My sister has become a great gardener – and I have never felt so betrayed

I left a houseplant outside, not because I didn’t know it was a houseplant – I had been told: “This will look nice in your kitchen” – but because I assumed plants were like rabbits: whether you called them indoor or outdoor, they always prefer to be in the garden. It sickened over time without my noticing, to the point where I had to send a picture of it to my sister. She said: “Yes, this is a houseplant, which you are killing,” then sent me an instructional video about how to rescue it.

As I was watching it, I couldn’t help noticing the timbre of her voice – Prue Leith levels of certainty and expertise with a Gregg Wallace can-do attitude – and the jungle of succulents on her table; tiny, creepy verdure bursting out of terraria – with the garden vying for attention through the window, full of … well, full of damn plants.

When did that happen? When did she become someone with the patience for gardening? It’s not as if I never go to her house – I was there a week ago. I just didn’t register that the junk on her surfaces wasn’t junk any more – it was alive. It was like discovering she could speak German. I felt simultaneously impressed and betrayed.

I thought we had figured out what kind of family we were years ago: sowers of chaos; bringers of entropy; people who are afraid of slugs. “Don’t you remember when she came over to plant the red hot pokers?” Mr Z asked. “It was only a month ago.” No, I don’t think I even knew she was doing that. I thought she was just getting some fresh air.

In the time between me receiving the houseplant and spurring its demise, the person that it originally belonged to also died and it became a matter of primary importance that it be saved. My treacherous, green-fingered sister sent me another video, then some suggestions on compost. The plant started to look less forlorn. It wants to live, I realised. How obscurely satisfying. But no way, gardening world: you don’t turn me that easily.

• Zoe Williams is a Guardian columnist