subterranean homewatering blue

March 15, 2007 9:57 PM

how do I irrigate a new lawn subterraneanly?

This is for a small area (maybe about 8 m2), so I'm doing it myself. I want to use subterranean irrigation because as I understand it it uses much less water (no evaporation losses) and is neater, almost invisible.

Plan A was to use a weeper hose - one of those furry looking hoses that weep from the entire length - and wind it round the whole patch. But wont roots grow into that and block it up?

How about using a pvc pipe with regularly spaced holes in it? It's not flexible so would require joints - how far apart should the runs be? And wont roots and soil still block the holes up?

Has anyone done this previously?

posted by wilful to home & garden (8 comments total)

Grass doesn't grow especially well in swamps, rice paddies, or other natural environments where water rises from the ground. The canonical home of grasses are steppes or plains, where the water, such as it is, comes from above, and evolution has strongly selected for grass plants that do well in such places. Tens upon tens of thousands of square miles, on several continents, bear me out. Golf courses across America are based on water coming from above. Lush residential grass just takes fertilzer, sun, water (from above), reasonable drainage and time.

Subterranean water systems have all the problems you mention and more. They are a magnet for insects. They make arranging drainage more difficult. They don't deliver water evenly, unless their distribution arms are very close together. They're largely adapted to desert environments, where the soils and sub-soils they irrigate are extremely sandy, and the evaporative loss rates are incredible. They are ineffective at dissolving nutrients from common surface pellet fertilizer and at providing the leaf moisture preparation for particle clinging herbicide systems.

But you live in Austrailia. What do I know?
posted by paulsc at 10:24 PM on March 15, 2007

Your lawn could be on the cutting edge.
posted by artdrectr at 10:24 PM on March 15, 2007

I don't know of a subterranean watering system that isn't subject to root clogging, in the long term. Roots are very good at finding their way upstream.

Evaporation losses from surface watering will be low if you water deeply enough that water only just starts to run off, only just often enough to keep it green, and only do it at night.

Surface drip watering is way more efficient than sprinklers for trees, shrubs and vines, but properly-employed sprinklers are about the best you can do for lawns. Which is why low-water-use gardens generally don't feature much in the way of lawns.

If you want an invisible clog-proof system that doesn't involve sprinklers and doesn't use up drinking water, you can build a small flood-irrigation bed and keep it damp with greywater:

Hire a dingo digger or bobcat to scrape the topsoil off the lawn area to a depth of about 300-450mm. If your subsoil is sandy, get in a load of heavy clay (one cubic metre should be enough for eight square metres of lawn) and spread that over the existing subsoil. Next, compact it. Ideally, you want your subsoil to form an even, gentle, relatively water-impervious slope with no pooling spots; if you run a flood along the highest edge, you want it to run across to the other side as evenly as possible. Also ideally, the highest edge will be one of the long edges, and will be close to your house.

If your topsoil isn't already sandy, mix a load of sand into it to give it some porosity, or put it somewhere else and get in a load of sandy loam. Spread the topsoil back over the shaped and compacted subsoil, trying not to compact the topsoil, and seed it.

Run a trench into the topsoil along the uphill side, being careful not to go all the way through the clay layer if you've added one, and fill it with pinebark or shredded eucalyptus mulch.

Now divert the greywater outlet from your shower recess and bath into the trench. Don't use washing machine, kitchen sink or dishwasher drainage for this, because the salts and/or gunk content will be too high. Bath and shower water is usually pretty safe.

The outfall should be inside a large upturned flower pot halfway along the trench, and be at least 50mm away from the soil; that will stop roots finding their way back up the pipe.

Personally I think watering a lawn is a criminal waste of water that would be far better used to keep fruit trees healthy, but if you're going to do it, that's the way to do it.
posted by flabdablet at 10:59 PM on March 15, 2007

I want to use subterranean irrigation because as I understand it it uses much less water (no evaporation losses) and is neater, almost invisible.

If your aim is to minimize water use, then the best you can probably do for a patch of lawn is simply pre-dawn watering, to avoid evaporation. With only 8m2 you should be able to cover it with a single sprinkler head. Get it on a timer, set to run 2 hours before sunrise. Give it a fairly generous (as generous as you can afford) watering once a week - try to avoid watering more often, as large, infrequent watering should encourage deeper root growth. Watch the run-off though - if you're watering it so much that water starts running off, then it's time to cut back, obviously.
posted by Jimbob at 11:31 PM on March 15, 2007

I'd look at alternative methods. The main ways that grass gets dehydrated are by direct sunshine and by trees or shrubs. Aerating the grass every once in awhile helps the roots to grow deeper to damper soil.

Alternatively you could build a drain tile reservoir system underneath the soil and recharge that when the lawn gets dry. Building one is simple and low-tech, you can use thick mil plastic. The only problem with that is unless you plan it thoroughly, you could end up with some soggy spots after a rain event.
posted by JJ86 at 5:33 AM on March 16, 2007

Go with the predawn watering and while you're at it, set it up to run from gray water from a washing machine or your bathtub if you can.
posted by plinth at 5:54 AM on March 16, 2007

Grey water is best not applied via sprinklers or any other device with small holes; it works much better for flood/seep irrigation than for sprinkling unless you really enjoy periodically cleaning horrid gunk out of filters. Also, unless you're really careful about your choice of detergent, you can easily poison plants and destroy topsoil with laundry wash water. Bathwater is generally OK.

Running a flood of grey water over a lawn surface will make it unpleasantly soggy near the outlet pipe and, depending what's in the grey water, might make the lawn nasty to be near. If you're going to use grey water for a small lawn, do it the way I outlined above: plant your grass in sandy, porous topsoil, fed from a mulch-filled distribution trench, over a carefully graded compacted clay base. Don't bother using grey water on a large lawn.

The best grey water advice I've seen is from Art Ludwig at Oasis Design, and he doesn't like using it on lawns.
posted by flabdablet at 6:58 AM on March 16, 2007

Thanks everyone - my fears are confirmed. I think I will go with pop-ups attached to an automatic timer.

As it happens, I will be sowing with weeping grass, a drought tolerant local native.
posted by wilful at 3:28 PM on March 16, 2007