Moss News Calculator

1. Enter the area your moss covers, in square metres.
2. Pick the moss type, which sets the base growth speed.
3. Set the moisture, shade and average temperature for the spot.
4. Read the yearly growth rate, plus estimated carbon capture and water retention.

The Moss News Calculator is a tool that estimates how quickly a patch of moss grows and the environmental benefits it provides. It combines the moss species with the moisture, shade and temperature of the site to produce a yearly growth rate, then adds rough figures for carbon capture and water retention.

It is built for gardeners, green-roof owners, students and anyone growing or studying moss. The growth rate is a solid planning estimate; the carbon and water figures are ballpark values, because real numbers vary widely with species, climate and how the moss is measured.

1. Start from the species base rate, from 1 mm a year for cushion moss up to 8 for sphagnum.
2. Apply the moisture factor, 0.2 plus moisture percent times 0.016, up to about 1.8 times.
3. Apply the shade factor, 0.3 plus shade percent times 0.012, up to about 1.5 times.
4. Apply a climate factor that rewards cooler average temperatures.

Carbon capture scales with the new growth and the area, while water retention uses the rule that moss can hold around 20 times its dry weight in water.

Take 10 square metres of feather moss in a shady, damp forest spot: 75 percent moisture, 70 percent shade and a cool 58 degrees Fahrenheit. The base rate of 3 mm is multiplied by a 1.4 moisture factor, a 1.14 shade factor and a 1.30 climate factor, giving about 6.2 mm of growth a year, or 3.1 cm over five years. That patch captures roughly 9 kg of CO2 a year and can hold around 160 litres of water.

Species

Species is the biggest lever. Fast, water-loving sphagnum can outgrow slow cushion moss several times over in the same spot.

Moisture and Shade

Moss has no true roots and dries out easily, so steady moisture and shade that slows evaporation both raise the growth rate sharply.

Temperature and Surface

Cool climates suit moss better than hot ones, and rough, slightly acidic surfaces hold moisture and anchor moss better than smooth glass or metal.

Moss behaves very differently from the plants people usually compare it to.

Where grass fails in deep shade, moss often thrives, which is why many gardeners stop fighting it and grow it on purpose.

Planning a Moss Garden or Wall

Estimate how long a patch takes to fill in before you plant or transplant.

Green Roofs and Carbon

Get a rough idea of the carbon and water benefits a moss roof might provide.

Study and Curiosity

See how species and conditions change growth for a project or just to understand what moss needs.

1. Too Much Sun

Most moss scorches in full sun. Match the species to the light or add shade.

2. Letting It Dry Out

Moss growth stalls when it dries. It survives dormant but only grows when moist.

3. Rich Soil and Fertiliser

Moss prefers poor, acidic conditions; feeding it often helps weeds instead.

4. Treating Estimates as Exact

Real growth, carbon and water vary widely, so use these figures as a guide.

The growth rate follows a clear, documented model and is a good planning estimate. The carbon and water figures are simplified and should be read as ballpark values.

Most moss grows slowly, from about 1 mm a year for dense cushion moss to several millimetres for feather moss and much more for sphagnum in wet, shady, cool conditions.

Moss grows best with steady moisture, shade, cool temperatures and a rough, slightly acidic surface. Sun and dryness are its main enemies.

Yes, moss takes up carbon dioxide as it grows, and peat-forming sphagnum stores large amounts over time. The figure here is a rough estimate, not a measured value.

Moss can hold roughly 20 times its dry weight in water, which is why moss and peat are prized for retaining moisture in gardens and green roofs.

Sphagnum moss grows fastest in wet, cool, shaded conditions, while cushion moss is the slowest and densest.

Yes. Mat and cushion mosses grow on rock and roofing given enough moisture and shade, and are used on green roofs for insulation and water capture.

The usual causes are too much sun, drying out, or rich soil. Moss needs shade, steady moisture and poor, acidic conditions.

No. Those figures are simplified estimates that vary widely by species, climate and measurement method, so use them as a guide only.

No. The calculator runs entirely in your browser and nothing you enter is stored or sent anywhere.

• What moss is and how it grows (Wikipedia).
• Sphagnum and peat moss (Wikipedia).
• Moss on green roofs (Wikipedia).