Sales of the feathery plant have plummeted – are innocent gardeners getting wise to its hidden meaning?

Name: Pampas grass.

Also known as: Cortaderia selloana.

Appearance: Big tufts of tough green grass with white feathery flowers protruding on huge stalks.

Location: The grasslands of southern South America, and suburban gardens all over the world.

Yes, I think I’ve seen it. Massive stuff. That’s right. It can grow up to three metres tall. It’s a good way to add some excitement to your front garden.

Why are you winking at me? There’s no need to be coy.

I’m not being coy. You’re being weird. We were having a nice chat about pampas grass and now your hand is on my leg. Is it? Goodness, I didn’t realise. But surely you know that besides being a groovy plant, Cortaderia selloana is also a secret symbol indicating that the people who planted it enjoy “the lifestyle”?

What, gardening? No. Swinging.

You mean on a swing? Oh, for heaven’s sake. I mean married couples swapping sexual partners.

What? So if I see some pampas grass I just go and ring the bell and whoever is inside will have sex with me? Not quite. You have to bring a partner to swap, and they might be busy when you ring, but in principle, if you get a dinner invitation, they’re up for it. Allegedly.

Crikey. There must be a lot sexual-partner-swappers out there. Yes, or there were. Sales of pampas grass have plummeted in recent years. The Telegraph spoke to a few garden centres, and they seem to be selling about half what they did five years ago.

Have people lost interest in adultery? Unlikely. It might just be that pampas grass has gone out of fashion. The leaves are quite sharp and nasty, and it can become invasive. Innocent gardeners may also have got wise to its hidden meaning. Mariella Frostrup planted some six years ago, leading to unexpected inquiries from neighbours.

A likely story. Still, at least in a few more years we’ll know for sure that the only people left with pampas grass are hardcore swingers. I guess we will.

Are you going to take my hand off my leg now? You seem tense.

Do say: “I blame decking and the eco trend.”

Don’t say: “I blame Tinder.”