Hydrometers for Watering Plants

Written by brian coughlin
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Hydrometers for Watering Plants
Proper watering is important for optimal plant growth. (Comstock Images/Comstock/Getty Images)

Hydrometers are devices that measure the amount of moisture in the soil. They work by inserting a probe, either attached directly to the meter body, or on a cord. This probe uses a tiny electrical current to test how moist the soil is. This can help you to determine how much and how often you should water your plants. There are several types of hydrometers available, each with advantages and disadvantages.

Types of Meter Probes

Meter probes are grouped into two types, integral and detachable. Integral probes are built directly into the meter body and cannot be detached. These are generally used for "quick" checks in houseplants and yards. Detachable probes are attached by a wire to the meter body, allowing you to reach over your head, or under a bush to insert the probe, while still allowing you to be at eye level with the meter.

Types of Readings

Some units use a needle-type meter, which shows a pointer against a dial. The dial may be marked from "wet, moist to dry" or a more general "safe/danger" or markings from 1 to 10. Others show a digital readout, which may be a "bar" (lit and unlit segments), or an actual number or series of numbers, that show you a range of possible moistures. All of them are methods to tell whether you need more moisture in your plants.

Types of Monitoring

There are two main types of monitoring probes; constant and meter. The meter type is designed to give you a reading at the time you test for it; then you clean it and put it away. They are not designed to be left inserted in the soil, and will quickly corrode, and be ruined, if you leave them there. The constant type is usually used with a remote or wireless receiver, which gives a continuous reading on the actual or relative moisture of the soil. Many of these more advanced devices also include temperatures. The probe bodies are often made of brass or other corrosion-resistant metals. It is essential that all hydrometers, no matter what type of material they are made from, are cleaned after each use. This will prevent corrosion.

Other Types of Constant Monitors

There are a few other types of constant monitors that are used mostly for potted plants. They may look like little birds, a plastic blob that blinks, a plastic flower whose centre changes colour when the soil is dry or a number of other shapes. The elements that tie them together, is that they all poke into the soil at least 4 inches and they all change appearance, in some way, to show you it's time to water.

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