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Comment by KallDrexx | Hacker News Reader

Why do you need internet connectivity for any of that?

My sprinkler system has a sponge hooked up to the roof. If the sensor detects the sponge has too much moisture it doesn't turn the sprinklers on, because that means the soil is still saturated from recent rain.

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A forecast driven watering algorithm can look for rain in the immediate future, rather than the current state of the ground. It can also change the duration of watering based on temperature and relative humidity. RainMachine does that while only consuming weather data. You also have the option of turning that off and just using wireless control of the sprinklers, which as the GP says is extremely handy.

Is there a reason why the sensor is in a sponge on the roof rather than in the soil?

If it were in the soil, the sprinkler system would suppress itself in a feedback loop unless you had an intentional brown spot for the sensor.

How long is watering suppressed by the sponge? Does the controller "remember" that the sponge triggered a few days ago when the watering day comes around?

It has a permanent sensor on there, so the sensor doesn't remove the signal to not turn the automatic sprinklers on until you press the manual bypass button, or until the sensor no longer detects moisture above the set threshold.

When the controller hits the scheduled time it checks with the sensor unit, if the sensor says there's too much moisture it doesn't turn them on.

Nice, so it holds water just like the earth. Makes sense.

I wonder if that actually works that well. Especially with black roofing tiles which get quite hot. Compared to the hopefully shaded by the plants themselves soil. If your plants are sometimes shaded by trees depending on time of day the sponge will also probably fail you because your roof is more likely not to be shaded at all in many places for fear of overhanging tree limbs or roots being a danger to the house over the long term. Though it would be good for saving on cooling costs/energy use but then the sponge stays too wet vs. the soil.

I'd go for a soil moisture probe. That checks whether the plants really need the water, not whether a sponge with a "different reality" than the plants is dry.

Weather report data is cool though. Though you can't trust the weather report only, you can nicely combine the data from a soil probe (a "multi zone" system with a probe per zone would be great, probably easy to program with a Pi) with expected rain but an override via the soil probe if it actually didn't rain.

Since the OP said sprinkler I'm sort of thinking lawn though which I think should just never be watered at all ever. Waste of water just to look nice. And yes our town actually prohibits watering of lawns in summer. And for plants drip irrigation is better than sprinklers but hey, if you have a sprinkler system already go for it.

> I think should just never be watered at all ever

Depends on the situation. My town wants us to water less frequently, but keep our grass from drying out to prevent a fire hazard and soil erosion.

I do wish my front lawn was smaller to be sure. I'd be happier with more garden beds or garage/shed/workshop space.

Caveat: I don't live in a fire hazard zone so take this with a grain of salt.

Wouldn't it be better not to plant any grass if it's that bad where you are? For soil erosion planting something else sounds more adequate.

I do see a problem with septic fields. Can't plant anything else that I know of on those but grass. If you do know of something let me know and I'll plant it on mine instantly lol.

Why would you not plant a garden? I could maybe see not wanting to plant root vegetables, but peas, strawberries, cabbage, etc surely present no issues whatsoever. (And TBH, root vegetables should be just as fine if the septic tank is doing it’s job.)

From what I read about it, for three reasons:

    It's not entirely clear (some people/studies say it's fine, others say it's not) whether certain pathogens can end up in your vegetables this way and/or which vegetables would be fine and which wouldn't. I mean, some people do compost their own #2 and put it on their veggies and while it's been OK so far for many, I personally stay on the safer side of these things until desperate times call for such measures.

    Anything that has a root system that is able to reach the septic field's drain lines is potentially able to clog the holes. E.g. I tried raspberries in a planter on top of it for a while but even though I tried, I couldn't contain the roots and/or raspberries fall down and the seedlings grow in the grass. I ended up removing the whole thing just in case as septic drain field repairs are either expensive or a lot of work.

    Evaporation apparently plays some part in the effectiveness of the drain field (it doesn't just all drain out into the ground). Though I wonder, why plants taking up the water and evaporating it via their leaves wouldn't do the same thing, potentially even better through a larger surface area, so I guess it's mainly the first two points.

Well, anecdotally, I ate from a septic-fed garden for more than a decade, to no ill effect, from potatoes and carrots, to peas and broccoli. I wouldn’t hesitate to do it again. (But, yes, one does need to consider roots clogging the pipes; annuals perhaps safer than perennials, which surely drive roots deeper.j

Clover is a popular alternative. Some homes are xeriscaped (no lawn). But converting an existing lawn is expensive, even with subsidies. Selecting native grasses and watering less is an affordable compromise.

> I wonder if that actually works that well. Especially with black roofing tiles which get quite hot.

FWIW the sponge isn't literally on the roof. It's on a handle that's connected to the edge of the roof and holds it probably 4 or so inches horizontally away from the roof.

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