Anna Pavord: Tall plants

Despite our columnist’s best attempts to rein in her most enthusiastic plants, some of them are determined to shoot for the stars

Monkshoods provide a variety of blues (Alamy)

Memo to self. Do not grow so many tall plants next year. Unfortunately, self has a way of disregarding memos if it happens to suit. But as I was dismantling the flower garden ready for winter, I was forced to confront the fact that an awful lot of it was propped up on canes eight or 10 feet long. It's not even a very big border, but the plants I like – angelica, fennel, ammi, the magnificent late-flowering Salvia dombeyi – all want to tickle the clouds. Even the excellent agastache 'Blackadder', newly introduced to the garden this year, has grown to over two metres.

Two metres? Nothing I'd ever read about it suggested that 'Blackadder', with its furry, fat spikes of purplish-blue flowers, would want to push on beyond four. But it's caught the tall bug. It's been flowering at crick-neck height with its neighbours, the fennels and spurges. I'm hoping after this teenage flexing of muscles, that it'll become less competitive and flower in the mid-storey, which is where I really want it.

In a general sense though, I've been impressed by 'Blackadder'. Though it got so tall, it hasn't needed staking and it flowered non-stop from July until the end of October. The flower spikes are like narrow bottle brushes, built up of tight whorls of small lippy flowers. Only a few in each whorl will be out at the same time, but because, overall, there are so many of them, it looks as though you have a fully-flowering spike. Insects of all kinds have loved them.

It's not a showy plant, but you can't have a border made up entirely of stars screaming "Look at me". You need a good-natured supporting cast, too. 'Blackadder' has flowers of an easy colour, easy in the sense that it will fit with yellow and orange as easily as pink or purple. And it flowers for a long time, which is a huge advantage. Stars usually blaze for a shorter period, so you depend on these supporting plants to stitch the border together between one major incident and the next.

The major incidents are easier to sort out. With us they are tulips, iris and lilies. But none of those have much besides their flowers to offer. So the border needs plenty of stuff with good foliage to fill it out and provide a backdrop for the stars. There are three families of plants I depend on more than any other to do this: spurges, thalictrums and monkshoods. Between them they cover pretty much the entire year, with the stars blazing away between them from March (species tulips) to late August (lilies). 'Blackadder' has now joined this useful gang of three.

Who knows why we are drawn to some plants more than others? To a certain extent, I can defend my choices. Spurges have excellent foliage and several of the ones I use in the flower garden (Euphorbia mellifera and Euphorbia characias) are evergreen. Thalictrums also have good leaves, finer, lighter, airier than those of the spurges, and often with a greyish, glaucous wash which is very useful alongside bright green, as in the beefy, strap leaves of agapanthus, for instance. It was one of the very slow lessons I learnt when I first started to garden. If, in putting plants together, you concentrate on leaves, thinking about contrasts of colour, texture and form, then the flowers will look after themselves.

I can't make a strong case for the foliage of monkshoods, but it is dark green > and glossy. The gloss is the most important factor. I grow them because I don't grow delphiniums (too much sweat), and between them, the flowers of the various monkshoods give you many of the wonderful blues that you get among the delphinium tribe. The spectrum runs from ghostly 'Stainless Steel' which has pale blue flowers flushed with grey, to 'Spark's Variety' which has the deepest coloured flowers of any monkshoods, a purplish navy-blue.

They flower for a long time because once the main spike at the top of the stem starts to go over, subsidiary spikes come into flower all the way down the stem. But there are three different things to juggle with in this family, not only colour, but height and flowering time, too. Somehow I've ended up with too many tall ones, such as 'Kelmscott', which grows to at least two metres. Many of the best ones, such as 'Arendsii', stick at around 1.2m and that's the one that is on my shopping list for next spring. There was a big space in the border with nothing in it but forget-me-not which I've now ruthlessly chucked. I'm looking forward to seeing 'Arendsii' with its mid-blue flowers filling the gap instead.

Most monkshoods perform from late summer on, but 'Stainless Steel' often starts in June. From then on, by choosing varieties carefully, you can have monkshoods performing right into November. Follow 'Stainless Steel' (June to July) with 'Spark's Variety' (July to September), 'Arendsii' (August to September), 'Kelmscott' (September to October' and 'River Nene' (September to November).

But it's interesting, too, thinking about the reasons you don't choose some plants as companions. There aren't any daylilies in our garden, for instance, though the fact that there are nearly two and a half thousand different kinds listed in The Plant Finder suggests they are generally very popular with gardeners. Why aren't they here? Well, for a start, I don't need any more strappy foliage. Many of the irises have it, as well as the crinums and the alliums. So do the agapanthus, and we have plenty of those.

Then there's a beefiness about the structure and texture of many daylilies which is unattractive. There are exceptions, such as the yellow Hemerocallis lilioasphodelus, but that is a light-limbed species that flowers as nature intended. Man-made varieties often seem lumpen in comparison. A psychiatrist, of course, could have a field day with one's prejudices. I grew up in Wales, where I always felt like a crane among linnets. Perhaps I choose tall plants for the flower garden because I feel more comfortable among things that are built on my sort of lines. But still, I think I'll print out that memo and pin it in the potting shed.

Weekend Work

WHAT TO DO

* The snowberry, 'Symphoricarpos albus', gets overgrown and overtwigged as it ages. Thin out some of the most densely twiggy stems, cutting them down at ground level.

* Continue to plant tulips. They are excellent in tubs and windowboxes, especially the shorter varieties and those with decoratively striped leaves, such as the Greigii and Kaufmanniana types. 'Daylight' is brilliant red with a yellow striped base and only 15cm high.

* Continue to plant hyacinths in bowls to flower in January and February. Leave dahlias and begonias in the ground as long as possible before lifting. The tubers do most of their growing in the short days of autumn. Lift them only when the foliage has been blackened by frost.

WHAT TO SEE

* In most areas of Britain, garden visiting comes to a halt when the leaves have fallen from the trees. Not in Cornwall, where the garden at Trevoole Farm, Trevoole, Praze-an-Beeble, Camborne TR14 0RN, is open every Thursday (10am-4pm) until 18 December, admission £3. The gardens surround an 18th-century farm with a fine yard of granite outbuildings. Call 01209 831243 or visit trevoolefarm.co.uk