What people use it for
- The twenty minute myth Where that number came from, and why your sprinkler is putting down a third of what the article assumed.
- Water that soaks in Clay gets the run split in two, sand gets a third day. Same water, different delivery.
- Seed and sod Two schedules that do not look like lawn watering at all, and the tool has both.
Why the minutes in the articles do not work
Most advice on this comes back to one line: an inch of water a week, twenty minutes three times a week. The second half of that sentence is what burns lawns, because twenty minutes is half an inch on a pop-up spray zone and a fifth of an inch on a hose-end sprinkler. The inch is the measurement. The minutes are only a translation of it, and the translation depends on the sprinkler in your hand.
So this tool starts from the inch and works backwards through your grass, your sun, the week you are in and the rate of your own sprinkler. Two lawns on the same street can need 25 minutes and 75 minutes per zone, and neither of them is wrong.
The can test, in fifteen minutes
Put five or six straight-sided cans around one zone, run it for fifteen minutes, and measure the depth in each with a ruler. Multiply by four and you have the rate in inches per hour. A can holding a quarter inch means one inch per hour, and a can holding an eighth means half an inch per hour.
Do it twice, on a calm morning. The cans at the edge of the pattern usually come up short, which is the useful part: the same fifteen minutes puts down twice as much in the middle as it does at the end of the throw. If the edges are dry and the middle is soaked, the fix is to run the zone twice for half as long, not to run the whole thing longer.
What the week is made of
Cool-season grass (fescue, bluegrass, ryegrass) wants an inch to an inch and a quarter a week in summer. Warm-season grass (Bermuda, zoysia, St Augustine) does well on less, around three quarters of an inch. Full sun takes the top of that range, shade takes the bottom, and a week over ninety takes more than a mild one.
The tool puts that water into two runs, or three on sand, because one long run on a sandy lawn is water that keeps going down past the roots. Clay gets the opposite treatment: the same water in two shorter passes half an hour apart, so it soaks in instead of running off the surface.
| Sprinkler | Inches per hour | Minutes for half an inch |
|---|---|---|
| Hose-end oscillating | 0.2 to 0.3 | 100 to 150 |
| Impact sprinkler | 0.3 to 0.5 | 60 to 100 |
| Gear-drive rotor | 0.4 to 0.6 | 50 to 75 |
| Pop-up spray head | 1.0 to 1.5 | 20 to 30 |
New seed and new sod are not lawns yet
Seed needs the top inch wet, not the root zone. Three short cycles a day, every day, until it comes up, then two, then the lawn schedule once it has been mowed twice. A single long soak on bare seed washes the seed downhill and leaves the surface dry by noon.
Sod is the other extreme. It is living grass with cut roots, so it wants a wet day, every day, for two weeks, and after that it wants to be treated like the lawn it now is. Pick either one in the tool and the schedule changes with it.
When in the day
Early morning, before ten. Water at noon and a good part of it evaporates before it lands. Water at night and the blades stay wet for twelve hours, which is how fungus gets started. Wind is the other thing to dodge: it takes the pattern sideways and leaves stripes that dry out first.