Subsurface Drip

Most watering wets the ground surface and loses part of it to evaporation off damp soil and leaves and to wind carrying the spray sideways. Subsurface drip buries the line: a tape or tube laid roughly 25 to 35 cm (10 to 14 in) down, with small openings spaced along it - emitters - that let water seep straight into the root zone. Nothing is applied where roots cannot reach it, so little is wasted and less fertiliser is washed past the roots. The surface stays dry, which is a consequence rather than a bonus: fewer weeds come up between the plants, and fewer seedlings do too.

Clean water at a steady pressure is a precondition rather than an improvement. The supply is filtered first - screen openings about a tenth of the narrowest passage inside an emitter - and slightly acid water is preferred, because a high pH drops dissolved minerals out as scale. The soil has to draw water upward: on very sandy ground it will not rise far enough to wet the surface at all, so seed and transplants need a separate surface method until established. Ground wants to be level or smoothly graded, since water spreads only a short way sideways from the line.

It is buried, so it fails silently: a flow meter and a pressure gauge are the only way to see it. Pressure falling while flow rises is a leak; high pressure with low flow means blocked emitters or a crushed line; a slow decline means emitters plugging one by one. Blockage has three causes and three cures - mineral scale needs acid, slime from algae and bacteria needs chlorine, sediment needs filtering and flushing - and roots pinching the openings and rodents chewing the tube account for most of the rest. Weekly flushing at first, and chlorine held at 1 to 3 parts per million for half an hour to an hour, are what separate the 15-year design life from systems still running after 25 seasons; neglect cost a third to a half of surveyed systems their evenness.