For many, the best watering system for orchids is the immersion of the pot. But I am very lazy: since I had a ouple of orchids, I have studied this automatic irrigation system for the windowsill.

The pots are watered with cyclical dives controlled by a timer. A watering cycle is adjustable in duration (flow) 1...60 minutes, and in repetition (ebb) from every 2 minutes to one every 14 days, to adapt to all needs. In the case of multiple cycles within 24 hours, the timing between day and night can be differentiated.

This project can also be used in hydroponics, for all types of plant, according to the method known as 'ebb and flow' (flow and reflux: like the tides).

The project criteria are:

Flexible project, easily modifiable and adaptable to different needs.
Availability of the parts; all the parts are very common and not critical
Simplicity and reliability of DIY operations
Low cost

We can consider this project divided into two parts:

containers: grow tray and reservoir
special timer for ebb & flow

The full project is in repository: https://github.com/msillano/Sonoff-ebb-and-flow

Step 1: Grow Tray and Reservoir

The practical problems for the DIY realization of the grow tray and reservoir are:

The support for the grow tray, which must be placed higher than the reservoir to take advantage of gravity during reflux.
The realization of the watertight joints between the pipes and the grow tray, in particular the inflow-outflow pipe, which should be realized as the drain of a shower tray to allow a complete emptying, and the overflow pipe to be height adjustable.

My choice fell on two transparent plastic containers, stackable, very cheap and 'food safe' (see note at the end). They have the characteristic of having a recess on the lid to accommodate the bottom of the upper container.

The 30 x 20 dimensions allow an easy movement and can contain from 3 to 5 orchids (a little narrow ... 40 plants / m² . recommended).

Obviously you can use different containers: the important thing is that the containers are stackable and that the lid has a recess.

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To read more: see orchis-sonoff-en01.pdf (versione italiana orchis-sonoff-en01.pdf).

Step 2: Sonoff Timer

Compared to mechanical timers, which usually have a resolution of 15 minutes, and a 24-hour cycle, this timer has a resolution of one minute, thus allowing very short periods of flow, and programming from many times a day up to a once every 14 days.

It can also be integrated into any Home Automation project that uses the MQTT standard, is simple to construct and has a ridiculous cost.

Note: Using a solenoid valve or a pump (up to 500 W) this timer can also be used for the programmed watering of gardens and vegetable gardens (see also https://github.com/msillano/sonoff_watering: another specialized timer for irrigation of the terrace).

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To read more: see orchis-sonoff-en01.pdf (versione italiana orchis-sonoff-en01.pdf).

Step 3: Notes

Notes on Ebb and Flow

The duration of the flow periods and the interval between two irrigations (ebb) depend on the plants and the substrate: the more the substrate retains the water, the longer the flow periods must be spaced....

Notes on Flower care

To control the health of the solution and the plants I use Xiaomi Huahuacaocao Flower Care (Mi Flora): a probe for light, temperature, soil moisture and EC. This probe can be used directly with a smartphone (Flower Care app) but it is also readable in MQTT environment with the miflora_mqtt_daemon software....

Notes on the safety of materials.

This project is intended for ornamental plants and NOT for human food plants. If you want to use it for salad, tomatoes, strawberries or basil, you must use all components "food grade".....

Notes on electrical safety

In the presence of electricity and water you must be very cautious....

To read more: see orchis-sonoff-en01.pdf (versione italiana orchis-sonoff-en01.pdf).