Measuring soil moisture: when should you water?

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Why the finger test fails when you measure soil moisture

If you measure soil moisture with your finger, you only feel the top layer: the top 2 to 3 cm of potting soil always dries out first. Further down, at the roots, the soil can stay wet for days. If you water by feel, you give too much water one time and too little the next. According to the University of Connecticut, this switching between too dry and too wet is perhaps the biggest cause of dead houseplants. In a British survey of 2,000 adults, too much water (48%) and too little water (41%) were mentioned almost equally often.

A moisture meter measures where it matters: at the roots. That way you water based on what is happening in the pot, not on a fixed day. Then water thoroughly in one go until it runs out of the bottom of the pot, and empty the saucer within an hour.

Measure soil moisture: how to read the result by type of meter

Every meter shows the result differently. First check which type you have:

• Moisture indicator, such as the Seramis: blue means enough moisture, red means it is time to water.
• Meter with a 1–10 scale, such as the digital moisture meter (Rapitest 1825): compare the reading with the guide number for your plant group in the table below.
• Meter in percentages, such as the Soil Moisture Meter Pro and the Ecowitt WH52: use the table per soil type further down.
• Other meters, such as the 4-in-1 soil tester: follow the scale in the manual. You can find it under download manuals.

Guide numbers for the digital moisture meter (scale 1–10)

Plant type	Water at	Recognise by	Examples
Drought-loving	1–3	Thick, fleshy or leathery leaves	Orchid, snake plant, cactus
Average	4	Ordinary green leaves, not very thick or thin	Monstera, pothos, ficus
Moisture-loving	6–8	Lots of thin, soft leaves	Ferns, dracaena, peace lily

Vegetables, garden plants and lawn (digital moisture meter, scale 1–10)

Garden	Water at
Beans, peas, carrots, onions, peppers, potatoes, radishes	2–3
Tomatoes, lettuce, spinach, cabbage, cucumber, courgette, beetroot	3–4
Celery; roses, rhododendron, azalea, dahlia, fuchsia	4–5
Lawn, measured at a depth of 7.5 cm	5 = enough water

Measuring in percentages?

Digital and wireless meters such as the Soil Moisture Meter Pro and the Ecowitt WH52 show a moisture percentage. What is right depends strongly on your soil type:

Soil type	Water at	Max. retained	Wilting point
Sandy soil	± 13%	16%	7%
Sandy loam	± 17%	21%	9%
Loam	± 22%	27%	12%
Light clay	± 25%	29%	18%

How to measure soil moisture in 4 steps

1. Insert the meter halfway between the rim and the stem, to half or two thirds of the pot depth. In pots wider than 30 cm, measure closer to the stem. In the lawn, measure at a depth of 7.5 cm.
2. Wait a few seconds until the reading is stable.
3. Measure at least twice, at different spots in large pots and borders.
4. Wipe the probe clean and do not leave a probe meter in the pot; the probe can corrode and will then measure less accurately.

Moisture indicator, digital or WiFi: which moisture meter suits you?

	Moisture indicator	Digital meter	WiFi sensor
Reading	Colour: blue is fine, red means water	Number or percentage on the display	Percentage in the app, continuous
Battery	No	Yes	Yes, plus gateway
Stays in the pot	Yes, about one year	No, you measure when you want	Yes
Suitable for	A few houseplants	Many plants, vegetable garden	Greenhouse, vegetable garden, on holiday
Example	Seramis moisture indicator	4-in-1 soil tester, digital moisture meter	Ecowitt WH52 + gateway

For the vegetable garden, the lawn or large container plants, the Soil Moisture Meter Pro with a 28 cm probe is the best choice. If you want a meter that simply stays in the pot, choose the Seramis moisture indicator: it changes from blue to red as soon as it is time to water.

Our recommendations to measure soil moisture

Frequently asked questions: measure soil moisture with a meter

How it works and what the values mean

How does a soil moisture meter work?

The probes measure how well the soil conducts electricity. Wet soil conducts better than dry soil, and the meter converts this into a number or percentage. Simple meters with a needle therefore work without a battery; meters with a display or app do need one.

How do you use a soil moisture meter?

Push the probe into the soil halfway between the rim and the stem, to half or two thirds of the pot depth. Wait until the reading is stable, measure in at least two places and compare the result with the guide number for your plant or the table per soil type.

What is a good soil moisture reading?

It differs per meter. A moisture indicator such as Seramis is blue when there is enough moisture and red when you need to water. On the digital moisture meter with a 1–10 scale, water drought-loving plants at 1–3, most houseplants at 4 and moisture-loving plants at 6–8. If your meter measures in percentages, see the table per soil type. For other meters, follow the manual.

What moisture percentage is good?

That depends on your meter and your soil type. In garden soil, water at about 13% on sand, 17% on sandy loam, 22% on loam and 25% on light clay. Potting soil holds much more water, so different values apply there; follow the manual of your meter.

How do I know if my plant gets too much or too little water?

With too little water, leaves become limp, dry and brown at the edges, and the soil feels light. With too much water, leaves turn yellow and limp while the soil is wet, sometimes with a musty smell. Because the signs look alike, only a measurement at the roots gives certainty.

Accuracy and everyday use

Are soil moisture meters accurate?

A moisture meter for home use gives a good indication, not an exact measurement. It measures conductivity, so a lot of fertiliser or salt in the soil gives a reading that is too high. Always measure in two or more places. For accurate percentages, choose a professional meter such as the Soil Moisture Meter Pro or a sensor with an app.

Are soil moisture meters worth it?

Yes, especially for larger pots and in the garden. The finger test only checks the top few centimetres, while the roots may still be wet or already dry. A meter shows the situation where the plant takes up water, which helps you avoid switching between too wet and too dry.

How do you calibrate a soil moisture meter?

Most moisture meters for plants cannot be calibrated. You can check them, though: in the air the meter should show the lowest reading, in a glass of water the highest. If it does not, clean the probe. Sensors with an app sometimes let you set a correction; check the manual.

Can I leave the moisture meter in the pot?

Not a probe meter: the probe can corrode and will then measure less accurately. A moisture indicator such as Seramis or a wireless sensor is made to stay in the pot.

Is there a soil moisture meter with an app or for Home Assistant?

Yes. A wireless sensor such as the Ecowitt WH52 sends moisture, temperature and EC via a WiFi gateway to an app, and you get a notification when it gets too dry. Home Assistant has an official Ecowitt integration, but it does not support every gateway and sensor. Feel free to ask us which combination suits your system.

More questions about watering? See the watering FAQ.

Sources

• Luster Leaf, Rapitest Moisture Meter No. 1825 manual: guide numbers per plant and measuring depth
• Shortridge & Porter (2021), Scheduling Agricultural Irrigation Based on Soil Moisture Content, Virginia Cooperative Extension: field capacity per soil type
• FYTA, How do we analyze water: saturation of potting soil and garden soil
• University of Connecticut, Watering Houseplants: watering thoroughly and emptying the saucer
• University of Connecticut, Ailing Houseplants: irregular watering as the main cause
• Yorkshire Post (2022), Miracle-Gro/OnePoll survey of 2,000 adults: causes of dead houseplants

Last updated: 26 October 2026