How Much is an Inch of Water?

How often and how much should I water my flower beds and vegetable garden? Same question for my newly planted trees. The care instructions that arrived with my plants say “an inch of water” either weekly or twice weekly.

In the past, my watering habits tended toward neglect. I’d water after a couple of weeks without rain or when plants looked wilted enough to be dying. I don’t recall my mother or grandmother watering their gardens and I can almost guarantee that my gardening neighbors don’t water. At least I’ve never caught them at it!

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But okay, I’m into following written rules. After a string of sunny days sans rain, I got out my hoses and started watering. Then I realized – uh oh! How much is an inch of water?

I took off to Google, hoping to find something like the guidelines for washing your hands: sing Happy Birthday before the final rinse. Maybe I could sing one of my old Girl Scout songs. Wouldn’t that be easy?

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But the answers I found were not that easy. The first and most frequent guideline was the old tuna can. For example: “My dad said to put a tuna can next to my roses and water till the can is full which would be about an inch.” Okay, great. I don’t have roses. Does that apply to all flowers? And what size tuna can are we talking about?

A lot of the tuna-can answers noted that “grandpa said…” And did that mean someone the age that MY grandpa would be if he was still alive? Maybe back then tuna came in only one size, leaving me with the question, what size tuna can? And what happens when I’m watering a new tree? The tuna can is going to get full awfully fast.

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Some answers involved what I consider higher mathematics. For example: “An inch of rain is exactly that, water that is one inch deep. One inch of rainfall equals 4.7 gallons of water per square yard or 22,650 gallons of water per acre.” Now what am I supposed to make of that?

Another website suggested “To determine if the soil has been watered enough, dig into the soil beside the hose. If the water has seeped 12 inches down, it’s about time to turn the hose off. Remember how long this took for the next time around.” Really? So I need a hose, a shovel, a ruler, and a stopwatch. Oh good grief!

One of my favorite higher mathematics suggestions asked me to find the gallons per minute (GPM) flow rate of the sprinkler being used from the package of the manufacturer. Even assuming I still had that information (I don’t) and assuming I’m always using a sprinkler (I’m not), I still have to do things like multiply the square footage to be watered by .62 gallons or 1 inch of water per square foot. Okay, now my head hurts.

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Still another website suggested that I set out a rain gauge. Well, been there, done that, and what does a rain gauge have to do with knowing how much time it takes to water? After all, sometimes it rains an inch an hour and sometimes an inch a day.

Even if I take any of these steps, I need also to account for the variables such as root depth of the particular plant being watered and average temperature.

Finally, several sites suggested I buy a flow timer. Since I’m already drowning in gardening equipment (no pun intended), I think I’ll pass.

None of this has solved my problem – how long do I water for an inch of water?

I’ve decided to disregard the expert advice, especially since the guidelines make little sense to me. Sure, if I’m using a sprinkler I could probably measure with a tuna can, a glass, or a bucket, and then time how long it takes to get to an inch. But I’m not.

So what will I do instead?

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Unless it rains, I will water twice a week. You’ll find me hauling hose on Wednesdays and Saturdays. I plan to water until I think I’m done. I suppose time will tell if I’ve watered enough.

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11 thoughts on “How Much is an Inch of Water?

  1. You found the right answer after all: let your plants tell you when they need water and how much. Gardening is no fun if you have to use math.

  2. I was told by someone I trust to “count” as I water each plant. She counts to 60, using the 1-mississippi method. I am too impatient for that, but I do count now, getting a good rhythm going and making sure I am fair to all the plants. We put in soaker hoses in an effort to get it right, , and I left them on for almost 10 hours once, nearly wiping out a garden bed… >sigh< nothing like learning the hard way. Twice weekly sounds like a plan!

    • Hi Jo! That’s the first helpful thing I’ve heard. Counting to 60 using 1-Mississippi-2-Mississippi would mean a full minute. I’ll bet I can find a song that lasts a minute… Thanks!!

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