Monitoring soil moisture

Someone asked on Stacy's podcast about a good way to monitor soil to know when to water.  So I was motivated to finish this and get it posted.

Real Options I've tried:

Davis Soil Moisture station
Expensive but works.
Pros:

• Prosumer grade gear. It still is working 7 years later with little maintenance. 
• You can expend to many units as the the consoles and hubs are coded to each other. 
• I've ran Davis on cables up to 100 feet with chewed wires and ants getting into the hub being the only issues and the hub upto over 50 feet from the gateway/console.
•  Leaf Wetness Sensors come with 40’ (12 m) of cable standard and can be extended up to 200’ (61m) using 6-conductor 26 AWG cable.
• Soil Moisture Sensors come with 15’ (4.6 m) of cable standard and can be extended up to 1000’ (300m) using #18 gauge UF cable.
• Temperature Sensors come with 15’ (4.6 m) of cable standard and can be extended up to 800’ (242m) using #24 AWG shielded cable or up to 1200’ (260m) using #22 AWG shielded cable.
• Sensors can be placed as deep as you want.
• Temperature reading is true at depth and unaffected by air temperature.

Cons:

• Sensors are wired to transmitter though this might be a plus too given only one solar charged battery is needed per 4 sensors.
• $466 to $600 for hub and 4 sensors pairs. Plus you need base / weather station for it to talk to plus more if you want it to upload to cloud services so another $500 - $1000 depending on models and features.

Ambient Weather WS-8482 $87
Probably best on a budget.
Pros:

• Way cheaper. Even with base plus 7 $29 soil moisture sensors still costs less than the Davis base unit with only 2 temp/moisture pairs. 
• Wireless sensors though that also means a battery for each.

Cons:

• Some of the sensors seems to not work all that well while others track closely to the Davis units. So might still be cheaper even if you have to toss some of the sensors but you might need to toss some.
• You are limited to 7 sensors total (plus station temp/humidity) or placing stations out of range of each other as only 7 radio channels. Some of my sensors are over 50 feet away so hard to say how far that separation might need to be.
• Hub needs to be indoors with AC power and WiFi so may not reach to some areas.
• Limited to reading about 8 inches down max since transmitter top needs to be above the ground.

Tried but failed:

Wireless Tags Water/Moisture Sensor and Plantlink both were completely worthless for more than telling when being watered. Neither seemed to last long either. The Wireless Tag you can not even change the batteries in.  Scotts bought Plantlink on 2016 then discontinued it. I appears they used the tech to create a new Scotts' version.  At $99 for a hub and one sensor then $40 for each add on sensor, it seems overpriced. Amazon reviews are NOT good either. Oddly those on their site generally are. That ought to give you pause right there.

Though Wireless Tags indoor sensors are great and damn cheap for what you get (temp, humidity, vibration, signal level, and battery level). Especially if you buy 5+ at a time. I even use them inside the freezer.

Also tried Wimoto SEN001 Sentry Bluetooth Smart Water Sensor, alos no longer available, a couple years back but those kept losing connection on top of the iffy data.

Compared:

Homeseer can link to Ambient and Davis via the Ambient site plugin.
Wireless Tag talks to Homeseer directly through REST api calls from the gateway.

Sample Ambient site screens of my Ambient Weather WS-8482. Note the Ambient site also works with Davis stations. Both also go to Wundergound site. When Wunderground is not having issues. Currently soil moisture is not showing there.

Monthly compares
Rain fall (not including from sprinklers)

A Davis sensor recorded (note only one seems to make it to the cloud)

Note the Davis sensor moisture data is sort of inverted as it really reports dryness.

An Ambient sensor about 6 inches away.

Just for grins here is the chart for the same period for the one Wireless Tag that is still "working".

The sun can really throw off the temp readings. The moisture setting had been adjusted to match a meter but quickly started to vary. Finally just left alone. Note this is outside in a pot and the spikes appear to be sprinkler times.

This is the matching Ambient sensor

Though if you are using Rachio to water an area (no pots) then checking the soil a few times with a cheap manual $10 meter to get it dialed end might make the soil monitoring unneeded since the Rachio takes weather and soil type into account and adjusts as needed.