Surprising bicolored vine

As the fall color fades, with only the Japanese maples that featured in the snow still at their peak, a twining vine galloping up a birch tree caught my attention.

Celastrus scandens with bicolored fall foliage. Image:© With the birch leaves long gone, its fresh green foliage amongst the bare twigs caught my eye but now, as its foliage is starting to turn, it’s even more striking. Having been evenly green all season, many (but not quite all) of the leaves are green on one side and yellow on the other. Sharply divided by the midrib of the leaf, the two colours show up brightly side by side.

I didn’t notice any flowers or fruits on this vine earlier in the season - in fact I didn’t really pay it much attention at all until now – but I wonder if it’s the American bittersweet, Celastrus scandens. This is a vine that grows in this area – although at a slightly lower altitude so its leaves have dropped - and a bird could easily have dropped a seed.

I’ll be keeping a closer watch on it next season.

Good and bad pruning

Trachelospermum jasminoides, star jasmine The superbly scented Trachelospermum jasminoides is sometimes known in the USA as Star Jasmine or, because it's widely planted in the South, Confederate Jasmine. It's also known as Traders Compass - oddly, since iot has five petals. Anyway... A few years ago this was a vine you rarely saw in Britain, and when you did it was usually planted on a south facing wall where it benefited from the choice position or grown in a conservatory.

But with the increase in patio gardening providing more situations which are warm and sheltered, and with the climate changing, it seems to be turning up all over the place. But this self-clinging evergreen vine needs the right pruning to ensure it doesn’t get out of hand, yet flowers prolifically.

Just opposite my daughter’s house in a south London suburb, is a lovely specimen. It’s trained on a pillar at the front gate and so that everyone who walks down the street or calls at the house can appreciate the colour and the fragrance. So they must be pruning it right.

Actually, I saw the owner pruning it once. It was a couple of years ago, in spring, and they were simply going over it briskly with the hedging shears. In much warmer climates, like Florida where it’s even used as ground cover, it’s pruned after flowering in May or June.

Lavender hedge - never pruned As it happens, a couple of houses along the street is an example of really bad pruning – or rather the bad result of a complete lack of pruning. This lavender hasn’t been pruned for years so it looks terrible. And now it’s too late. The thing is: lavender usually refuses to grow if you get out the saw or the long-handled pruners and cut into old thick wood. Do that with this hedge and it will probably die.

Better to tear it all out, improve the soil and put in some new plants – which should be pruned after every flush of flowers, snipping back to just above the old wood.

Ivy is not always a menace

News arrives of an American insurance company getting their knickers in a twist (as we say in England) about ivy growing up the walls of a brick-built house. The broker passes on the message from the insurance company: “If you can't take the ivy down they may chose to not renew your policy.”

So – are they mad, or are they wise and prudent?

In its native habitat ivy, Hedera helix, clings to tree trunks using aerial roots which are produced from stems as they come into contact with almost anything: bark, bricks, glass even. The function of these very short roots is mainly support, although they do absorb some moisture too.

Ivyonhouse On a relatively new brick-built house, the bricks and mortar are so hard that the ivy roots cling without causing any problems. In fact the presence of ivy can be advantageous: it provides extra winter insulation, it certainly sheds water from the wall and keeps it dry. It also provides a valuable nesting and roosting site for songbirds and food for butterflies and birds. And I’ve seen ivy that covered a relatively modern brick wall from top to bottom fall off completely without revealing any damage at all. In that case it couldn’t grip sufficiently well to support itself.

On older houses - and in Britain that usually means houses built before about the 1930s - any problem usually arises because the mortar used between the bricks is softer and as those aerial roots grip then fragments are loosened. You can see from these pictures of ivy growing on a brick house built in the 1800s how it can get out of hand. But here the value of the ivy in keeping the wall dry is also important. More of a problem is the ivy getting under and loosening the roof slates – but with relatively few American houses built of brick or roofed in slate this is less of an issue in the US. Yet in the US ivy is regarded as more of a villain than it is in Britain.

A huge range of problems is attributed to it from the quite reasonable fear of damage to certain types of building to harboring both rats and bacterial leaf scorch (a significant disease of trees). What was interesting is in that in a recent exchange the prevailing opinion was “every little bit of damage we can do to ivy's reputation is a good thing” and “I have to give (the insurance company) kudos for showing leadership in this area”.

No one asked: is the insurance company’s attitude reasonable? And then you see comments like “English ivy is a menace everywhere” - when in almost twenty states it doesn’t grow at all and is only cited as noxious in two – and “ivy strangles native trees” when it doesn’t strangle trees at all, is most vigorous in trees whose canopy is already thinned by disease or other causes and whatever it does is not restricted to natives.

HederaRippleJytte600 Now don’t get me wrong: I’m not saying that English ivy is a saintly plant with no faults. It is indeed a menace in some areas, and the insurance company, in this particular case, may be taking a prudent approach. But in other areas it’s a valuable ornamental climber, an attractive ground cover, useful in hanging baskets in areas not cold enough to kill it and a pretty and tolerant house plant.

But it’s not invasive in states where it doesn’t grow. And is ivy’s value as shelter and food for wildlife, which is much appreciated in its native Britain, utterly redundant elsewhere?

Can we please have less hysteria and panic and more reality and reason?

New RHS clematis bulletin

ClematisBulletin500 The 21st – yes, the twenty first – Trials Bulletin from the Royal Horticultural Society has recently been published – and it focuses on Clematis alpina and C. macropetala.

Following a trial at the RHS garden which began in 1997, the RHS has published a bulletin which helps us in a number of ways. For a start, it makes clear the distinction between C. alpina and C. macropetala, with some very clear pictures. There are descriptions and pictures of the sixteen plants which were awarded the Award of Garden Merit following the trial. It also provides a selection guide, going through the plants, from white to pink to blue, specifying their features and flowering season. There are also some confusions over the names which are resolved.

This is a most valuable report, and you can download it free of charge here. And I should mention that because of the certainty of the naming, the descriptions and the excellent photography this bulletin is of value far beyond Britain where it was produced.

For information on the twenty other bulletins produced by the RHS following trials click here.