Soil moisture sensing
The Harvst smart garden system is fitted with sensors that detect the
capacitance
of
the soil, in other words how much the presence of the soil affects a small electric field
set up around the sensor. The water content of the soil will affect the capacitance;
wetter soil will be different from dry soil.
However, every type of soil is different. How tightly the soil is packed around the sensor
makes a difference, as do other things in the soil (such as fertilisers). For this reason,
there is no clear, consistent way to measure soil moisture in every location for every
user, so you’ll need to learn how your sensors are responding to your particular
situation.
Test your local soil
Get two samples of your local soil, or the compost that you’ll be planting in. Make one
of them wet, and dry the other one out to the point where you think “this really needs
water now”. These will be your two extremes.
Put one sensor in one pot, and the other sensor in the other pot. Wait a few hours for
data to come into your app, and you’ll see the two different moisture levels as a
reading out of ten.
As a starter, we recommend you set your “water when dry” regime to the level in the
dry pot (or one level up), so when the soil gets to that dryness, the watering comes on.
Set your “don’t water when wet” regime to the level in the wet pot (or one level
below).
Water moisture sensing is not a precise science, and takes time to learn properly. Be
patient and make controlled changes, and over a few days you will get a feel for how
your system works.
Don’t keep moving the sensors
Once you have placed your sensors in the soil, wait a few days to see a moisture
trend
line
on the chart on your app dashboard (this works far better on a computer screen
than a small phone). If you remove and replace the sensor, you’ll probably see spikes
and steps which confuse matters.
