We love our arid climate, but realize that it can make gardening a challenge. On average, we get less than fifteen inches of rain per year, which is almost 1/3 of what I am used to growing up in Pennsylvania. In an attempt to provide more consistent and conservation-minded water to our garden we’re installing a drip irrigation system utilizing 5/8″ drip tape gravity fed from 55 gallon plastic barrels.
In the above picture, you’ll first see that I have elevated the barrel on a few cinder blocks in order to create slightly more water pressure from gravity. The barrel was originally a white color and I painted it black so that a.) sunlight penetration is reduced which will prevent algae growth and b.) the water will heat up in the barrels. Using warmer water will reduce shock that the plants might have if the water was colder. A threaded PVC nipple was JB Welded to the side of the barrel one inch up from the bottom. It is one inch above the bottom because I don’t want to draw any sedimentation into the lines that may collect at the bottom. Between that and the hose I have a brass shutoff coupling. The supply line running between the beds is the cheapest garden hose I could find. I cut pieces to fit each row of beds.
Each bed has two driplines running down the length of the bed. Beds, by the way are 30″ wide and 20 feet long. Everything is uniform, which will allow interchangeability. We plan on getting several years usage out of the tapes and this way we can easily install them next year, not needing to worry about where each tape goes. Each tape line begins at the supply line, coming through another shutoff valve. That shutoff valve has a barb on one side that you push into the hose (I used a cordless drill to make the appropriate size holes in the supply hose first) and the other side connects via a coupler to the 5/8″ drip tape. The tape and the shutoff valves are from Farmtek. At the other end of the tape, fold it over on itself twice to crimp closed and then fold lengthwise. Then slide a 1″ section of drip tape over the fold to hold it together.
Having every line on a valve gives you maximum control of water. Some beds contain a crop that is harvested early in the season, and once done you could turn that bed off to save water.
To calculate how much water you’ll need, we estimate that each bed will need 1″ of water per week. A bed if fifty square feet. That translates to ( 50 / 12 x 7.48 ) 31.16 gallons per bed per week. Said differently, I’m dividing fifty by twelve to find the cubic feet of water that 1 inch of rain on that bed would represent. One inch of rain would be 1/12th of a cubic foot of rain. One cubic foot of rain water on a 50 sq ft bed is 50 cubic feet and that would be twelve inches of rain. Then convert to gallons by multiplying by 7.48. Most of our lines are set up to water seven beds at once and I assume (perhaps incorrectly) that each bed is getting an even amount of water. So, you could fill your barrel to the 30 gallon mark every day of the week and know that all seven beds are getting 1″ of water over the course of seven days.