Two watering days a week and what it does to a lawn

Folsom assigns landscape irrigation days by street address, and the days depend on the water conservation stage the city is in. Under the Stage 2 rules the city has published, odd-numbered addresses irrigate Tuesday and Saturday, even addresses Wednesday and Sunday, and nobody irrigates Monday, Thursday, or Friday. The stage moves with conditions, so the city water conservation page is where to check what applies right now.

The near-universal first reaction to a two-day schedule is to double the run times. It is also the one adjustment that reliably makes the lawn worse.

Why longer runs do not work

Soil accepts water at a fixed rate, and that rate falls as the soil wets up. Sprinklers apply water at a fixed rate too. Once application exceeds infiltration, everything after that point runs off. On the tighter soils common around Folsom the crossover often arrives four to six minutes into a cycle, which means a twenty minute run spends three quarters of its life sending water down the gutter while the root zone stays dry.

What does work

Split the total time into short cycles with gaps between them. Three seven minute cycles an hour apart deliver far more usable water than one twenty minute run, because each pass stays under the intake rate and the gap lets the previous pass move down.

To find your own numbers: run one station and stand outside with a timer. Note the minute water starts leaving the area. Set the cycle a minute shorter than that, then repeat it two or three times with at least a 45 minute soak between. Most controllers made in the last decade have a cycle-and-soak setting; older ones do the same job with multiple start times.

Two more adjustments matter as much:

• Water early. Finishing before sunrise avoids the worst evaporation losses and does not leave foliage wet overnight.
• Use seasonal adjust. The controller should not run the same programme in April as in July. Four adjustments a year cuts annual use more than any equipment change.

When to stop trying

A lawn under a two-day schedule can be kept green if the programming is right, the soil is prepared, and the coverage is even. The honest question is whether it is worth it.

A lawn that children or dogs use every week earns its water. A lawn nobody walks on, kept alive because it came with the house, is the most expensive surface on the property and it delivers nothing that a well-designed low-water planting would not deliver better. Conversion runs $8 to $18 per square foot installed, and the lawn replacement guide covers what that buys.

Keep the part of the lawn that gets used. Convert the part that does not. That is usually the front, and it is usually the bigger half.