I have my entire greenhouse irrigation system connected directly to a dual channel water timer that screws on to my water spigot. This timer is set up to go off once a day for each channel, on one channel I have my misting system to go off for about ten minutes while the other channel controls a total of ten minutes of drip irrigation. Now that the winter months have come, I simply reduced my misting system to five minutes every three days and my drip system to ten minutes every three days; all by the turning of a dial.
A few problems:
There are just a few problems with drip irrigation systems in specialized greenhouses. This mostly has to do with the nature of water intake of certain kinds of plants. For instance orchids are very keen on absorbing moisture from humidity, and pineapples have roots in between the leaves to catch falling water. In both of these instances, a consistent drip of water will not adequately spread the moisture to the entirety of the plant. For this reason micro sprinklers and misters prove to be vital tools for greenhouses growing plants such as bromeliads, orchids and epiphytes. These sprinklers come in many varieties, some have a directional sprays, others have a 360 degree rotation. They are great to set up in the corners of the greenhouse facing the plants, or in the middle of the greenhouse to ensure everything gets at least a little moist.
Planning your irrigation system:
There are many things to take into account before setting up your irrigation system. The first is, it is a lot of time and work, and even more fine tuning, before your greenhouse can water itself. Perhaps you would be more keen on watering yourself to ensure that each plant gets the amount of water that you know it needs. Second is cost, though the good news is that it's pretty cheap. Look at paying anywhere from $100-$300+ depending on greenhouse size, number of plants, and extra features. For instance, you can get a cheap water timer, cheap tubing and drip heads and totally skip the filter, pressure regulator, and the bells and whistles. It might not be a very effective system in this case, but it certainly gets water where it needs to be. Lastly, you should consider a rough plan as to where to run your irrigation lines. Traditionally the mainline is buried underground or is ran above ground with the drip emitters coming up into each pot. The latter method is a little easier when growing in ground beds, but I find it pretty chaotic in a potted greenhouse. Therefore I chose to zip-tie my mainline to the frame of my greenhouse just a few feet above the ground. This allows easy access to the mainline to add new drippers and check for leaks. So figure out where your spigot, or water source is, plan out approximately the length of mainline needed and how you want it to run through your greenhouse.
Once you have figured out roughly how much drip line is needed, you can move on to planning how many drip heads you need to buy. The first thing to keep in mind is that not all plants require the same amount of water, luckily there are drip-heads for nearly every water requirement. Common flow speeds are usually measured in gph (gallons per hour) and include 1/2 gph, 1 gph and 2 gph. There are some heads that have adjustable flow, allowing you to change the water flow as the plant grows or as conditions change. I highly recommend these adjustable heads for larger plants such as bananas, papayas, etc. so that you can increase the water flow as the plant's demand for water increases.
Here's a short list of irrigation parts and what they are used for:
Dripper/emitter: These are the plastic fittings that you can attach to mainline or emitter line to regulate water flow to plants. They come in different flow speeds, so make sure you get the right ones.
Mainline: A pretty self-explanatory name, this is the black tubing from which the secondary (1/4") drip line will branch off from. There are two sizes of mainline available. A hole puncher tool is typically used to puncture the mainline and insert the plastic fitting connecting it to the drip line.
Fittings: There are a wide range of fittings available for drip irrigation systems, these include elbow joints, end caps, tee joints, hose adapters and more.
Filter: A filter is a plastic piece which fits between the spigot and the beginning of the mainline, inside of this piece is a mesh designed to filter out any small particles that may be present in the water supply. This ensures that the emitters won't get clogged with debris.
Stakes: These come in many sizes and their purpose is simple; to keep the tubing in place. They are very useful for ensuring that emitters stay in pots.
Pressure regulator: Sometimes water pressure can be too great for irrigation systems, this is where pressure regulators come in. A pressure regulator is attached in between the spigot and the mainline to ensure that the pressure from the spigot doesn't surpass a set limit.
There are other irrigation pieces available to make greenhouse gardening even easier! These include fertilizer applicators, mister heads, foggers, sprinklers, and more.