SFG Drip Irrigation

A few days ago, we wrote about how we set up our square foot gardens on our front and back decks, and noted that the soil dried out quickly because it was only six inches deep.  About halfway through the summer we got smart and set up a drip irrigation system to help keep the soil moisture consistent, save water, and compensate for our absentmindedness in watering.  We ended up with two similar but distinct systems for the front and back deck, but they both work well enough to blog about!

On our front deck, we've got two five-gallon buckets that we use as simple reservoirs in a gravity-fed system.  We started by drilling holes in the buckets that are about the same size as our fittings (see next picture).

The fittings have pipe threads on one side and a hose barb on the other.  The exact size isn't too important, but the holes, barbs, and tubing have to be consistent.  We've got 3/8" holes and 5/16" tubing (if we're remembering correctly).  If the threads on the fitting are NPT, they'll be slightly tapered.  It's good to make the hole roughly the same size as the small end so there's a better chance it won't leak.  Wrapping the threads with Teflon tape can also help.

It still leaked a little, even after adding the Teflon tape, so we made a washer out of a piece of rubber.  This one is a piece of rubber pond liner, but it could also be a piece of spent bike inner tube or even something from the hardware store that's actually meant for this purpose.

We made ours two layers thick and stuck it on the tube fitting like so.

Last year it didn't leak, but this year it makes a slow drip...almost exactly at the rate we want for our watering.  So, not being perfectionists, we'll just position the fitting over the edge of the garden!

Cinder blocks make a nice stable base for the reservoirs.  Once we had them and the buckets in position, we cut the tubing to the right length (about four feet, so it reaches across the square foot garden).  The closest one in the picture is buried under the dirt for a stretch.

At the end of the tube, we folded it over and pinched it shut with a clamp.  There are probably more elegant ways to do it, but this works.

Now it's time to punch holes in the tubing so it drips out at the right rate (probably about 1 drip per 3 seconds).  There's definitely an art to this part.  We found that a needle is too small, but a 1/8" drill bit is too large.  The way that worked the best for us was to cut a small slit with a knife.  It's easier to see the drip rate if the buckets are filled with water first.

Lookin' good!

Oops!  We made this one too big.  Be careful not to do this.  Also be careful not to cut yourself, or you'll have to make the rest of the holes while clenching a piece of toilet paper in your other hand.

We were able to mostly salvage the too-large hole with a clamp.  This technique doesn't work quite as well if you cut yourself.  It turns out that if the drip rate is just right when you the holes are first cut, it will slow down and eventually stop a few weeks afterward. Probably a biofilm of bacteria is building up in the slit and eventually becomes thick enough to stop the flow (although we haven't scientifically verified that).  What works best for us is to start out with the drip rate a little bit too high, which still slows down over time but takes longer to stop completely.  Then every couple weeks we bend the hose near the holes to get the water dripping again.  Other than that, the only maintenance is to fill the buckets with water when they get low.

On the back deck, we've got a 20-gallon fish tank as the reservoir.  It's positioned under the roof line so it fills automatically whenever it rains. (1/4" of rain will fill it completely.  It's amazing.)  Also, the bottom is at a higher elevation than the garden.

For this one, we just use a siphon system.  We added a fitting to the end of the tubing just to keep it near the bottom of the tank, then ran the tubing out over the top and down into the garden.  We took a quick sip on the far end of the tube to get the siphon flowing, then when the tube was full of water, folded and capped with a clamp as above.  We only had to suck on the tubing until the water got about halfway to the end.  That way we didn't get any rainwater in our mouths.

We routed the tube around the plants (we even added a lemon tree in between just for fun) and cut holes in the tubing as above.  Since rain fills the reservoir, this system is even lower maintenance than the first one!  We do still have to bend the tubing to free up the holes every few weeks, but overall it works pretty well.  We've normally got two or three tubes running from this one, but the only thing in the garden so far is a few broccoli plants so we just left it at one tube for now.

We like the siphon system better than the bucket system.  It's easier to set up, requires fewer parts, and doesn't have any leak concerns (unless we cut the holes in the tubing too large).  Come to think of it, we could probably make a siphon work with the buckets, too.  We'll have to keep that in mind for next time.

Have you set up a drip irrigation system for your own garden?  How have you maintained a proper drip rate?  Tell us about it in the comments section below!