Large trees need lot of water, and flooding is a great way to supply it

Sunset  – September 3, 2004

Flooding (soaking) is an effective way to supply sufficient water to the extensive, deep root systems of large shrubs and trees. Make a level basin for the plant by forming a ridge of soil several inches high around its drip line. You’ll usually need to fill the basin more than once to ensure that water penetrates throughout the entire root zone. If the soil in the basin hasn’t absorbed all the water within a few hours, make a channel in the ridge around it to let the excess drain away.

If you grow vegetables or flowers in rows, you can build adjoining basins for large plants like squash or make furrows between rows (see illustrations right). To minimize damage to roots, it’s best to construct the furrows when the plants are young, before their root systems have spread. Broad, shallow furrows are generally better than deep, narrow ones: the wider the furrow, the wider the root area you can soak, since water moves primarily downward rather than laterally. And a shallow furrow is safer for plants–nearby roots are less likely to be disturbed when you scoop out the furrow, and they’re likewise less apt to be exposed by a strong flow of water through it.

Watering in Furrows and Basins

Furrows 3 to 6 inches deep help irrigate straight rows on level ground. Bubbler on hose end softens flow of water to prevent erosion. This method is good for crops that don’t appreciate overhead watering. It works poorly in very sandy soils, however.

Basins with sides 3 inches high hold water around large plants, such as tomatoes and peppers. On level ground, link basins to make watering easier.