Inexpensive Plant Propagation Mist Controller

This is an improvement over my previous Plant Propagation Mist Controller Instructable. While I am still using that relay module and I have been very happy with the performance of it, these other relay modules are cheaper, more readily available, easier to program, and have a better display. If you are new to homebrew mist controllers I still recommend you peek at the original instructable though as it does work.

In this project we deal with electricity and water. I'm not an electrical engineer and none of this was tested by UL. If you are unsure about how to safely set this up, please consult a knowledgeable professional. I am not responsible if you electrocute yourself, burn down your house, or suddenly decide pineapple is a good pizza topping. Please exercise caution and common sense. The timer module and wall plug are not waterproof and must be enclosed in a protected area to avoid short circuiting.

So let's talk about what we are building here...

Mist propagation is a method of plant propagation, most often cuttings but sometimes seeds, in which a fine mist of water is sprayed frequently over the propagation area. The advantage of this is that when you take a cutting, you have seperated that part of the plant from the roots which were supplying water to the plant tissues but you still have leaves which transpire and lose water. By keeping the leaves and stems misted, you significantly slow this water loss and allow time for new root formation.

The biggest challenge with this type of system is the timing. Unlike traditional "irrigation" timers which are designed to allow the flow of water for several minutes at most a few times a day, we need a timer capable of allowing water flow for only a few seconds every few minutes continuously throughout the day. These type of timers are commercially available as well as electronic leaf devices which negate the need for a timer but they cost hundreds of dollars and for the backyard hobbyist are a huge barrier to entry on setting up a mist system.

What I have come up with is a repurposing of inexpensive "timed relay modules" which you can think of as programmable timed switches. They turn the switch on for a set time then off for a set time and repeat infinitely. That switch is then wired to a standard irrigation valve which is what will allow water to pass to the misters. The advantage of this type of controller is that they are cheap. Really cheap. Five US dollars a piece shipped to your house cheap. If you are a professional and need high quality and bulletproof reliability, I highly recommend you look at commercial equipment. This instructable is aimed at people who just want to play with this in the backyard and will not be financially devastated if their ridiculously inexpensive timer fails and lets the cuttings dry out.

So what parts do we need?

Step 1: Parts

There are only really three parts to the control system. By controls, I mean the parts that turn the water on and off. You will require additional parts to get the water from the spigot to the valve and from the valve to the mist nozzles but because every situation is different, the scope of this instructable is only about the control circuit.

The Timed Relay Module This piece is available all over eBay from various sellers. This is who I ordered mine from and the shipping was pretty fast (by "shipping from Asia to the Eastern USA" standards). EDIT: A fellow plant propagator found this on Amazon for a little more money but a lot faster shipping.

Irrigation Valve I used a 1" but a 3/4" valve should have plenty of flow for a reasonable sized mist bed. The link I provided is to an Amazon listing but your local big box hardware store sells these in the plumbing section (at least seasonally).

12 Volt, 2 Amp power supply While writing this I noticed my link from the previous instructable is already a dead link. I have no idea how long this link will stay good for but any 12 volt, 2 amp power supply should work. [TECH NOTE: The solenoid in my valve draws about a quarter of an amp when open and the display and timing circuit have some draw as well. In most applications a sub-one-amp power supply would probably work but since there could be variance in current draw between valve manufacturers, a 2 amp power supply is what I suggest for general use.]

A little extra wire. Pretty much any insulated copper wire will work.

Step 2: Wiring It Up.

This graphic shows how I have mine wired up. You could use the relay to switch the negative (as in the eBay seller's example picture) but I wired mine with the positive being switched. Electronically, I don't think it makes a difference. The image is crudely drawn and obviously not to scale.

Depending on what valve you buy, the two wires coming out of the solenoid may have one red and one black, one black and one black with a white stripe, both black, or something else. It doesn't matter which way you hook the wire coming from the switched side of the timer and the power supply as long as one is positive and the other is negative.
I'm not sure what the maximum allowable length of wire from the controller to the valve is but I suggest keeping it as short as possible. I think mine is about 5 feet of wire.

The power supply and timer module are NOT WATERPROOF. I use a small tupperware container with holes in the sides for the wires to enter and leave to protect mine. It isn't perfect but it has worked so far. If you are creative enough to build a mist bed, you are creative enough to weatherproof the timer.

Step 3: Programming the Timer

Here is the Instruction Manual from the seller, I will edit with better instructions later but you should be comfortable pressing buttons and playing around with the controller.

1.After setting the data, you must wait 6 seconds,6s post modules automatically save memory set data.

2.Press SET key once to enter the time setting mode,the red LED flashes, press the key to increase or decrease the setting time T1.

3.After setting time T1,short press the SET key again, the green LED flashes,and the time is set by pressing the key Time T2, T2 time setting is completed,press SET key again, the system will automatically save the memory setting time or wait for 6s, 6s module will automatically save the data memory.

4.Long press SET,enter parameter setting mode.There are two sets of parameters for the user to select P0, P1.Short press SET in the current mode to switch between P0 and P1.

5.In P0 parameter can be set by pressing the key to adjust their own timing mode.In the P1 parameter can be set by adding and subtracting keys work mode.P0--0:T1 Timing mode is second.P0-1: T1 timing mode is minutes.P0--2:T1 Timing Time mode is hour.P1--0:Delay T1 time,relay pull(T1 timer)P1--1:Relay release after T1 time delay (T1 timer)P1--2:Delay T1 time,relay pull(T1 timer),and then relay release after T2 time delay(T2 timing),then it is finished.P1--3:Relay release after T1 time delay(T1 timer),then delay T2 time,relay pull(T2 timing),then it is finished.P1--4:Delay T1 time,relay pull(T1 timer),and then relay release after T2 time delay(T2 timer),cycling.P1--5: Relay release after T1 time delay(T1 timer),then delay T2 time,relay pull(T2 timer),cycling.

I program my timer for 2 seconds on, 400 seconds off, repeating. The timing needed on your setup may be dramatically different.

Step 4: Setting It Up

Note: Garden hoses are not designed to hold pressure. If you need to run water from your spigot you need to use pvc pipe or get hoses rated for constant pressure such as the stainless braided hoses used on washing machines.

I'm not going into great detail as there are many other, better sources out there but I will give a brief overview of typical backyard system setup.

Female hose coupler to PVC pipe (1/2 or 3/4") to get the water close to the desired misting area. An extension cord can also be run to get the power there as well. The pipe or hose get plumbed into the inlet side of the valve. Most valves have an arrow indicating direction of flow but the solenoid where the wires come out is always on the outlet side. Once the valve is plumbed to the supply, you can use more pipe or a short length of hose to get the water from the valve to the PVC misting manifold. This is simple an arrangement of PVC pipe with the misters installed at an even spacing. I use three 7GPH mist nozzles spaced about 24 inches apart and raised up about 10 inches. Your number and arrangement of mist nozzles may be a lot different. When you buy mist nozzles make sure to order extras as they clog easily and you don't want to have to wait on replacements. I drill and tap threads directly into the PVC to mount my misters but you'll find there are many ways of mounting misters depending on type.

For much more detailed and visual representations of setting up and using a mist bed I recommend Jim Putnam's HortTube on youtube, especially this series and later this one too.

Step 5: My Mist System

This brief video shows a broad overview of how I have my mist system setup.

I use a shade cloth over the top and landscape fabric on two sides to minimize wind and offer some protection from direct sunlight.

I have a removable drain plug at the far end of the mist manifold so it can be flushed out or drained as needed.

I have three risers with the mist nozzles at the tip of each. I drilled a hole in the PVC endcap and tapped it with threads so my mist nozzles just screw in and can be unscrewed easily for cleaning or replacement.

As you can see I have a variety of different random cuttings from Rubus ulmifolius (thornless blackberries) to setcreasea (purple heart vine).

As the camera continues to pan across you can see that it is plumbed with PVC until it disappear behind the groundcloth and potted plants. It actually connects to a stainless braided washing machine hose back there.

Ignore the potted blackberry plants.

You can see the silver hose comes back in and is connected to the irrigation valve which is connected to a Y splitter on my hose spigot.

The small tupperware box is what protects the controller. I drilled small holes in the sides to run the wires out. In this video it still contains the controller from my previous instructable but the function is the same. I ran a common 3 prong extension cord in one side and run the two wires out to the vale out the other. So far this has worked well and only cost about a dollar.

There are many great youtube videos with much more in depth looks as the specifics of other people's mist bed setups. I would suggest anyone looking at building a mist setup spend some time looking at what others have built to get ideas for what might work for you.