How to Keep Thirsty Lawns Happy
I have often written that our lawns need about an inch of water a week to stay green in our (usually) dry summers. The standard advice is to place empty tuna cans around the lawn, then run the sprinkler or irrigation system to see how long it takes to fill the cans with an inch.
When you know how long it takes to reach the desired line on the can (about half an hour for me), you can water accordingly. You also will discover where your watering system doesn’t reach and where it reaches a little too well.
A very clever reader reports that “the tuna can thing” doesn’t work for her but is easily replaced by a little math. To learn how much it would cost to keep her lawn green, she determined the square footage of her lawn and the cost of water.
If you are up for it, here’s what she did:
- Her lawn being a semicircle, she did the math: Pi times the radius squared gave her a total of 981 square feet. (I wish you could see the neat diagrams and mathematical notations she included. I am very impressed.)
- She then figured out the volume of water needed for an inch a week by deciding that volume = area x height (at which point I lost my grip). OK: 981 square feet x 1/12 foot = 82 cubic feet of water per week, which at 7.5 gallons per cubic feet comes to 613 gallons.
Yipes! My reader’s usual water consumption rate is $1.50 per 100 cubic feet, so she figured it out: $1.50/100 cubic feet x 82 cubic feet = $1.23 per week, or about $11 per two-month billing cycle. The base rate, she notes, goes up if she exceeds 5,000 cubic feet per billing cycle. To determine when she has used her 82 cubic feet of water, she watches her meter. When no other water-using appliance is running, she records the meter, which read 667.46 on the day in question. She added 0.82 for the 82 cubic feet, then noted how long it took to reach the target number of 668.28. At that point, she knew how long to run the sprinkler to give the lawn an inch of water.
I was exhausted just thinking about it. Whew!
Well, I don’t know about you, but I still like the tuna can thing. Cat food cans work fine too. Set them around the yard, as I said, and see how long it takes to fill them up.
Now here’s a lovely trick: Once you know how long you need to water, you can set a hose timer to shut off the water for you. You can even set it to run once or twice a week for however long it needs to and turn itself off. My Gardena hose timer cost about $25 and has lasted for about 10 years so far.
There are, of course, other options, such as not watering the lawn. When I first moved to the maritime Northwest, I was amazed. Everywhere else I had lived, the grass was naturally green in summer and brown in winter. Here, it was naturally green for about nine months of the year and brownish for maybe three months.
At first, I worried that the lawn was dead. As soon as the autumn rains returned, so did the lawn. I quickly realized that mature turf grasses adapt to summer drought by going dormant.
This, however, is only true for established lawns with strong, deep root systems. Brand new baby lawns, and most sod lawns, will not just go dormant. They will go to grass heaven and probably not come back.
To get a lawn to the point of sturdy independence takes around two to three years. Start by raking in half an inch of compost every spring and fall. Follow up by not feeding with high nitrogen, but instead, spreading corn gluten in fall. The usual rate is 20 pounds per 1,000 square feet. (You don’t need a tuna can for this equation; just do a rough calculation of the overall area of lawn and be generous.)