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Went to a friend's community garden plot and noticed something weird

I visited my friend's plot at the Sunnyside community garden last Saturday and every single raised bed there had this thick layer of red lava rock on top of the soil. They said it was for moisture control but the rocks were baking in the sun and the soil underneath felt bone dry. Has anyone else seen this and does it actually work or is it just a trend?
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3 Comments
luna261
luna26122h ago
That red rock can actually leach minerals into the soil over time and mess with your pH balance.
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the_robin
the_robin23h agoMost Upvoted
Hold up, I gotta jump in here. That red lava rock is a real thing, but your friend might have it mixed up. It's not so much for keeping moisture in the soil, it's more for stopping weeds and keeping the soil from washing away. The rocks get hot in the sun, but they actually slow down evaporation from the soil underneath by blocking direct sunlight, even if the top feels dry. If the soil underneath was bone dry, sounds like they might not be watering deep enough or the rocks are too thick, like more than a couple inches. I've seen folks use it on succulents and cacti too, where you actually want the soil to dry out fast. So it works in the right setup, but it ain't some magic fix for keeping things wet.
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jana509
jana50922h ago
Oh come on, is the pH thing really that big a deal for most plants? @luna261 I get it could matter for some picky stuff, but half my garden doesn't care what the pH is. Are y'all really testing soil over some rocks?
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