---
title: How the terrarium simulator works | Glass Jar Garden
description: Every mechanism in the terrarium simulator in a few lines: health, hazards, soil, water, humidity, light, temperature, plants, moss, critters, mould and care.
url: https://glassjar.garden/guide/how-it-works/
---

Guide

# How it works
What the simulation does each day, one mechanism at a time, with the numbers it runs on.

- [Needs and health: Each day every living thing scores its needs; health follows the score.](https://glassjar.garden/guide/how-it-works/needs-and-health/)
- [Death and hazards: Only hazards kill, each rising from zero at its threshold.](https://glassjar.garden/guide/how-it-works/death-and-hazards/)
- [Soil: Layers drain, hold water, feed plants and set the pH the roots feel.](https://glassjar.garden/guide/how-it-works/soil/)
- [Water: Soil fills to what it can hold; the rest drains to the drainage layer.](https://glassjar.garden/guide/how-it-works/water/)
- [Humidity and the lid: Sealed jars keep every drop; open jars lose water to the room.](https://glassjar.garden/guide/how-it-works/humidity-and-the-lid/)
- [Light: The day's light, brightness times hours, drives growth.](https://glassjar.garden/guide/how-it-works/light/)
- [Temperature: The jar follows the room, a little warmer under a lamp.](https://glassjar.garden/guide/how-it-works/temperature/)
- [Plants: Plants grow on light and food, share space, and stop at the lid.](https://glassjar.garden/guide/how-it-works/plants/)
- [Moss: Moss creeps from its edges in damp air and browns back when dry.](https://glassjar.garden/guide/how-it-works/moss/)
- [Critters: Each crew is a colony that grows to what the jar can feed.](https://glassjar.garden/guide/how-it-works/critters/)
- [Mould: White mould blooms on fresh organics and leaves; springtails eat it.](https://glassjar.garden/guide/how-it-works/mould/)
- [Care: Mist, water, vent and tidy, by hand or on a routine.](https://glassjar.garden/guide/how-it-works/care/)
- [Chance and forecasts: Two things are random; everything else repeats exactly.](https://glassjar.garden/guide/how-it-works/chance-and-forecasts/)
- [Checked against real jars: Fourteen jars their owners described online, rebuilt and run: all fourteen turn out the way the real ones did.](https://glassjar.garden/guide/how-it-works/checked-against-real-jars/)