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.
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.)
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.
