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A Northumberland Alpine Gardener's Diary

This entry: 22 September 2010 by John Richards

Northumberland Diary. Entry 160.

Potentilla fruticosa

The shrubby cinquefoil is a garden staple, which I suppose can be found in most collections. It is an excellent subject in many ways; easy on a wide variety of soils and sites; long lived, with a long flowering period each late summer; and only requiring a clip over once the flowering has finished. It lacks, perhaps, that extra 'something' that the plantsman looks for in the most desirable subjects, but in many ways it is hard to fault.

Botanically, Potentilla fruticosa is the most fascinating subject. Consider firstly its strange, fractured distribution. In the British Isles it is confined to the rocks beside the River Tees, the Wastwater Secrees in Lakeland, and the Burren, that limestone wilderness in western Ireland. It is scattered through the Pyrenees, but is absent from the Alps. It is found on the Baltic Islands Oland and Gotland, in the Urals, the Himalayas and western China through to Japan, and across arctic Canada and down the Rockies. Defintely, this is the relictic range of an ancient species, a forerunner of the rose family perhaps.

There are other oddities about this species. In some parts of its range, for instance Britain and Ireland, it is dioecious; different plants are either male or female. In other areas, such as the Pyrenees and all of America it is hermaphrodite. Remarkably, it is the dioecious races that are tetraploid or hexaploid, with four or six sets of chromosomes while the diploids are hermaphrodite; usually it is the other way round, not least because genetic gender control can be upset by polyploidy. Even more remarkably, the shrubby cinquefoil is one of very few living things in which the heterogametic gender (the one with the Y chromosome) is female, rather than male (dioecious strawberries, Fragaria, from South America are another; this genus is close to Potentilla).

Many, many years ago, in 1972, one of the first undergraduates I taught, Clare Kitchen (as she is now), undertook a student project on Potentilla fruticosa in upper Teesdale, and, later, studied the seed germination. We raised 84 plants to flowering (1974) and examined their gender, finding that there was a large and significant excess of females. Thirty-six years later we still grow these plants in our Botanic Garden; there have been many casualities and some (natural) replacements, and today there are about 66 plants Now males slightly outnumber females. Female longevity has been much poorer than that of males. As a Card-Carrying member of the Y chromosome club, I blame the latter! By the way,these days Clare is, with her husband Mark, Botanical County Recorder for Gloucestershire and among Britain's best known amateur Botanists.

Another striking feature of Potentilla fruticosa is its amazing variability which has been much used by plant breeders. Flowers can be white, lemon, yellow, gold, tangerine, pink or red. Plants can be prostrate or 1.5 m tall. Leaves can be green and hairless or white-lanate. Flowers can vary in diameter by a factor of at least three. And so on. Nearly all of these seem to grow relatively easily, but the high alpine dwarfs (sometimes called P. pumila) can be tricky. With a species of such a wide geographical range and ecological plasticity, such variability might not be considered surprising. However, I found that in one locality, the Zheduo Pass above Kanding in Sichuan it was possibly to find white, lemon or gold flowers, white or green foliage, and prostrate to erect plants, all within a kilometre or two. Despite many efforts to subdivide this species into different taxa, it is clearly just one very variable entity. Here is a lovely golden prostrate plant from the Zheduo.

We grow a number of distinct varieties here. Firstly, here are P.f. 'Elizabeth' (formerly known by the invalid name arbuscula' ) which we found in our last garden when we moved there in 1976, and P.f. 'Goldfinger, a modern variety which we bought as recently as 2002.

Next 'Tangerine', grown from cuttings taken from my mother's plant in Reading, and 'Red Ace', propagated from Alan Furness' plant.

Finally the white 'Manchu' (once separated as the species P. mandschurica) and 'Princess'. I think I am right in saying that the pink Princess was the first pink 'break' in the group. Many more pink varieties are available today.

Autumn clematis

Another genus which is providing colour at the moment is Clematis. Some of these are genuinely late-flowering, such as C. orientalis and C. viticella 'Etoile Violette' (scrambling through Salix lanata).

Autumn clematis

Clematis 'Jackmanii' and C. 'Hendryetta' have been on the go for a couple of months

In contrast, 'Nelly Moser' should have flowered in the spring, but it was cut to the ground as part of hedge reparations, and is only now starting to produce a few late flowers on regrowth.

Bits and pieces

As usual, after the August gap, September is proving a good deal more interesting. We struggle with most hydrangeas here (H. paniculata is a notable exception) and the fascinating H. quercifolia has had a very varied history. In fact, after the last hard winter it looked dead. Far from it. It has rebounded with surprising vigour and is flowering relatively freely, which is almost unprecedented  in this garden.

Bits and pieces

Another plant I have featured before which helps to make September worthwhile and surpasses itself here is Kirengeshoma palmata. I have long accepted this as a member of the saxifrage family, but see now that it is placed like the last subject in the Hydrangeaceae. Unlike most in this family, it is a herbaceous perennial which thrives in our shelter and woodsy soils. Peter Bland (see below) says that the flowers of his plants rarely open. As you see, they do here, I suspect merely because I have come across a better form.

Proceeding to Sheila's border, a planned association of two coincident late-bloomers is taking the eye. I am afraid I have no idea what the aster is. The yellow daisy is of course the yellow form of Anthemis tinctoria.

Nearly all primulas flower in the first six months of the year (which are therefore vastly preferable!!). Only a small handful flower late in the year by choice, and of these by far the best known is P. capitata, particularly in the subspecies sphaerocephala. As is well known, this is a short-lived plant, even a biennial, but it is scarcely credible that this group was sown in January and germinated in April! Truly, the growth of many primula seedlings this summer has been phenonemal!

As I mentioned last week, when I wrote I was about to visit another Group as a speaker, and so it was that I was in Lancaster on Thursday, seeing many old friends. I spent the night with Peter and Beryl Bland, good friends who also have what is in my view a garden which is very high on a very short short-list of the best alpine gardens in Britain. As is well-known, Beryl holds the National Collection of silver saxifrages and has won awards for the standard of her collection. It is indeed exactly what a National Collection should be. Comprehensive, very expert, beautifully curated, data-based, labelled and organised, and, importantly, concerning plants which propagate well vegetatively, do not catch nasty diseases from one another, and are long-lived (and compact!). Here is just a small part of the collection.

I said they do not catch diseases, but the collection is not without its pests, for rabbits love to burrow in the soft sand plunge! Hence all plants are covered with black netting. As you see most plants are grown in pots. However, many are also planted out in immaculate raised beds planted amongst limestone and tufa, where they look wonderful.

Peter is perhaps best known for his very extensive collection of rare species rhododendrons, and unique hybrids which he has raised himself. However the Blands also have a series of beautifully designed rock gardens, of which this is but one example..

Peter runs no less than three alpine houses full of rare and difficult plants. He rarely exhibits these at Shows, which is a shame in some ways, but good news for the rest of us! Here is just one example; one of the best Androsace delavayi I have seen for some time.

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