If you don't have electricity and water near the area to be watered or you don't want to use it because it is your second home and the taps are closed and the fuses are broken when you are away, automatic gravity drip irrigation can be a solution for a self-sufficient system, but it has some implementation constraints.
Having a water tank
Automatic gravity watering requires a rainwater reservoir or a tank filled regularly with water when you are present intermittently. Its volume will depend on your autonomy. A tank of one cubic meter is a good starting point and will ensure several weeks of watering depending on your surface to cover. By connecting several tanks you will increase this autonomy.
The advantage of the water tank in the case of a second home is to leave with peace of mind with the water meter valves closed. Who hasn't experienced a leak on his watering system?
Severity and pressure
In this type of watering, the idea is to take advantage of gravity to feed our drip system. Under its effect, the water will flow in your network which must be under the water level of the tank. In fact, a buried tank on a flat ground will not be suitable without a pump and therefore with electricity nearby.
But for the drip system to work at its best, pressure is needed to feed and distribute the water throughout the network. This is related to the height of the tank and more precisely to the height of the water level, placing the water tank as high as possible will be an asset. If your land is flat, you should consider raising the tank by a slope, a small construction, some breeze blocks or pallets, if your land is sloping, simply place it in the upper part of the garden.
The pressure is 1 bar every 10 meters vertically (editor's note: information well known to divers), a meter of difference in level between the tank and the watered area makes you gain 0.1 bar of pressure. This is only an order of magnitude, but it is important when it comes to solenoid valves.
To facilitate the flow, bring the water as close as possible to the area to be watered with large diameter pipes starting with 25 mm for example and then create a secondary network with 16 mm and finish with small pipes if necessary next to the targeted plants. The drippers can be installed directly on the secondary network or of course on the tertiary network.
Not one but many networks
Too many drippers on your network will not allow you to keep a good pressure in the whole circuit. Some branches may not be supplied. It is therefore important to define several networks operating at different times from the same tank to maximize the pressure and therefore the flow.
Create separate networks for different zones, depending on whether it is a vegetable garden, a dry rock garden, a flower bed, a hedge, etc. The watering times and frequencies will not be the same in any case.
Adapted solenoid valves
Solenoid valves are taps whose opening and closing is controlled electrically by a nearby or remote programmer.
Most of the solenoid valves available on the automatic watering market only work from a certain water pressure, generally between 0.5 and most often 1 bar. Be careful because this information is not always available on the technical data sheets or the packaging of the products on the market. It is unlikely that you will have such a pressure or your land is very steep, so you need to find 0 bar solenoid valves, which open without or with very little pressure. This is the case of some automatic programmers like the "tap nose" for automatic watering from rainwater harvesters. Moreover, some of them propose 2 ways, that is to say the possibility to program the watering of two different circuits. Most of them work with batteries, which is good because we don't have electricity!
Programming of the automatic watering
For a bed of flowers or a vegetable garden, a watering of approximately one hour every 48 hours in summer is a base of departure to allow a watering in depth and not just wet the surface ground. Then adapt according to the needs of your plants.
Consider starting at night when the soil starts to cool down after midnight. Distinguish and adapt the programming according to the seasons, so decrease the frequency outside the summer period by passing from 48h to 72h for example.
A drip irrigation system
With a low and variable pressure according to the level in the tank, and according to the altitude of the different circuits if your garden is not flat, an adjustment of each dripper is necessary. Also adapt the flow rate of the drippers to the needs of your plants. Over time, check that each dripper is working properly, as particles can clog them or even lime deposits can block them. Make sure that the tank remains clean and free of deposits.
Although it may be tempting to use other types of sprinkler systems such as boom sprinklers, their water consumption is not at all the same and will limit the life of your water supply. So use sparingly.
Last tips...
Place taps to purge air at the end of each of your circuits.
Connect several 1000-liter tanks together to gain autonomy depending on the space available for their installation.
Test your installation for a few weeks and measure the consumption in the tank. This will allow you to estimate the available watering time in your absence or to adapt the possible watering duration.
