Four winters of windowsill herbs, and what finally worked
Over four winters I have killed enough basil to fill a compost bin, and I would like to write down what I learned before I forget it and buy another doomed pot in March.
The setup, so you can judge how much of this applies to you: a second-floor flat, one kitchen window facing north-northeast, a sill about eleven centimetres deep. From May to August that window gets perhaps three hours of thin direct sun. From November to February it gets none at all — only the flat grey light that makes everything on the counter look like a photograph of itself. By any sensible standard this is a bad place to grow herbs. I have grown herbs there anyway: badly for a long time, and now tolerably.
The mistake I kept making
For three years I treated supermarket herb pots as plants. They are not plants. A supermarket pot of basil is twenty or thirty seedlings sown at once into a plug of peat the size of a shot glass, forced under lights, and sold to be eaten within about nine days. Everything about it — the density, the soft growth, the permanently wet compost — is optimised for looking lush on a shelf on Thursday.
It isn't a plant, it's a bouquet. You wouldn't be upset that cut flowers died.
— a friend who spent a decade at a garden centre
Once I stopped taking that personally, things improved. I still buy those pots, but I buy them knowing what they are. Half gets eaten the same evening. The rest I tip out, ease apart into three or four clumps with some root on each, and pot on into ordinary compost. Perhaps one clump in three survives the move. That is an enormous improvement on none in one.
What actually changed things
Four things, roughly in the order of how much difference they made.
Fewer plants, bigger pots. I run five pots now instead of eleven. A 15 cm pot holds enough compost to survive a forgotten weekend; a 9 cm pot goes to dust in one warm afternoon and takes the roots with it. Small pots are a false economy in every direction except shelf space.
Terracotta, and accepting that it dries out. Plastic holds water so evenly that I could never tell by looking whether a plant wanted anything. Unglazed terracotta goes dark when it is wet and pale when it is dry, which turns watering from a guess into a glance. It does mean watering more often. I consider that a fair trade for never again drowning a rosemary.
Moving everything off the radiator shelf. This one still embarrasses me. For two winters the pots sat on a shelf directly above a radiator, because that was the warm bright corner and I assumed warm was good. It is not. The rising dry air pulled water out of the leaves faster than roots sitting in cold compost could replace it, so the plants browned from the tips inward while the compost stayed damp. I read that as thirst and watered more, which rotted them. Moving the pots sixty centimetres sideways solved a problem I had been misdiagnosing for a year and a half.
One cheap clip-on lamp, used honestly. I resisted this for a long time because it felt like cheating, which is a strange thing to feel about a plant. Fifteen watts on a timer, twenty centimetres above the leaves, twelve hours a day from November to February. It is not a grow room. It is the difference between basil that sulks and basil that grows slowly.
I kept a note on the fridge door for one winter, mostly so I would stop lying to myself about how often I watered. Transcribed as written:
Nov 3 repotted 2x thyme, 1x parsley — 15cm terracotta Nov 9 lamp on timer, 07:00–19:00 Nov 17 parsley yellow at the base. too wet. skipped a week. Nov 24 thyme fine. mint growing like it is being paid to. Dec 6 basil from Tues shop: split to 4 clumps, 2 alive Dec 21 away 5 days, nobody watered. all alive on return. Jan 12 first proper cut of thyme since October Feb 2 parsley bolting already. pull it in March.
A short and unfair ranking
- Chives. Effectively impossible to kill, first thing up every year, and they do not mind being cut to the ground. Start here.
- Mint. Also impossible to kill, but keep it in its own pot or it will quietly annex the others.
- Thyme. Slow, undramatic, still alive after four years. The best return per unit of attention by a wide margin.
- Parsley. Good for one winter, then it flowers and gives up. Treat it as an annual and stop grieving.
- Basil. Wants heat and light I cannot give it. I grow it anyway, badly, every summer, on purpose.
Two habits I have dropped entirely. Misting the leaves, which does nothing measurable for humidity and quite a lot for fungus. And feeding in winter — a plant growing at a tenth of its summer speed has no use for fertiliser, and the salts simply accumulate until the leaf tips burn. I picked up both of those from articles like this one, which is worth bearing in mind while reading articles like this one.
None of this is optimisation. Five pots on a north window will never pay for themselves, and the light will never be good. But in the second week of February, when it is dark by four and everything outside is the colour of wet cardboard, there is a shelf in my kitchen with something green on it that I did not buy that day. That has turned out to be worth considerably more than the herbs.