Homemade Evapotranspiration Monitor

Want to know when it is time to water your garden without sticking your finger in the dirt every day?
Well, I did. So I set up some experiments using items I had lying around the place. It took me a few months the tune it up and finally came up with this. It takes into account evaporation due to wind, sun, and humidity. It also mimics the transpiration of plants and "reloads" automatically when there is rain, When it is empty it is time to water until the next rain. The hard part was finding the correct wicking material. I tried about eight different materials and came up with this. As often happens, simpler is better. Basically a catchment basin of non-porous material plus a "wick" of a material that will not corrode nor decay. (I am in zone 8B so don't have to worry about hard freezes cracking the terracotta.) Getting the ratio of the surface area of the basin to the exposed surface of the "wick" correct was the most difficult. The color value of the basin and the surrounding two foot radius surface also has minor effects on the rate of evaporation. The dog dish is 7 1/2 inches in diameter and 3 inches in depth. The terracotta pot is 4 inches in diameter and 4 inches tall. Granted, this limits the accuracy to three inches of rain. But then I am only concerned with "dry" spells. A deeper basin would also change the working aspects of basin to wick ratios. . I have found it to be very accurate and I have only begun to notice minor wilting of plants in the middle of the second day after the basin goes dry.
Commercial ET Monitors cost $400 to $1200, Mine cost $0.00!
Bob

Bob said  The hard part was finding the correct wicking material. I tried about eight different materials and came up with this

I find this idea fascinating.  The title sort of threw me since I don't know what an Evapotranspiration Monitor is.

Googling this was no help.

I have all the materials to make this.  Dog bowl, terra cotta pot.

Here is what I don't understand:  What is the wicking material?   Sand, dirt, potting soil?

Do I fill both pots with soil and then fill with water?  How much soil and how much water?

I find sticking my finger in the soil useless to monitor when I need to water as it is always dry except when I flood the garden bed.

Anne Miller wrote:

Bob said  The hard part was finding the correct wicking material. I tried about eight different materials and came up with this

I find this idea fascinating.  The title sort of threw me since I don't know what an Evapotranspiration Monitor is.

Googling this was no help.

I have all the materials to make this.  Dog bowl, terra cotta pot.

Here is what I don't understand:  What is the wicking material?   Sand, dirt, potting soil?

Do I fill both pots with soil and then fill with water?  How much soil and how much water?

I find sticking my finger in the soil useless to monitor when I need to water as it is always dry except when I flood the garden bed.

The terracotta pot is the wicking material. It wicks the water up where it is exposed to wind and sun and mimics the transpiration of water by plants.
Do not put anything in the bowl or pot. Wait for it to rain and then check each day to see when the bowl and pot are empty... then it is time to water until the next rain recharges the ET monitor. As long as there is water in the bowl your soil moisture is good. Remember, the sizes of the bowl and pot are critical.

Thank for the detailed explanation.

It rained a couple of nights ago, so I missed the window of opportunity.

At least I know how to do it when it rains again.

Thanks for the idea Bob, I know its a little late to reply but do you adjust watering when your trees begin to fruit. I have soil sensors and will add one of your sensors for visual verification. I was also thinking of adding a capacitive sensor onto the pot, and generate my own pet data. Cheers barney

Hi Barney
No, I do not irrigate my trees. They are all at least 25 years old and downhill from a large pond that is spring fed. They never suffer from lack of water. The evapotranspiration monitor is to monitor the annuals garden.