---
title: Juniper haircap in a terrarium | Glass Jar Garden
description: Juniper haircap (Polytrichum juniperinum): Grey-green shoots with red tips that open like stars. Needs light 6,000 to 50,000 lux, humidity 40 to 85 % RH,...
url: https://glassjar.garden/guide/moss/polytrichum-juniperinum/
---

Moss

# Juniper haircap
Polytrichum juniperinum

Moderate · Open jar only

Grey-green shoots with red tips that open like stars.

## What the simulation uses

- Light: 6,000 to 50,000 lux (The brightness it grows well in.)

- Humidity: 40 to 85 % RH (Air moisture it is happy in; below the lower end it dries out.)

- Temperature: 5 to 28 °C (Comfortable range; outside it growth slows.)

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

- Soil pH: 4 to 5.5 pH (Soil acidity it prefers.)

- Grows up: 0.2 cm/month (How fast it gains height in good conditions.)

- Spreads: 0.05 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: fair (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: poor (How well it holds on in dim light.)

- Copes with drying: good (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, stone (Where it can take hold and spread. Moss that cannot grow on stone thins out there.)

## Care

- Day length: 10 to 14 h

- Substrate: Moist

## What kills it

- low light
- sealed jar
- lime

## Description
In the wild it grows on dry, acid, open ground, and its leaves are built to use strong light. Low light, lime and a sealed jar all hurt it, so grow it in an open container in a bright spot.

Also called star moss (trade), juniper haircap moss.

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

## Sources

- [en.wikipedia.org/wiki/Polytrichum_juniperinum](https://en.wikipedia.org/wiki/Polytrichum_juniperinum)
- [ohiomosslichen.org/moss-polytrichum-juniperinum](https://www.ohiomosslichen.org/moss-polytrichum-juniperinum/)
- [nora.nerc.ac.uk/id/eprint/1131/1/BRYOATT.pdf](https://nora.nerc.ac.uk/id/eprint/1131/1/BRYOATT.pdf)
- [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-juniperinum)

[Java moss](https://glassjar.garden/guide/moss/taxiphyllum-barbieri/) · [Knight's plume moss](https://glassjar.garden/guide/moss/ptilium-crista-castrensis/) · [All moss](https://glassjar.garden/guide/moss/)