The oldest jar at eighteen months: what a sealed system looks like now
The two-litre sweet jar was sealed on the 22nd of March last year and has been opened exactly once, for about ten minutes in July 2025, to pull out a leaf of the fern that had pressed itself flat against the glass and started to go translucent. Otherwise it has been left alone on the north shelf, about 60 centimetres from the window, at room temperatures that range from 17 degrees in January to 26 in a hot week in August.
The daily cycle is now very regular. By about nine in the morning the glass is clear. Through the day, as the room warms, condensation climbs the inside from the substrate upwards, so that by late afternoon the top two thirds are fogged and small drops run down the shaded side. Overnight it clears again from the top. If I wake and the glass is fogged at dawn, it means the night was warm and I open a window in the room rather than the jar.
The planting has sorted itself out without me. A small fern that went in as three fronds the size of my thumb now fills roughly half the volume and has sent fronds up to the lid, where they bend over and keep growing sideways. The cushion moss on the mound beneath it is dense and bright except for one corner furthest from the window, which has browned over the summer and is being colonised by a thinner, creeping moss that arrived on its own, probably as spores on the bark. The sheet moss on the slope is unchanged, which is to say still alive and still slightly dull.
Two things I did not expect. The inside of the glass below the soil line has developed a thin green film of algae that I can only see with a torch, and that I have decided to leave alone. And the water level, judged by the dampness of the substrate against the glass, has not visibly changed in eighteen months. I added 40 millilitres of rainwater at sealing and nothing since. Whatever is happening in there is balanced, or at least balanced enough, and I am inclined to keep my hands out of it.