This is the easy way to figure out how much water your drip irrigation system is putting onto the garden.
Take your entire length of drip hose (one of the units) say it’s 50 feet long. Put it all in a 5-gallon bucket. Turn on the hose and see how long it takes to fill up the bucket. That length of time is the amount of time it takes to apply 5 gallons to the garden – let’s say it takes 20 minutes to do this.
If you want to eliminate this step, I’d go with the industry norm of 1 gallon of water per foot of hose per hour. So a 50-foot commercial drip hose will put out 50 gallons of water an hour.
The simplest thing to do is to run the drip hose for an hour. Go out with a shovel. Drive the shovel down about halfway to the edge of the wet area and pry the blade sideways so you can see a cross-section of the soil. You’ll see how far down the water has penetrated.
In practical terms as long as it’s really wet at least an inch down, you’re going to be fine.
But repeat the shovel test two days later. If it’s dry, you know you have to leave the hose on for longer. If it’s still really wet, then you get to use less water.
But here’s the critical thing. The plants you have growing there (are they water hogs?) or do you have clay soil or ?? Any number of individual variables are going to come into play when you decide on your watering schedule.
This is why it’s critical to do that shovel test to physically see the impact of your watering.
Test! Don’t guess.
But If You Want To Go All Technical… 🙂
Your drip system is going to apply water between 2 and 3 feet wide (depending on your hose and the soil. Lay a hose on the ground and let it run for an hour. See how far the water spreads. Let’s say it spreads 3-feet.
And that it’s 50 feet long (as above). That means the hose has a coverage area of 3×50 = 150 square feet. If we put one-inch water onto the garden, we now have to do the following math.
150 square feet = 144×150 (144=number of square inches in a square foot) =21,600 square inches.
Apply one inch of water and we have 21,600 cubic inches. Divide by 231 (231 cubic inches to a U.S. gallon) and we have 93 U.S. gallons of water. (5 U.S. gallons = 4 Imperial gallons)
If it took 20 minutes to produce 5 gallons, it’s going to take 93/5 =18 times 20 minutes or 360 minutes. So 6 hours of watering will put on 1-inch of water.
Again, if your drip system is faster or slower or your soil allows water distribution in a different width, your numbers are going to be different.
Drip will always be slower and take longer than you think. 🙂
But that’s how you figure it out.