Soil moisture sensors: How do they work and why should I use them?

We’re often asked questions about our soil moisture sensors. Just what do they do, exactly? Why do I need a soil probe? Are they easy to use or just fancy gadgets for the techie crowd? The truth is, we think they’re a really user-friendly and practical addition to any gardener’s toolkit. So, if you’re not sure what the deal is with soil moisture sensors, here’s our quick and easy guide.

What are soil moisture sensors?

They’re essentially a probe that you push into the soil where you’re growing your plants to record the moisture conditions. It’s basically a more accurate way of determining how wet or dry the soil conditions are than the good old-fashioned prodding with a finger (although, if that works for you, carry on). They give gardeners a more comprehensive picture of what’s happening underground and when your plants need more, or less, water.

How do soil sensors work?

Since their invention, most plant watering sensors have measured soil moisture in one of two ways:

• by measuring the conductivity of the soil (sensor resistance increases when soil dries out and decreases when soil gets wetter)
• or by measuring the suction pressure at the tip of the probe (which gives an indication of how hard root have to work to extract water from the soil)

Both systems have their drawbacks in terms of accuracy and cost. That’s why many growers have moved towards using capacitance sensors. The capacitive soil moisture sensing probes we supply with our Harvst greenhouses are examples of this and ours measure soil temperature too. Here, measurements are gathered by recording how the soil reacts to an electrical field around the sensor. An accurate and cost-effective option for the average gardener.

What are the benefits of using a soil moisture sensor?

We love them. And for good reason. There are a wide range of benefits to using soil moisture probes – whether it’s in your greenhouse, garden or houseplant pots. For us, the main plus points are:

• Convenience – they just make life so much easier. The plants will effectively tell you when they need a drink – no guesswork. And when connected to a smart automated irrigation system like Watermate, you don’t even have to pick up a watering can.
• You grow stronger plants – plants’ water use varies as they grow so a sensor helps them get the exact amount of water they need as they develop. Some plants are particularly sensitive to changes in soil moisture and experiencing drought stress so by optimising the growing conditions you’re reducing the possibility of root disease problems and giving your crops the best chance of being healthy.
• You save water – we all want to save our precious natural resources (and reduce our water bills). With smart moisture monitoring, everything is fine-tuned, so it’s far more water efficient.
• They’re very helpful for new gardeners – knowing when to water, and how much, can be tricky for inexperienced gardeners to master. With a sensor you have so much more guidance to get things right.

I’m not much of a techie – are capacitance sensor systems hard to use?

No, not at all. It’s like anything else – once you’ve set things up for the first time, you’ll easily get to grips with how it all works and what the readings mean. The most important thing is to make sure the soil moisture probes are placed properly so that your readings will be as accurate as possible. If you’re using our Harvst sensors, we’ve done all the hard work for you – all you need to do is install the sensors in the soil, connect to the Harvst app and away you go.
And if you get stuck, we’re always happy to give you advice and talk you through things when you need a bit of extra help. Just ask. You can also find more about our capacitance sensors on our soil moisture sensing explainer page.

So, why not give soil moisture sensors a go? They’re user-friendly, help optimise growing conditions and make your life easier – win, win!