How much should you cut back your sprinklers in October in Suisun City?

In October, cut your sprinklers back to about half of their July run time. The University of California's Lawn Watering Guide for California (ANR Publication 8044) lists how many minutes a week a lawn needs in each month, and in its inland valley tables October comes in at roughly half of July. By November it's about a fifth. A timer that still runs its summer schedule is putting down close to twice what the lawn can use.

That gap is easy to miss. The lawn still looks fine in early October, and nothing on the controller tells you it's still running July's times.

How much less water does a lawn need in October than in July?

UC's guide gives the numbers as minutes per week for each month, by region and by how fast your sprinklers put water down. Its map draws region lines right through this part of the state, so we compared the two inland tables nearest Solano County, Northern Inland Valleys and Sacramento Valley. They agree to within a few points. For a cool-season lawn like tall fescue, here is each month as a share of July:

• September: about 70 percent of July.
• October: 43 to 50 percent of July.
• November: about a fifth of July.
• December: about a tenth of July.

Warm-season lawns such as bermudagrass follow the same curve in the same tables, with lower minutes all year. The guide says plainly that weather varies from year to year, and that "ideally, you should plan to re-set your automatic irrigation system monthly during the growing seasons." That means a September change, an October change and a November change, not one big switch.

Should I cut the minutes or the watering days?

Both, and Suisun City leaves that choice to you. The city's water use rules let customers water "any day of the week and as frequently as necessary, so long as the use is not wasteful," so there are no assigned days to work around.

UC Healthy Lawns suggests about three waterings a week for cool-season grass and adds that "fewer applications may be sufficient during cooler months." A sensible October move for most lawns is to drop one watering day and shorten the rest. UC's lawn watering card gives the test for whether you went too far: most lawns need water when the top 2 inches of soil have dried out. Dig a small plug with a trowel in the driest corner a day before the next scheduled run and feel it.

If you see water running off after the cut, the run is still too long for the soil to take in one go. UC's advice is shorter watering times more often, so the water moves in instead of across.

How do I use seasonal adjust on my sprinkler controller?

Seasonal adjust scales every run time by one percentage, so you don't have to reprogram each zone. Rain Bird's support page says 100 percent "is representative of irrigation during the average hottest time of year." If your schedule was set for July, an October setting near 50 percent lines up with UC's numbers.

Two things catch people out. A manual setting stays where you put it until you move it, so a 50 percent October setting is still 50 percent next July unless someone turns it back up. And a controller without the feature needs every zone changed by hand, every month this fall. Rain Bird's ESP-TM2 and ESP-ME3 controllers support manual seasonal adjust, and its app can send an automatic value each night based on your postal code's usual weather and the forecast.

If your timer is old, confusing or keeps losing its program, that is usually a sprinkler controller replacement job rather than something to fight with every season. Setting the schedule is part of it. One of our Google reviewers, Zac, wrote that the crew "even programmed a weekly schedule for our lawn to be watered."

How do I know how much water my sprinklers put down?

Run a can test. UC's guide asks for six or more straight-sided containers of the same kind (empty tuna cans work), spread evenly on the lawn. Run the zone for 20 minutes, measure the water in each can with a ruler, average them and multiply by three. That's how many inches an hour the zone puts down, and it tells you which column of UC's table to read.

The test also shows coverage. If one can is nearly empty while the others fill, more minutes won't fix that brown patch. UC's guide says to look for broken, clogged or malfunctioning heads first, and to repeat the test after any repair. A sprinkler system diagnostic tests the controller, wire, valves, pipe and heads in order, runs every zone and puts the findings in writing.

When should I turn the sprinklers off for the rainy season?

When the rain does the work. UC's watering card puts it simply: "Shut off your irrigation system during rainy weather." Suisun City's rules go further and bar outdoor watering within 48 hours of measurable rainfall, which the city defines as rain that makes puddles or runoff, or more than a trace measured at Travis Air Force Base.

Our rain mostly falls from November to March, so October is usually still a watering month, just a lighter one. By December UC's numbers are down to about a tenth of July: 8 to 13 minutes a week for a cool-season lawn at a typical output of 1 inch an hour. UC's guide also says to be sure to restart the system once a rainy spell has passed.

A rain sensor or a weather-based controller handles that on and off for you. The Solano County Water Agency pays half the cost of a WaterSense-labelled weather-based controller, up to $300 for a home, and asks you to read its terms before you buy. Our lawn and irrigation rebate finder shows which programs your water provider runs, and watering rules by city covers the hour limits in neighboring towns.

What to do this week

Find the run times your controller used in July and write them down. Set seasonal adjust to about 50 percent, or cut each zone by about half if it has no such setting. Then run a can test on the lawn zone that always browns first, and check the top 2 inches of soil before the next run.

October is also the month we schedule aeration and overseeding for cool-season lawns, once the heat has broken. If you'd rather hand off the schedule along with the lawn, our Suisun City lawn, sprinkler and lighting page shows what that covers.