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I would like to use a drip irrigation system for my houseplant, for fun and to hopefully go from watering it daily to maybe checking up on it weekly. I don't want to deal with connecting it to my actual plumbing, so I want to use a large water tank as the water supply. In my mind, I should be able to set it up so that so long as there some amount of water left in the tank, it will deliver water at a constant, very low rate to my plant. Whenever I see the water level get too low I can refill the tank (which should be once in a couple days or so). This implies that I must somehow keep pressure constant, I think I can set up an intermediate water reservoir with constant water level using a floater valve, or I can just connect a very low pressure regulator (I've found a cheap one that is 5 PSI).

After shopping around for emitters, regulators and valves, however, it seems like all the readily available parts are designed for scales much higher than what I want:

  • My plants seem happy with about a liter per day (possibly less) and the smallest emitter I've seen is 0.5 gallons per hour.
  • Common PSI ratings for the emitters are 50-60 or so. Even the mini emitters seem designed for close to 15 PSI. In order for me to provide 15 PSI through gravity, the water column would have to be many meters high, which seems impractical.
  • Based on some simple calculations, I find that if I just punched a hole in my tank, even with a water depth of just 10 cm, I would need a ~50 micron hole to drip water at 1 l/day. This is obviously beyond my limit to construct precisely.

It seems like I need either a very low pressure regulator (<1 PSI), a very low rate emitter which operates at low pressure (order of 0.1 PSI) and provides a very small flow rate (order of 0.01 GPD), or an adjustable emitter that can be accurately set to tiny fractions of its maximum. I suppose another option is to find a valve that can be precisely opened so as to have a defined, micron-scale aperture (which I suppose is what a dripper is, in a way).

Closest thing I was able to find was this: https://www.homedepot.com/p/Elgo-Planters-Drip-Kit-12-Dripper-Set-ELCDK12/301617796 The description is unclear about the minimum pressure and how tunable it is, but it does claim a flow rate of 0.35 GPH, which is somewhat close to what I need. But I don't understand how much less than 0.35 GPH it can do.

Just to be clear: my question is of a purely practical nature. I know people set up drip irrigation in larger gardens, greenhouses and fields all the time and the components seem to be readily available. Surely if it so easy to do with larger flow rates, setting up a miniature version with low flow rate must be no problem, but I can't figure out how to get the flow rate down to the level I need.

I know I can use a timer or electrovalve, but I'd like to keep this project purely hydraulic if possible, out of personal preference.

I haven't specified a plant because I feel like if such a system is set up properly, it should be very easy to tune the exact amount delivered. Then I can adjust it depending on my needs. In fact the ability to precisely control amount of water is part of my motivation.

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    You may think this is off topic, but what is the plant and is it one that doesn't like the standard regime of being allowed to dry out slightly between waterings (meaning watering might be as little as once a week)? – Bamboo May 1 '18 at 18:40
  • We have to know what plants you are trying to water. Everyday? Are you growing rice? Plants, especially indoor plants never need watering everyday. I would never automate watering indoor plants. Each plant is vastly different in needs. Its needs different from the other plants affected by its environment in the home. Watering everyday is a problem and automation is not the answer. What soil have you used in your pots, what are the types of plants you are watering, did you put rock or gravel beneath the soil which I hope is potting soil? Bamboo and I can only imagine watering 1X/wk... – stormy May 1 '18 at 21:50
  • @Bamboo I think I see what you're saying, but I guess my interest is in building a system that can deliver water at a user-adjustable rate to any plant. – Proseet May 2 '18 at 3:36
  • @stormy Well, I tried to simplify in my question for clarity, but this is actually a small flowerbed outside my window (but I can't/won't set up a traditional sprinkler system). There's several plants (strawberry, tomato, potato, etc), they change somewhat depending on what I feel like planting, and they've done well in the past with about a liter a day. I guess it's hot here so the water evaporates/seeps away into the ground. If I had a drip system set up, I could dial down the rate and possibly avoid over watering. – Proseet May 2 '18 at 3:40
  • What is the size of this flower bed outside your window? Sounds as if you have a 'planter' which is the same as a pot. What soil did you use? What did you grow in this soil last year? Watering every day might be okay during the heat of the middle of summer but now? Really need to know the size and amount of soil for tomatoes, potatoes and strawberries. What do you mean flower bed? It would be nice to help you to get set up so you do not have to water every day. The fact that the soil stays wet means disease, fungus. If this is what you grew last year...? We can talk about that... – stormy May 2 '18 at 5:06
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You might be interested in a gravity feed auto-watering system. I use a float-valve watering system comprised of a 3.5gallon bucket inside a 5gallon bucket with a siphon feed into a garden olla. https://youtu.be/iSxSccEdXWw

This system works for my indoor/outdoor hydroponics as well as my raised beds. Your application is similar to my raised bed but smaller. Plants draw water from the soil. The soil hydrates from the buried olla. The buried olla replenishes from the float valve system. Such a system works, but requires two buckets and one olla per watering site. It would work for potted plants, but you would need narrow and deep ollas to fit in the pot. I would invite you to consider a simple indoor Kratky setup for watering your plants, in which case you don't need the olla and can simply put the plant in a 3.5 gallon hydroponic bucket fed from the float valve system.

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