Arduino based soil moisture sensors for sprinkler zone override

Using Arduino Project Guidance
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Hello,

I have an automatic drip/soaker irrigation system for my vegetable garden, and I am starting to see a problem that I think I can solve with Arduino. I am a tinkerer and can follow directions, but I am NOT a programmer. The issue is I have a Toro ECT XTRA controller with 10 zones. It has the external wireless weather/rain sensor (which automatically increases/decreases watering time based on temperature and sun exposure), but I have vegetable beds and containers in various places that get varying amounts of sun.

I am finding that the beds that are shaded for part of the day are getting way overwatered, even after cutting down their watering times - and our weather has been kind of wonky, 96 degrees yesterday, 73 today with some rain, 75 tomorrow, 101 Tuesday.. The automatic compensator averages over a week, so right now it's watering at 120% - even though it's not as hot as it's been.. So I can't just set them on a different program with alternating days, because if it gets really hot they will dry out. The rain sensor is set to trip at 1/4", but I find that it dries out too fast and resumes the schedule while the ground is still wet. I also can't really set a manual 24 hour rain delay, because that overrides all zones and the containers will start to dry out.

So here's what I'd like to do. I don't want to build an entire new controller or use OpenSprinkler just yet. And all the Arduino projects I've seen using moisture sensors are made to activate pumps and such. What I want to do is use a moisture sensor (or two averaged) per bed to simply activate a relay to bypass that zone while it is too wet. The timer will still run its schedule but any zone with a sensor above threshold will not open its valve.

Ideally each sensor would be wireless (I could do battery or solar), with a single receiver on the Arduino that would be placed near the timer/relay board. It would not be a huge issue to wire everything though, I have outdoor Cat5, and the longest run would be about 100ft. A pair of Arduinos (one outside that connects to all the sensors, and one inside that connects to the relay board) connected by a single cable would be great too if that's possible.

Is this a realistic project? The hardware part is absolutely no problem for me but I would need some hand holding to write the program..

Thanks in advance!

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The unrealistic part is expecting consistent results from soil moisture sensors. The simple sensors will be corroded away to nothing in a week, the medium sensors won't last a year and complex ones, well now you are talking real dollars.

Find a sensor with the endurance you require, then work out how to drive that with an Arduino. Determine your power requirements for the sensor, Arduino and radio, then pick a solar cell and battery. Then work out how to put it all into a box that will survive out in the elements.

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MorganS:
The unrealistic part is expecting consistent results from soil moisture sensors. The simple sensors will be corroded away to nothing in a week,

That's if you put a voltage on them constantly. If you only measure for a few ms every 10 mins or so also the cheap ones can last for a while, too.
Still they're not all too reliable, so you have to check on them regularly.
Otherwise, I don't see any real obstacles in building a project like this.

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