Sustee Aquameter Review

Overview

Every other moisture tool in our round-up works the same basic way: insert a probe, get an immediate reading, remove it (or leave a WiFi sensor logging in the background). The Sustee Aquameter does something different. It’s designed to stay in the pot permanently — a slim stick with a cotton core that wicks moisture up from the soil to a small viewing window, which changes colour from white (dry) to blue (watered) as the core absorbs water.

There’s no dial, no number, no battery. You glance at the stick already sitting in the pot and read one of two states. That’s a genuinely different design philosophy from the XLUX, not a more expensive version of the same idea.

How It Actually Works

The mechanism is entirely passive: a core of natural, biodegradable material inside the plastic housing draws moisture up via capillary action, the same basic physics as a wick in a candle or a paper towel dipped in water. As the surrounding soil dries, the core dries with it and the colour reverts from blue back to white. No electronics, no galvanic reaction, nothing to charge or replace beyond the core itself.

Because the core has to take up or lose water before the colour changes, expect the indicator to lag the soil a little: it turns blue a while after watering, and can stay blue for a while after the topsoil itself has dried, since it’s reading moisture further down the pot. That lag is the trade-off for a reading you never have to take. Sustee sells it in small, medium, and large sizes to match pot sizes — the medium suits pots of roughly 9–18cm — and it’s designed and made in Japan.

Leave-In vs Insert-and-Read

This is the real comparison point against the XLUX, which we’ve also reviewed. The XLUX gives an instant, graduated reading (1–10) the moment you insert it, then comes back out — you use it as a spot-check tool, not a permanent fixture. The Sustee gives you exactly two states (needs water / doesn’t), but it’s always there, always visible, no action required to check it.

Which is better depends on what you actually want. If you like the ritual of checking pots — walking the collection with a probe, reading each one — the XLUX’s instant graduated feedback suits that better, and its 1–10 scale genuinely does tell you more (how wet, not just wet-or-not). If you want to glance at a shelf of plants and immediately see which ones need attention without touching anything, the Sustee’s always-visible colour signal does that better than any tool that has to be inserted first. For pots you don’t want repeatedly disturbed with an inserted probe — orchids in bark mix, anything with a fragile root system near the surface — leaving a single Sustee in place also avoids the repeated poking a dial probe involves.

Neither tool loses to the other in an absolute sense; they’re solving slightly different problems. Plenty of collections benefit from both: Sustee in the pots you check daily at a glance, XLUX for the occasional deeper diagnostic read.

Living With the Core Replacement

The one genuine maintenance point: Sustee recommends replacing the core every 6 to 9 months, after which the indicator becomes less reliable. Refill cores are sold separately, in sets, and swapping one is a matter of twisting off the cap and dropping in the new core. This isn’t a surprise defect — it’s inherent to a wicking mechanism, the same reason any cloth wick eventually needs replacing. Budget for it as a minor ongoing cost, not a one-off purchase.

Where It Falls Short

The binary signal is the honest limitation. If you want to know whether a pot is at 3/10 moisture or 6/10, the Sustee can’t tell you — it’s already blue at both of those points, provided the soil is above its “watered” threshold. For anyone who wants the nuance of a graduated scale, the XLUX (or the SONKIR 3-in-1 if you also want light and pH) does that job better.

The Verdict

The Sustee Aquameter earns its place not by beating the XLUX at the same job, but by doing a genuinely different one: a permanent, glanceable, no-action-required moisture indicator rather than a spot-check probe. For a collection where you want to see status at a glance rather than actively test each pot, it’s the right tool — and a reasonable companion to, not necessarily a replacement for, a dial probe like the XLUX. For methodology see how we review.

Sources

• Sustee (via IPPINKA): Sustee refills — blue/white indicator, 6–9 month core replacement, biodegradable core material, made in Japan, how to replace the core.
• Amazon UK: Sustee Aquameter, Medium, pack of 2 — UK price, medium size for 9–18cm pots.
• Prices checked October 2026.