Downfall of the Rambling Rector came to r

The first rule of pergolas is a stout structure. Then the clematis and climbing roses can be allowed to run riot, says Anna Pavord

Is it only us who have collapsing pergola problems? It is not a question you see raised very often in the gardening press. "Dear Ed: 'Rambling Rector' and 'Dorothy Perkins' collapsed in a heap on the ground. What can I do?"

Although it is disloyal to say so, I was not particularly surprised when the Mark I pergola blew over. My husband had made it from elm branches and the supports were not buried deep enough to give the structure any stability. Eddie, the do-it-all wizard of our area, was called in to start it all again with fat larch poles set in concrete foundations.

The foundations are still stout enough to support a house, but in a summer gale when the pergola was loaded with its top hamper of rose and clematis and vine, some of the poles snapped off at ground level, bringing the whole airy tunnel of green crashing to the ground. The wood had rotted through.

We are now on our third set of poles, pumped with enough preservative to keep a museum full of mummies on their feet. But, walking down the path yesterday evening, I felt oddly seasick. Two of the middle poles were conspicuously un-upright, leaning in neat parallels with their loads of 'Goldfinch' and 'Gloire de Dijon' roses, 'White Columbine' and Ascotiensis clematis. Another disaster looms.

It is no good dreaming of a pergola reconstituted Arts and Crafts style, with fine brick pillars and oak overthrows. If finances cannot run to a new wheelbarrow (ours is what a visitor politely referred to as "self- draining"), they certainly will not stretch to Lutyensesque creations of that kind.

I have consulted all the books to hand about garden design. There are helpful illustrations about crossed half-jointing, ogee curved-end detailing and the like, but a conspiracy of total silence on the business of rot at ground level, however deep the foundations. I think this means we have got to live with the problem and replace poles as they fall.

We have fitted splints to some uprights, by knocking in three angle-irons round the base to clasp the pole as if in a neck brace. This is a bodge- up, but when the tendrils of clematis start doing their stuff, you do not see the splints. When the poles do go, I find the easiest thing is to cut most of the growth of the climbers to the base, and start again.

With rambling roses such as 'Rambling Rector', which has relaxed clusters of tiny cream flowers, this is no bad thing. It rejuvenates the rose and means you can get growth to furnish the lower parts of the poles. The problem with roses on pergolas is that they do much of their flowering too high. Because it is such a business untying them all for pruning, you tend to be lazy about cutting out old wood and content yourself with tying in new. Then, gradually, you find less and less new wood springing from the base, where you want it.

Damage to the roots of existing plants seems inevitable if you are excavating foundations for a new post. They need to go 2ft down. If you dug that deep with a spade, you would indeed do a great deal of damage, but professionals use post borers, like giant corkscrews, which take out a long plug of earth not much thicker than the post itself. This generates much less mayhem in the root area and so far I have not found that any plants have suffered from the work going on around them.

Even plants that you are not supposed to cut down to the ground, such as Clematis macropetala, which I have growing through the rose 'Easlea's Golden Rambler' on the pergola, recover fast. They were on another pole that crashed rather messily into the raspberry patch. I saved one long growth of the rose and cut back the rest to the ground, but it has responded superbly, putting out five juicy new wands. The clematis has replaced itself even faster. I cut them both back in early spring.

I will not mind when Goldfinch's pole goes the way it obviously wants to go. This rose has been a grave disappointment. It scarcely ever flowers and it was a bad choice in the first place. It is more suitable for a pillar than a pergola, for it grows only 8ft tall. That is enough to cover the uprights, but it certainly does not give you anything spare which you can use to train along the top of a pergola. I chose it for its colour - pale cream - and for its thornless stems.

There is nothing more irritating than roses grabbing at your hair when you are trying to prune them, balanced on a wobbly stepladder. This part of the pergola is supposed to be purplish and creamish. So far, the best performer has been Solanum crispum 'Glasnevin', planted six years ago. Its purple potato flowers have already been out for six weeks and will continue in waves all summer.

It is important to seek out the cultivar 'Glasnevin' because it flowers much more freely and over a longer period than the species. It is also hardier. The solanum meets 'Easleas's Golden Rambler' over one of the cross pieces of the pergola and the two are flowering together now in a ludicrously abandoned way. This rose is one of my favourites. It is vigorous and the foliage is dark and glossy. The flowers are very full doubles, not golden at all but a pale, washed-out primrose. They smell swoony.

It is a Thirties rose described rather pathetically as "of unknown parentage" and, although on our pergola it grows in full sun, I have also seen it doing well in shade, even the uncompromising shade of a north wall. In spring, before it begins to flower, it is draped with the early flowering blue Clematis macropetala. Most of the climbers on the pergola have attendant clematis hanging on to them. The solanum has 'The President' as a companion, dark purple flowers with silver backs, not overpoweringly large.

In a narrow border under the pergola, I am trying to establish a ribbon of iris. As a gardening correspondent, I am always urging people to go with the flow of their gardens, not to struggle with plants that would be happier elsewhere. As a gardener, of course, I completely disregard my own advice and persevere with bearded iris, though they hate our clay.

In Cornwall this week at Penpol House, Hayle, I was stopped in my tracks by a band of bearded iris about 4ft wide fronting an old shrub border. What did he do to make them grow so well? I asked the owner, Major Ellis. "Oh, nothing much," he replied. "Just dig them up every three years."

I wish I had enough to dig. Only the most common deep purple kind (which happen to look well with the solanum) show any sign of increasing. There are eight spikes of flower this year. The posh ones such as 'Blue Rhythm', which has lemon-scented cornflower blue flowers, and 'Love Chant', which is white with a rich tangerine-coloured beard, hang on but do not increase.

In July I must steel myself to lift them all, dig in more grit, coarse sand and bonemeal and replant the trimmed rhizomes. They need to sit with their tops above the soil so that they can bake in the summer sun.

Penpol House, Penpol Avenue, Hayle, Cornwall is open 18 and 25 June, 2 July (2-6pm). Admission pounds 2. Also open by appointment on 01736 753146.