Comparing growing media for Drosera capensis

Why this question

Peat is the default base for carnivorous plant media, but peat extraction damages the bogs wild carnivorous plants live in, and growers increasingly ask whether peat-free alternatives work. Grower reports are mixed. A small, controlled comparison in one person’s conditions cannot settle the question, but it can show whether a difference is large enough to matter at home.

Drosera capensis is the test plant because it is cheap, fast-growing, tolerant, and easy to replace, so a failed medium costs little.

Hypothesis

Plants in the peat and perlite mix and in long-fibre sphagnum will grow similarly. Plants in the coir mix will grow less well unless the coir is thoroughly rinsed, because coir can carry residual salts.

This is written down before the trial so that the outcome can be compared with what was expected, whatever it turns out to be.

Setup and conditions

• Plants: nine Drosera capensis of the typical form, as similar in size as possible, ideally divisions or seedlings from the same parent so that genetic variation is small. Each is photographed and its longest leaf measured on day 0.
• Groups: three plants per medium.
  • Group A: sphagnum peat moss and perlite, 1:1 by volume.
  • Group B: long-fibre sphagnum moss, rehydrated and lightly packed.
  • Group C: coir and perlite, 1:1 by volume, with the coir rinsed in pure water until the run-off reads under 50 parts per million total dissolved solids.
• Pots: identical plastic pots, 9 cm (3.5 in), one plant per pot, labelled A1 to C3.
• Position: all nine pots in one tray, in the same position under the same light, rotated weekly so that no pot keeps the same place.
• Water: shared tray of rainwater or reverse-osmosis water, kept at about 1 cm (0.4 in). Because the tray is shared, any difference between groups comes from the medium, not from watering.
• Duration: one growing season, roughly April to September in the northern hemisphere, or 20 weeks.

Measurements

Every two weeks, for each plant:

• Number of living leaves with dew.
• Length of the longest leaf, in millimetres.
• A photograph from a fixed position.
• Any notes on colour, flowering or problems.

At the end: total leaf count, longest leaf, and a subjective health rating from 1 to 5 recorded before looking at the group label.

Controls and what is not controlled

The shared tray and shared position control water and light. Not controlled: differences between individual plants, small differences in how tightly each medium is packed, and the fact that one grower’s coir is not another’s. With three plants per group, only a large difference would be meaningful.

Updates

No updates. This protocol has not been started; the section exists to show where dated entries would go. When an experiment is running, each update is a third-level heading with its date, newest at the bottom:

2026-01-01 — Example of an update heading

A dated entry would describe what was observed on that date, in the same action and observation style as the growing log article.

Results

None. This is a planned example and no plants have been set up.

Limitations

• Three plants per group is a very small sample, so results would be suggestive at best.
• One season in one location says nothing about long-term performance or other climates.
• Coir quality varies between suppliers, so a result would apply to the batch tested.
• The health rating is subjective even when recorded blind.

Next steps

If run, the obvious follow-ups would be a second season with the same plants to see whether media break down differently over time, and the same comparison with a less tolerant species.