moisture sensor, solenoid, 9v battery and arduino?

Thread Starter


Joined Apr 28, 2011
Hello, My dad has a small lemon tree at his house about 75 miles from where I live. He's having long term medical problems and isn't at the house, so I have to travel there once a week to water the tree. It's not a sensible situation. I have no experience with building an electronic project although I have done some reading about basics. I'm wondering if it is possible to build an automatic plant watering system with the following components. A controller (an arduino?) powered by a small (9v?) battery, a solenoid valve triggered by another small battery, and a moisture sensing probe. I'm hoping that the arduino could spend most of its time asleep (to extend the battery's life) and wake two or three times a day to take a reading from the moisture sensor. If the reading is below a set value then the arduino (or whatever controller is appropriate) would open the solenoid valve for a minute (allowing water to flow from a reservoir above the plant) then close it. The arduino would then go back to sleep.

It seems simple in theory, but I'm guessing. Thanks very much for any advice.



Joined Jan 15, 2015
I will venture a guess that if lemons grow there is little likelihood of an April freeze. Really in the interest of keeping things simple I would lay out a sprinkler hose around the tree and just turn the water on and off using a solenoid valve on a daily / weekly timer. Daily and weekly timers in all flavors can be had at your local Home Improvement store like Lowes or Home Depot. Really running a sprinkler hose for an hour or two doesn't use much water. Worst case it is raining while you water. The tree won't drown.

If you setup moisture probes depending on the soil they will corrode and become inaccurate. Spots in sun will not be uniform in moisture with spots in shade. You will need a power supply for the Arduino. When all is said and done it's easier to likely just buy a simple turn key solution.

Simple Irrigation Timers and most include the solenoid valve. There are likely battery versions.



Joined Sep 17, 2013
From what I've read the Arduino (don't recall which) draws about 34mA in sleep mode, so the average 9V battery won't last long :( . You might want to consider alternative microcontrollers, but an off-the-shelf timer/valve as Ron says seems the better bet.