---
title: Common haircap in a terrarium | Glass Jar Garden
description: Common haircap (Polytrichum commune): Tall upright stems like tiny pine trees. Wet, acid ground. Needs light 3,000 to 30,000 lux, humidity 60 to 100 % RH,...
url: https://glassjar.garden/guide/moss/polytrichum-commune/
---

Moss

# Common haircap
Polytrichum commune

Easy · Fine in a closed jar

Tall upright stems like tiny pine trees. Wet, acid ground.

## What the simulation uses

- Light: 3,000 to 30,000 lux (The brightness it grows well in.)

- Humidity: 60 to 100 % RH (Air moisture it is happy in; below the lower end it dries out.)

- Temperature: 5 to 25 °C (Comfortable range; outside it growth slows.)

- Dies at: below -30 or above 45 °C (Days beyond these temperatures kill it.)

- Soil pH: 3.8 to 5 pH (Soil acidity it prefers.)

- Grows up: 0.33 cm/month (How fast it gains height in good conditions.)

- Spreads: 0.06 cm/month (How fast its edge creeps outwards.)

- Thickens: 1.25 %/month (How fast its cover fills in on its own ground.)

- Copes with wet: good (How well it stands soggy soil; poor means rot comes quickly.)

- Copes with still air: fair (Sealed jars have still air; poor means grey mould finds it.)

- Copes with shade: fair (How well it holds on in dim light.)

- Copes with drying: fair (How well it survives the jar drying out.)

- Water use: 0.04 ml/cm²/day (Water that evaporates off the cushion each day in room air.)

- Holds water: 0.2 ml/cm² (Water a cm² of moss soaks up and keeps.)

- Grows on: soil (Where it can take hold and spread. Moss that cannot grow on stone thins out there.)

## Care

- Day length: 10 to 14 h

- Substrate: Wet

## What kills it

- drying out
- lime
- deep shade

## Description
This is the largest common moss, usually 5 to 10 cm tall and sometimes far more. It grows fast and may outgrow a small jar. Keep it wet, acid and out of deep shade, and never use lime.

Also called great golden maidenhair, haircap moss.

Estimated, where sources were thin: species growth rate (genus data used).

## Sources

- [en.wikipedia.org/wiki/Polytrichum_commune](https://en.wikipedia.org/wiki/Polytrichum_commune)
- [ohiomosslichen.org/moss-polytrichum-commune](https://www.ohiomosslichen.org/moss-polytrichum-commune/)
- [nora.nerc.ac.uk/id/eprint/1131/1/BRYOATT.pdf](https://nora.nerc.ac.uk/id/eprint/1131/1/BRYOATT.pdf)
- [digitalcommons.mtu.edu/cgi/viewcontent.cgi?article=1066&context=bryo-ecol-subchapters](https://digitalcommons.mtu.edu/cgi/viewcontent.cgi?article=1066&context=bryo-ecol-subchapters)
- [academic.oup.com/aob/article/94/4/593/211212](https://academic.oup.com/aob/article/94/4/593/211212)

[Grow it in a jar](https://glassjar.garden/?guide=moss/polytrichum-commune)

[Common feather-moss](https://glassjar.garden/guide/moss/kindbergia-praelonga/) · [Common pocket moss](https://glassjar.garden/guide/moss/fissidens-taxifolius/) · [All moss](https://glassjar.garden/guide/moss/)