Saturday, January 12, 2019

Keeping my herbs alive: An indoor watering system

IMG 2815As I was again reminded in a recent Twitter thread, I like having fresh herbs. But you often don’t need a lot of them, which in turn means that it’s nice to have some pots of them growing at home so you can snip off just a little bit rather than buying 20 times what you need at the store. 

The problem is that 1.) I travel and 2.) I forget to water plants. One common low-tech method for automatically watering is to fill a wine bottle (or soda bottle, etc.) upside down in the soil. This works reasonably for a few days but my issue was the 2-week plant-killing excursions. So I looked around for commercially-available solutions.

There were a few systems online but at least one of them had to sit up above the plants, which wasn’t really feasible for my setup. And none of them seemed to have very good reviews. So I decided to see what I could come up with myself. I already had a small hydroponics system in the same room which turned my thoughts to supplying the water from an aquarium pump in a bucket of water on the ground hooked up to a timer. This is indeed what I ended up doing but getting to a system that actually worked took a fair bit of fiddling and experimentation.

My first thought was to “borrow” the aquarium pump I already had to keep my hydroponics system topped off in the summer and use some T-connectors to fan out the tubing so that I could water multiple plants. To make a long story short, the pump I had wasn’t powerful enough to lift water and force it through a network of T-connectors. Elevating the bucket on a stool helped. Sort of. But if I lifted it too high, the water started siphoning when the pump turned off. Furthermore, as I discovered when I experimented with different tubing sizes, in a network of tubing like this, it’s hard to get relatively even flows out of the different lines.

What ended up working the best had three basic elements:

A more powerful aquarium pump (head of about 8 feet)

A manifold intended to split the output of an aquarium air pump

A digital timer with 1 second resolution

The manifold was really the key thing here because it splits the flow pretty evenly. Furthermore, each of the outputs has a little flow control valve that lets you tweak the flows so you can account for different line lengths or different amounts of water for different pots. You just have to experiment to see how long you want to run the pump for. For me, it’s about 15 seconds which is probably a little on the short side; I sometimes end up watering a little every week or two. 

Now, in practice, actually building this was more complicated because of getting all the tubing sizes right. The big culprit was the pump. In order to get an aquarium/pond pump with sufficient head (pressure) you need to get one capable of vastly more flow than needed for this application. And because the pump is designed for that higher flow, its output size is fairly large so you need to adapt the tubing down to the significantly smaller diameter that’s appropriate for this application (and the manifold). I got it almost right; I had to use some epoxy paste in one place because I couldn’t find an adapter that was quite what I needed.

(There’s also a lot of inconsistency in how sizes are advertised, e.g. both the check valve and the manifold are supposed to be 3/8” but the tubing fits easily on one and was a very tight squeeze on the other. You may need to fiddle around.)

Finally, I added a check valve though it probably isn’t needed.

In addition to the parts listed above, here’s what you need:

  • Short piece of 3/4” tubing (I had some black pond corrugated pond tubing from earlier experiments)
  • You may need some epoxy paste if a connection is a bit loose connecting this tubing to the adapter
  • Multi-hose adapter
  • 3/8” tubing (probably ID)
  • Aquarium airline tubing (I believe it’s 3/16” diameter)

Finally I was trying to figure out what I could stick the pots in so that I didn’t need to worry if there was some overflow. I was coming up more or less blank. The options either weren’t really the right shape or they were a lot deeper than I needed or wanted (or both). Then I found the perfect thing: a 26” water heater drain pan. Just cover up the hole for the drain with duct tape. To make it even more perfect, I happened to  have a round 26” table up in my attic.

Now my herbs are happy and I’m happy. 

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