GrowDAY 038

Chapter 01 · 3 min read

Why let the weather decide?

A garden nobody controls: one real day of Heilbronn weather, one choice, one commit – forever.

Most generative art is generated by someone: a seed you pick, a parameter you tune, a button you press. Grow has a gardener, but the most important force in it is not under anyone's control. It is the weather in Heilbronn – the real one, measured, one day at a time.

One day of sky, one choice, one commit

The garden lives in a public GitHub repository. Its whole state is one file, world/world.json. Every morning at 08:53 a Claude routine asks Open-Meteo what the weather was like yesterday at 49.14° N, 9.21° E. That day is reduced to one of six conditions, and the condition acts on the garden first:

  • Rain grows. Every plant in its growing season grows one stage – two after a downpour – and the stream rises.
  • Sun ripens. Blossoms open, apples ripen, the stream sinks and the sand banks grow.
  • Frost stops. Nothing grows, the stream freezes, the sunflowers wilt.
  • Storm fells. Blossoms blow away – and sometimes a grown tree comes down.

Only then does the gardener get a turn: plant one thing, build one thing, water one plant, harvest, or simply rest. The result lands on main as exactly one commit, with the weather in its title:

Day 3: An oak sapling on the little hill (rain 4.2 mm)
Day 2: Watering the young pine (sun 9.8 h)
Day 1: A pine sapling in the west of the garden (sun 10.6 h)
Day 0: An empty garden bed by a stream
GROW – Day 38: Watering the young pine Another grey, breezy day passes without a drop of rain, so the gardener fills a can at the rain barrel and waters the young pine by the sundial. Weather: Grey, grey 9.7 °C.
The garden on day 38 – straight from world/world.json.

Slow, and not up to us

A tree needs about a hundred stages to be fully grown. In Heilbronn that is roughly a year and a half of rain days. You cannot hurry it: watering adds a stage on a dry day, but only one, and only if the gardener chooses to spend the day on it. A dry summer will show in the garden. So will a wet one, and a cold snap in April.

Why this is worth watching

Because it is honest. Every change in the picture has a cause you can look up: this oak grew because it rained 12 mm on a Tuesday in May; that log is lying there because gusts of 72 km/h crossed the garden on the last day of July. The weather record is the garden's diary, and the logbook is its chronicle.

Everything that shapes it is open: the rules, the renderer, the prompt the routine follows (ROUTINE.md) and the complete history. The garden is transparently AI-maintained, and every daily commit says so.