Plant lighting and automated care

I’d like to do a concept testing/idea bashing on a system of gardening (like a Growbox or a Garduino) with Led lights coupled with Arduino for the program execution (such as automated lighting and the control system).

There are examples of previous builds by plant enthusiasts which were experimenting with automation so it is nothing groundbreaking so I want to turn the challenge up a notch.

The issue it that I’d like to create a program/structure that can survive and be autonomous for long periods without care or inputs (in my case the 2-3 weeks where I’m out for work sometimes) and I’d like to test something new as an alternative to give it away or let it wither. Also I wonder whether I can activate a “combination” of leds, red-blue-white in order to reduce electric consumption given a specific plant and the stage it is in (I know it is complicating things but it is a more modular concept that once done I feel will simplify the whole process afterwards for the people who want to work on this project – in an open source kind of way)

I know we are entering spring but, as I live in a cold environment, Northern Europe, it is impossible to put it in the open (alternatively this can be used also by people during normal winters).
I close all entries to my house (that includes windows) but I keep the electricity on (for the alarms) thus I can still keep the system on for my plants. I’ve seen that there exist method to give “automated” watering that are simple enough to work for that period so it all comes down to a long (given the usual daily input that people put into the plant-keeping) programming setting or would you guys think that something else needs to be taken into account?

The Leds would be mounted to a PC CPU heat sink and the container will painted on the inside as white (non-gloss probably to increase reflection) which provides additional light diffusion to spread the light through the entire growing area.
Given offline suggestions, a soil moisture sensor makes sense to me in order to wiggle a bit on the first months of data and to get a bit more scientific bases on the elements to change (but this comes afterward).
I might also build a pH probe and fine-tune the soil acidity for different plants (but that will be decided on your first feedbacks as well) and add a relay-controlled heater to keep it within a desired set of temperature.

I will be testing it before leaving so that I don’t find myself a burned down apartment when I return.

Potentially I asked a bit of help from a couple of botanists as to create a modular type of thing; you put in the plant, the stage it is in and the time you will be away and the program sets the optimal amount of light/activate the best composition of Leds to reduce energy and water consumption (also given that a couple days ago was World Water Day) while giving an improved environment where the plants can grow and flower while not cared for by people at all times.

The question is: Is it feasible? Can the hardware support this kind of complexity (and which, in your opinion would be the most cost efficient one to use)? Can the software be done or is it a fool’s errand?

P.S. I know wifi control just makes things more complicated but I would also like to know it if that would be feasible given enough effort (to check while away).

Any suggestion will be highly appreciated. Thank you all in advance

If I understand, you want to do what the marijuana farmers do.
create a fully automatic system that operates without intervention until some future time.
the pot farmers on here know that they cannot attend to their crops, it is a plant and forget option so there is no way to get followed to the fields. put in at the beginning of the growing season, come back to harvest 6 to 12 weeks later.

an arduino can water plants when every they are dry. very easy.
they can time lights to be on based on hours on and hours off. not sure if plants care about hours off or not
heat is simple, there are lots and lots of heaters you can buy, or build.
I would say that a small fish tank with fish tank heater could do the thermal mass thing to delivery warmth without need of an arduino.
use that water to water the plants, fill it when it gets low.
seems like a simple project.

all that and a web cam so you can look in and ten adjust timing, fertilizer or whatever.
you could even raise the lights as the plants grow.

I start off by thanking you of your input,
I did not know that the marijuana producers had similar issues to that of many plant growers, given the value of the "production" in their sense I thought that being away for long periods would put the end result in great peril.
Anyway, getting back at the original topic, the program can be made so that I can input 21 daily programs and then let the program cater to the needs of the plant for 3 weeks (or even better let the program decide the "dosage" of light and water based on the sensors and data)?
Thank you again for your (and anybody who can/will contribute) help.

Something to keep in mind in your design - here in my area (Seattle), there are a number of requirements as far as what you have to have for protection if you have built in sprinkler systems (for watering the lawn etc.). They require you to have a double check valve "backflow preventer" in the line under most conditions. It actually makes sense - the intent is that if there is a fire down the street for example and the firetruck is pulling LOTS of water from the hydrant, it is possible to get the pressure very low or even negative in the surrounding houses and they want to make sure that nothing that could have any chemicals (fertilizer, weed killer etc.) near it could get sucked back into the system. Something to keep in mind if you are using control valves to provide water from your house supply to plants etc.