Donny Hooks of Cold Creek Nurseries is doing our overall landscape planning, with an emphasis of finding highly survivable, primarily native plantings to enhance our overall enjoyment of the property.
Of course, being highly survivable takes on new layers of meaning in an ultra-automated property.
One of our greatest challenges is in watering management, though not (as people commonly assume) for the purpose of reducing water consumption. With the emphasis on management, we want to let our automation assure that we neither over- nor under-water the plantings.
Because the last thing we want to do is to pay to replace them.
Like many irrigation approaches, we will have the usual electrically activated solenoid sprinkler heads deployed to the various zones where grass or trees or shrubs or gardens need water. Unlike most, our controllers will directly (well, through relays) trigger those heads. Nothing will be governed by timers. We will collect online weather micro-forecast data and have our own on-site weather instruments; those will be instrumental in determining when not to water.
Knowing when to water and how much to water is something that the soil should tell us. When soil moisture drops below early-alert or critical-alert levels, we can use rough estimates of the needs of each zone to determine a zone's watering duration, but we intend to be a little more tactical than that. The initial watering will be to perhaps two-thirds to three-quarters of that amount; after a delay of perhaps an hour (we will determine these things empirically after the landscaping is in) we will take another look at the soil moisture level.
Foiled by soil
The major constituents of the soil on our property are clay and sand. The clay components tend to shed or block water; the sand passes water right through; so what's the outcome?
In practical terms, Donny tells us, it's that he's never seen a soil moisture probe that he can trust. We, as you may guess, may take a stab at inventing one, and of getting some alternative probes in for Donny to try.
A literal underground radio station
About 50 years ago, two neighborhood guys experimented with metal stakes in the soil as a way of sending signals between their houses. One pair of stakes, a few yards apart, was driven by the speaker output of a reel-to-reel rape recorder. At the other end, another pair of stakes in the ground connected to high-impedance crystal earphones. That jury-rig worked.
We think we can adapt that idea. Rather than sending a modulated signal (as they did when playing the tape), we can use a continuous tone in an ultrasonic range, above human or pet hearing - perhaps something around 40,000 Hertz. If our transmission uses one deep ground post in the center surrounded by a large-diameter ring, the result should be a horizontally polarized omni-directional signal . Receivers in each watering zone can involve a simple field-effect transistor (high impedance) input to a tuned circuit (even coarsely tuned, to favor signals near 40 KHz); that should give us a Voltage level that we can digitize.
The irrigation sprinkler heads get connected with a 24-Volt AC power feed; we can easily add a shielded cable with two inner conductors, one for providing DC power to the receiver and the other for sending its digitized reading back to the irrigation controller.
While the signal path to a more distant zone may represent a complex challenge in determining the true endpoint soil moisture level, we are not on another planet. We can determine how the levels at zones adjacent to the transmitter relate to manual measurements on site, and run a series of tests to try to relate signal strength readings in each zone to the actual measured soil moisture content there. That will allow us to profile single zones in a way that will make it an easy interpretation for our controllers.
Remember, this is ultimately not about high precision; this is about being able to know for each zone (and whatever is planted within it) whether there is a desperate need for water, an urgent need, a modest need, no need, or (perhaps) if it has been over-watered - think of it as not so very many pips on a bar graph.
Other plant needs
Our horticultural expertise just ended when we spelled the word. While there may be no end of instrumentation to monitor other elements of the soil conditions or the health of the plantings, that expertise comes in the package when we engage a landscape service rather than trying to do everything ourselves.
Other elements of enjoyment
Of course there are - but Marty is going to stop for a Scotch (The Macallan, Sherry Oak Cask, 12-year-old) and a cigar (Rocky Patel) while he thinks about what they may turn out to be.
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