Victoria Summerley: A moment of unholy glee amid the gloxinias

The annual Open Garden day approaches in the Summerley household. During the next couple of weeks, grass will be mown, weeds will be annihilated, flowers will be inspected for less-than-perfect petals. Cakes will be baked. And teeth will be gritted.

The aim of opening for the National Gardens Scheme – which merits an entry in their iconic Yellow Book – is to raise money for charity, particularly those specialising in cancer support and palliative care such as Macmillan and Marie Curie. Indeed, the NGS is Macmillan's biggest single donor. But one could be forgiven for the suspicion that the idea is really to give other gardeners the chance to use your plot as a yardstick by which to measure their own horticultural efforts.

The Independent's gardening writer, Anna Pavord, warned me about this before I opened for the first time. "They'll want to talk about their gardens more than they want to hear about yours," she said, sagely. This is my fourth year in the Yellow Book and I can vouch for the truth of this. I'm now used to the people who tell me their cannas are much bigger than mine, or that a friend's agapanthus are so abundant as to be a positive nuisance (unlike mine, which have produced two spindly flowerheads), or that a sister-in-law's garden is a sea of fragrant lilies (while mine have been nibbled to death by lily beetles).

It's funny the way gardeners seem incapable of resisting a bit of oneupmanship. The same people would not dream of coming into my living room and saying: "Goodness, my sofa is much bigger than yours" or "Your coffee table is looking a bit leggy, isn't it?" They wouldn't say: "My daughter's hair is a much more attractive colour than your daughter's," or "My son is much more good-looking than yours." No one has ever yet criticised or made odious comparisons with the home-made cake we serve. They'd think it was terribly bad manners. Yet in the garden, such observations are considered polite conversation.

I don't get at all offended because I'm exactly the same when I go garden visiting. I take enormous, secret pleasure in spotting some choice specimen that is half the size of the one in my garden. I feel sorry for (but a bit smug about) people who have box blight, because so far (touch boxwood) mine has escaped. It's traditional to trim box hedging or topiary around Derby Day, ie at the beginning of June, but I like the young green growth so I don't trim mine until the middle of August when, coincidentally, the conditions are likely to be less favourable for blight.

On a visit to Pashley Manor in East Sussex a couple of years ago, I was so delighted to see bindweed in the kitchen garden that I took a photograph of it as a permanent reminder of an ecstatic moment of schadenfreude.

I think this is the key to the whole comparison game. Gardening is such a precarious affair that those of us foolhardy enough to get involved in it will snatch greedily at anything that might provide a meagre seed of comfort.

I know very few gardeners who did not lose plants in the last long, horrendous winter. Then, as soon as we found the nerve (not to mention the money) to re-stock, those of us in the south-east had weeks of drought. Not exactly ideal circumstances in which to cosset newly planted specimens. If it's any consolation, while I might not have box blight, my box has become very stressed in the dry conditions and I am having to fuss over it with a hose in one hand and seaweed fertiliser in the other.

Meanwhile, there are all the other things with which gardeners contend: aphids, blossom end rot, canna virus, deer, earwigs, ground elder, honey fungus, Japanese knotweed, mildew, phyophthora; rosemary beetle, slugs and snails, squirrels, tomato blight, vine weevil, verticillium wilt. And as if that wasn't enough, it seems that almost every day there is news of some hitherto unknown disease or pest that threatens to wipe out swathes of Britain's gardens.

So we deserve our moments of triumph whenever and wherever we can find them. If you want to come and have such a moment in my garden at the end of the month, please feel free. Just don't criticise my children, or the cake.

Size matters

The Royal Horticultural Society is in full summer holiday swing at the moment, with activities for families at all its gardens. It's not always a happy mix – there is the occasional harrumph as a serious plantaholic in search of the rose garden meets a pack of ankle-biters in search of an ice cream.

In general, however, I'm in favour of children being introduced to gardens as young as possible. I like to think that when they grow up, they'll catch the scent of lavender, roses and mown grass and without quite knowing why, it will make them feel happy and want to grow some themselves.

One item designed with children in mind is a page on the RHS website called the Mostest Plants ( www.rhs.org.uk/Children/For-kids/Mostest-plants). It's a list of record-breakers, such as the stinkiest plant (titan arum) and the tallest tree (coast redwood).

I could imagine children being fascinated by these facts but what came as more of a surprise was the reaction of adults. My colleagues, more used to discussing the fortunes of Liverpool FC or the latest Test score, were intrigued to discover that the oldest living tree was 4,767 years old. (It's a bristlecone pine in California.)

One workmate mentioned the biggest fungus, a honey fungus measuring 3.5 miles in diameter. It's in Oregon, thank goodness. Another remembered reading about quaking aspens, which form large stands of what look like trees but are actually stems of the same plant connected by a single root system. The largest one, in Utah, covers 106 acres.

The speediest seeder was not nearly as exotic. One of these plants can produce 1,000 seeds, which can get through their whole life cycle in five or six weeks. It's found in the UK and it is the common or – if you're unlucky – garden groundsel.

Victoria Summerley's garden at 28 Multon Road, SW18 3LH is open for the National Gardens Scheme on Sunday 29 August from 2-6pm, admission £2.50 (children free – and very welcome). To read more about the garden go to www.victoriasbackyard.co.uk