My husband and I are very novice gardeners in Southern California (Hardiness Zone 10b). We’ve recently been working on one section of our (hillside) garden and realized that there was a greywater pipe already going into our soil from the two upstairs bathrooms of our house (done by previous onwers). Right now we believe it’s just a single pipe opening under the soil, but we figured we could hopefully utilize this to water a couple of trees – one a mature Pitis Porum and ideally a second new tree – preferably a Haas Avocado. The new Avocado would be in a separate part of the garden, around 12 feet downhill from the Pitius Porum.

My initial quesiton is this: We were advised by a local greywater enthusiast that we could easily water the two trees in the following way:

1. dig a 4 foot deep hole just uphill from each tree.
2. Fill it with Peat Moss
3. Place the pipe around 6” below the surface, emptying out into the Peat moss.
4. (A Y-pipe would divert the water, half to the upper slope Pitis, the other half down to the new avocado tree).

Thus our bathroom greywater would in theory water these two trees, with the Peat moss providing a steady (natural) reservoir, without having to go into complex greywater distribution/irrigation systems.

Any thoughts, advice or tips?

Many thanks,


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Hi Christine,

That sounds like a fun surprise that you already have the starts of a greywater system for your yard! And the plan you outlined sounds like a good start. I have a few suggestions.

  1. If you are able, I would assess how much water is coming out of the pipe and where it is coming from. One of you would be in the bathroom, the other out by the pipe. One would turn on a fixture and let it run for 30 seconds or so and turn it off. The outside person would wait to see if the water comes out. It may take a few minutes for the water to work its way outside, depending on how far away it is. And you’d do this for each fixture. Once you know where the water is coming from you could assess how much comes out based on your showering habit and shower head. And you may have enough water for more than 2 trees if you’re considering additional plantings.
  2. Do you know if there is a diverter valve in the shower drain to control the flow of water? I’m wondering if they may be build a real system and divided up the water to more place, or if they just ran a pipe outside. Having a diverter valve would indicate they had some knowledge of greywater and put in more effort than just one pipe, but this is just a guess.
  3. If you go with the 2 tree irrigation idea, I’d dig basins no more than 2 feet deep. Four feet is much too deep. You want to keep the water as high in the soil profile as you can, so it reaches more roots of the trees. It’s better to have wider basins to gain capacity than deeper ones. So, you’d dig a basin like a trench above the trees.
  4. I would use a “flow splitter” instead of a wye fitting. Flow splitters are called “double quarter bends” or “double ells” or “twin 90s”. If you can’t find one locally you can order on-line.
  5. Be sure to protect the outlet pipe with an irrigation valve box so it doesn’t get clogged up.
  6. Use mulch (arbor mulch/wood chips) instead of peat. Mulch is a local product and does a great job filtering greywater.

If you need more info, I wrote a how-to book called Greywater, Greenlandscape. It’s available from most libraries as well as for purchase as e-version or book.

Good luck with your system!


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