As cold weather approaches and our outdoor gardens start getting hit by frosty temperatures at night, many of us are contemplating ways to lengthen the growing season to keep producing food well into autumn. Although there are some decidedly simple methods of doing so, such as the use of row covers, low tunnels, or individual cloches, this geodesic dome is a great example of combining quite a bit of salvaged materials, a small amount of DIY electronics components, and what looks like a serious investment of labor to create a walk-in greenhouse complete with an Arduino-controlled irrigation system.





According to Mikkel H Mikkelsen, a 25-year old industrial design student, this past spring he "felt like taking a break from a busy city life and getting my hands dirty," and decided to try his hands at building a small greenhouse and growing some food. Thanks to his aunt and uncle, who had recently bought an old farm, Mikkelsen was able to use space in a horse corral and barn on the property to build his project, while also living rent-free in an apartment on the grounds, which enabled Mikkelsen to spend his funds on the greenhouse project instead of rent.





The dome's framework is built from pallet wood that was salvaged by Mikkelsen's grandfather, and this 'free' wood could pose a significant cost if it had to have been purchased new, but because of the salvaged materials, he says he was able to build the entire project, including a small chicken coop, for about 3,000DKK (€400 / $475). The measurements of the dome that Mikkelsen built aren't specified in his Instructable post, but he links to a dome calculator website where he was able to plug in the desired size, dome geometry, and other variables for his project in order to get exact measurements for all of the framework pieces.





Cutting all of those many frame pieces to exactly the right size required a table saw and router, neither of which Mikkelsen had access to, so the first step was to build a saw/router workstation using "an old handheld circular saw," after which he was able to start making the many cuts necessary (6 per piece) for getting the frame pieces ready to assemble. Each frame member was coated in linseed oil paint to preserve the wood in the humid environment of a greenhouse, and then the framework was assembled in sections. Although there are many creative methods of joining dome frame members together, Mikkelsen chose one of the simplest, pre-drilling and nailing the joints together with a mix of short and long nail sizes





Once the framework was together, Mikkelsen used a transparent rip-stop tarp to cover the sections, which he said "was cheap and did the job remarkably well," as compared with the expense and challenges of using glass pieces to fit within each triangle. To ventilate the structure, he integrated five windows into the covering of the dome, each of which is operated using automatic greenhouse window openers to keep the inside of the dome at a temperature conducive to plant growth.





Planter boxes were built around the wall within the dome, and initially an aquaponics system using a 2000 liter water tank took up the central space, but Mikkelsen ended up swapping the aquaponics system for more traditional grow beds, because he said the system needed too much of his attention. Watering the growing beds is taken care of through a gravity-fed water catchment system, and the distribution of the water happens through a drip irrigation system that is managed via solar-powered electric valves controlled by a "simple Arduino system."





Although the details of the Arduino system aren't listed in the Instructable, Mikkelsen said it was a large project on its own, because of his limited experience with the platform, and yet he was able to create an automated system that triggered "different events at different times of the day, based on a variety of inputs." The system includes a GSM module that Mikkelsen can use to communicate with the system via SMS, a potentiometer for manually varying the watering levels (by +/-30%), and a speaker that is triggered on entry to the greenhouse, which "tells me of the greenhouse status."



