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Anatomy of a Thirsty Light
Thirsty Light Moisture Signal Chart

For Happy, Healthy Plants

Improper watering kills or injures houseplants more than any other cause. Overwatering is just as harmful to your plants as under-watering. The Thirsty Light® is designed to help you monitor your plant’s moisture so that you know when it’s time to water. It can be used in two ways:

Leave-In Method

Use one Thirsty Light® for each plant, leaving it in the soil. It is the most convenient way to use the Thirsty Light® because the plant’s soil moisture level is constantly monitored.

(Please note: the Leave-In method is extremely demanding on battery power and may shorten the battery life to as little as one week)

Quick Check Method

Share one Thirsty Light® among several plants, moving the probe from one plant to the next. The digital sensor tests conditions once every second, so each pot’s soil moisture can be assessed quickly and accurately.

How To Use the Thirsty Light®

Turn the power switch to the "ON" position. The Thirsty Light's LED alert light will emit a single long blink.

  1. Insert the Thirsty Light® into the soil so the pod and approximately 1" of the probe is above the soil line. Choose a location between the edge of the pot and the plant stem with good visibility of the LED alert.
  2. The LED alert blinks to tell you how moist or how dry the soil is (see Moisture Signal Chart). It blinks faster as the soil gets drier.
  3. Leave-In Method: Leave the Thirsty Light® in the soil with the power switch in the "ON" position. The LED alert will notify you when it's time to water again. Pay attention – you may need to adjust the probe (see Adjusting Performance section).

    (Please note: the Leave-In method is extremely demanding on battery power and may shorten the battery life to as little as one week)

  4. Quick Check Method: When you are finished checking the soil and watering, turn the power switch clockwise to the "OFF" position to prolong battery life.

Adjusting Performance

It is easy to fine-tune the function of the Thirsty Light® to match a specific plant's moisture needs. Soil dries from the top down, so the depth of the sensor affects the timing of alerts. If the plant is wilting from lack of moisture between waterings, choose a new location and insert the probe only 2"-3" deep in the soil. If the Thirsty Light® is alerting too soon, push the probe deeper into the soil. Do not allow the pod to come in contact with the soil.

Caring For The Thirsty Light®


  • While the Thirsty Light® is water resistant, avoid immersing the pod.
  • When watering, be careful not to pour water directly over the pod.
  • The probe is made of brass for maximum product life. A change in the surface color (patina) will develop after contact with soil and water. This patina helps protect the brass from corrosion and will not affect the sensitivity of the device.
  • If the Leave-In method is used, the probe may collect mineral deposits over time. Periodic wiping with a moist cloth and then drying will remedy the problem.


  • The probe requires good contact with soil for the Drypoint™ technology to work accurately. Therefore, the Thirsty Light® is not recommended for coarse/sandy soils or orchid mix.
  • Be sure the soil is firm around the probe of the Thirsty Light®, as loose soil may result in a false "dry" reading. Do not wiggle the probe after it is inserted, which will loosen the soil.
  • Excess amount of dissolved fertilizer can result in a false "wet" reading, when the soil is actually dry. See the Adjusting Performance section for help.

Battery Guide

The Thirsty Light® uses two standard 1.5V AG13 batteries.

Testing the batteries

Turn the Thirsty Light® "OFF" and then back "ON" immediately. If one long blink is emitted, the batteries are adequately charged. If a triple blink and long pause is emitted, or if there is no blinking, replace the batteries.

Changing the batteries

Insert batteries as shown

  1. Remove the screw holding the battery cover and set aside. Insert the tip of the screwdriver under the ridge just below the cover screw hold to lift the cover off.
  2. Remove the old batteries. Install new batteries with the polarities oriented as shown.
  3. Replace the battery cover by inserting the tab in the slot at the top of the opening, then snapping the bottom of the cover into place.
  4. Replace the cover screw and tighten.
  5. Verify the batteries are properly installed by turning the power switch to "ON". The LED alert signal should emit one long blink.

Helpful Watering Hints

Here are some helpful watering hints for the best results with potted plants:

  • Pour water evenly over the surface of the soil until it comes out of the drainage holes.
  • Avoid using softened water.
  • Don’t allow plants to sit in standing water for more than an hour.
  • Potted houseplants should always have good drainage. Occasionally the pot's drainage hole can become clogged by roots. Check the hole by pushing a stick or pencil into it.
  • A plant in an unglazed pot will need watering more often than a plant grown in a plastic or glazed pot, as water evaporates through unglazed pot surfaces.
  • Plants require less water in the winter or dormant months.