DIY Gravity Drip Irrigation

I do it by starting with a stack of free pallets saved from an undignified demise in a landfill. There, the wood would turn into gases that amplify climate disruption. By using sturdy, free pallets as a base on which to raise a rain barrel up a few feet, you, too, can “fool” water into pushing uphill to feed soaker hoses in your garden beds. Here’s how.

How Much Pressure for Gravity-Fed Drip Irrigation?

• 1 gallon of water = 8 pounds
• 1 cubic foot = 7.5 gallons of water = 60 pounds
• 300-gallon container x 8 pounds = 2,400 pounds
• A vegetable garden in summer needs roughly 1-gallon of water per square foot per week.

Tools & Materials for IBC Rain Barrel

• Stake
• Twine
• Line level
• 4-foot level
• Pallets
• Blocks of 6×6 pressure-treated wood, cinder blocks, or bricks
• Chicken wire
• Rubber pond liner, metal roofing, or rolled roofing
• IBC tote
• Exterior-grade paint for plastic
• Brass spigot
• Spade bit that matches the inside diameter of threads of brass spigot
• Exterior-grade caulk
• Downspout diverter with watertight connections

Choose a Proper Rain Barrel

Vegetable beds in summer need roughly 1 gallon of water per square foot per week. For example, a 4-by-12-foot bed equals 48 square feet, and in dry conditions, it needs about 48 gallons of water each week. That means a 50-gallon barrel can water one bed for an entire week, or until the next rain refills it. You could set up a whole series of barrels, but that would multiply the cost of connections and the time to install them.

I recommend International Beverage Containers (IBCs) that have held non-toxic liquids. I call them “super rain barrels.” You can find IBCs advertised on Craigslist for about $75 to $150 apiece. They’re worth it. I figure, if it holds more gallons than it costs in dollars, you’re getting a good deal. And IBCs hold about 300 gallons — six barrels’ worth, but with a smaller footprint and less connection hardware required. IBCs are nearly a cube (48 by 48 by 40 inches) of food-grade plastic stiffened by an aluminum cage screwed to a pallet. On top is an 8-inch-wide screw-on lid. At the bottom is a 2-inch plastic spigot. The ones I’ve bought still had the faint scent of the almond oil they originally contained. The plastic is translucent, so to keep algae from growing inside, I slap on a couple of coats of dark-brown paint that’s made for plastic.

Connect to the Downspout

I recommend using the metal downspout diverter sold in the Gardener’s Supply catalog. It’s a box with a hose and connectors, and it inserts into the downspout after you’ve cut it open with snips or a metal-cutting blade. It feeds water into a horizontal length of hose that connects to your rain barrel. Install it correctly (meaning, follow the directions), and you won’t need to install an overflow hose. That’s a big timesaver. When the rain barrel is full (and all valves and the lid are closed), the rainwater will back up in the hose and goes down the original downspout.

Installing it correctly means the inlet to the rain barrel is at the same height as the diverter. If you want to set up your rain barrel farther from the downspout than the short Gardener’s Supply hose will allow, you can buy a 3⁄4-inch plastic hose used in standard drip irrigation systems. These are often sold at big box stores (or some might be lying around in your shed). Just be sure not to use a clear plastic hose. Algae will grow inside and clog it up.

Build a Super Base for Your DIY Rain Barrel

Even if your garden is downhill, an IBC rain barrel will work best if it’s stacked on enough pallets that you can set a bucket or watering can under the barrel’s plastic spigot. You can get free pallets from feed and seed stores, garden centers, HVAC contractors, or big box stores. If the pallets have “HT” stamped on the side, they’ve been heat-treated and don’t have chemicals in them. Most pallets that have been treated with chemicals have bright paint on the side and are expensive, so stores send those back for credit. IBC containers already come with one pallet screwed to the cage. Unless that pallet is plastic or metal (and therefore water-resistant), remove it from the bottom of the IBC and add it to your pallet stack.

I’ve seen some people with modest carpentry skills build flimsy bases from scraps of wood. They must not realize that a 300-gallon tank of water is heavier than a ton. That’s why I think a stack of pallets makes the best base. Not only are pallets ready-made and free, but they’re also quick to assemble, built to support a lot of weight, and won’t fall apart.

We’ll determine how many pallets you’ll need to use to send water uphill in the next section. First, I want to familiarize you with the steps for making a sound base for your rain barrel, regardless of its height.

Once you have all the pallets you need, raise the first one off the ground by putting one cinder block fully under each corner. Bricks or scraps of pressure-treated lumber will work fine as a foundation too. The main thing is to get the pallet wood on a rot-proof foundation at least 5 inches above the ground so it won’t decompose. If you’re building on clay soil that shifts over time, use a couple of 4-foot lengths of pressure-treated 6x6s to distribute the weight more evenly. Level up the foundation, and then start stacking pallets. Weight and friction will keep the pallets from moving around; no need to screw them together.

Then, wrap the pallets and foundation with some chicken wire to keep critters from making a home inside. Extend the fencing as an apron on the ground around the foundation to keep critters from digging their way under the pallets.

Finally, use something waterproof and UV-proof to keep the pallets dry: try scraps of pond liner, rolled roofing, or scraps of metal roofing. Most tarps won’t stand up to UV radiation, so don’t use them.

I used a few pieces of pressure-treated lattice to cover the sides of my pallet stack to make it look a little more like a garden feature, but that’s not necessary.

Once your pallet stack has a foundation, critter-proofing, and a roof, the empty rain barrel can be put on top. It should be light enough for one or two people to lift it into place. Short of a tornado, its weight will hold it down. If you do have tornadoes, don’t screw the aluminum cage down through the foundation’s roof material; you don’t want to let water rot out the pallets. Instead, screw a couple of pressure-treated 2x2s, vertically and on opposite sides, into the top of the IBC’s aluminum cage and the bottom of the pallet stack.

Let Water Flow

Some people remove the 2-inch plastic spigot and use lots of PVC adapters to dial down the diameter so a brass spigot can replace it. I tried that once and found that the adapters seriously constricted the rate of flow. Not only that, but I missed having a big spigot that could fill a 5-gallon bucket or a 2-gallon watering can in a matter of seconds. So now, I keep the 2-inch plastic spigot in place and make a dry, level area underneath it with bricks, where I can set a bucket or watering can and fill them quickly.

To attach a garden hose, I affix a brass spigot about 4 inches above the bottom of the barrel. To do this, I use a spade bit that cuts the same diameter as the inside diameter of the threads of the spigot. That way, the outer edge of the threads will bite into the plastic as I screw it into place. Just before it’s screwed all the way in, apply a bead of exterior-grade caulk around the threads, and then screw it into the last bit. Leave the caulk to cure for 24 hours before moving or filling the barrel.

Send Water Uphill

Here’s the fun part. I had a good site for my rain barrel, but my garden was up a gentle slope. Carrying water by hand was out. Installing a pump and routing was too expensive. Besides, pumps like to break down. But I knew the water would run uphill through a hose if the inlet was higher than the outlet. This is the same principle that lets a city water tower supply your house. If I stacked the pallets just a tiny bit higher than the high point of the garden, gravity would push the water uphill into the beds. Follow these steps before building your pallet stack, and you can do the same:

1. Drive a stake into the high point of the garden, and wrap twine around its base at ground level.
2. Pull the twine to where the rain barrel will be stationed.
3. Hang a pen-sized line level on the piece of twine.
4. With the twine pulled tight, adjust it until it reads level.
5. Measure the distance of the twine that’s above ground level. In my case, this was about 35 inches.
6. If the brass spigot of your rain barrel is a couple of inches above that height, the water in the hose will “think” it’s going downhill, even if the hose lying on the ground is actually running uphill.

Pallets are about 5 inches tall, and I had some 6×6 scraps for a foundation. In this case, six pallets plus the foundation put the brass spigot of the barrel just above the high point of the garden. Gravity would send the rainwater flowing uphill. I laid a garden hose from the barrel to the high point. From there, a soaker hose would carry water back downhill (a soaker hose running uphill loses most of its water right away). Whenever I wanted to water the garden, I turned on the brass spigot. Water flowed uphill through the garden hose, then flowed downhill through the soaker hose to be evenly distributed across that row.

Rain Barrel Maintenance

Your rain barrel should be mostly maintenance-free. Close the spigots when the barrel is empty so it will refill during rains. Come winter, leave the big spigot open so water doesn’t freeze inside. Depending on conditions, you may have to touch up the paint periodically to keep algae from growing. Keep an eye out for critters setting up residence in the pallet stack if your fencing isn’t tight enough. Keep your rain gutters free of leaves in fall and oak flowers in spring (hopefully you’re doing that already). And then, enjoy tons of free water from your super rain barrel.

Frank Hyman, a former organic farmer, is the author of the DIY chicken-keeping book Hentopia, as well as The Absolute Beginner’s Guide to Foraging Mushrooms Without Dying.