OK, so this week, I have been working to build a complete system design for Next Door Farms. I already knew that I am going to have to build these growing systems out in stages, so that makes the design process a bit more complicated. I need to know where everything is going to ultimately go, so I can make sure to install water and electrical supply as needed, and so that I can pre-dig all buried pipes before installing any components.
Since my greenhouse will measure 30’ wide by 100’ long, I have envisioned an ultimate system that will produce weekly Harvest Boxes of greens (2 types of Lettuce, and 3 various greens – Arugula, Mizuna, and Italiko Red to start) and Fruiting Boxes that will include tomatoes, cucumbers, eggplants, and peppers to start). Due to the time of year that I am going to begin construction, and the constraints of my initial budget, I am limiting my initial phase to only the Greens boxes for this Fall.
So, how can I determine what is needed for the Greens boxes, and how many I will be able to produce. Let me walk through the numbers a bit. I know that I want to produce a Harvest Box that contains five items. My current plan is that this will be two heads of lettuce and three bunches of other greens. The first thing that I need to consider is spacing. Lettuce really needs to be planted at a 6” spacing for a full-size head. The other crops (Arugula, Mizuna, and Italiko Red) will do fine at a 4” spacing. The floating rafts that I will use for the DWC troughs will measure 4’ long by 2’ wide and will have holes cut in them to make the proper spacing. This will translate to a 28-hole raft for Lettuce (6” spacing) and a 36-hole raft for the other crops (4” spacing). The second concern is the growth period for each crop. All five of these crops have similar growth cycles, so that does make things a bit easier. But the time to harvest in Summer is very different than in winter due to both temperature and available lighting (I will NOT have the budget for supplemental lights!) So, to ensure consistent production, I need to make my plan for the slower-growing season and account for extra production in the Summer. Right now, I am planning for a 5-week growing cycle in the Winter to be on the conservative side. After growing through this winter, I will look at the results and see if I can move to a 4-week cycle and produce a few more boxes next year. Right now, this means I will need 5 rafts for each of my chosen crops, or 45 rafts total. Specifically, I will need 10 rafts with 28 holes for the two types of lettuce, and 15 rafts for the other three greens.
Now, to think about the DWC trough itself. I have a roll of food-grade liner that is 100’ long. The trough will be 4’ wide, and 1’ deep. That means that the absolute maximum length I can do is 98’. I like to make build on the safe side, so I will plan a 96’ length. This will give me a total of 48 rafts in my first DWC trough. That fits with my crop plan above, and I can use the extra three rafts for some experiments or just overflow as needed.
So, to review, from a single 4’x96’ DWC trough, I “should” be able to produce 28 Harvest Boxes weekly, though I will plan on 25 simply to allow for any inconsistency in plant growth or other crop issues. With this plan, each box would contain 2 heads of lettuce, and one bunch each of Arugula, Mizuna, and Italiko Red.
To maximize the profitability of the farm, it is vital to balance the productive capacity with labor efficiency. For this, I mean that there must be enough room to walk around easily and to roll carts, grow seedlings, and harvest/pack boxes. Additionally, the Greens Harvest Boxes will be the “bread & butter” of this farm initially. Therefore, I have a goal of trying to produce 75, or more, of these boxes a week when at full production. With this goal in mind, and after playing with multiple possible layouts I have decided on the system layout shown in the image below.
I have roughly split the greenhouse in half, one side will be DWC troughs, and the other side will be Bato Bucket systems for fruiting crops. On the DWC side, if I can produce ~25 Harvest boxes from my initial trough, then I will need the equivalent of 3 DWC troughs to reach my goal of 75 weekly Harvest Boxes. To save a slight bit of space, I have decided to build one 4’x96’, and another at 8’x96’. This will give me the same production but will save nearly 2.5’ of floor space because I can eliminate a footpath. The other side of the greenhouse will have the Bato buckets, right now I am planning on three separate systems. Each system will run about 80 feet long, and the buckets would be spaced about 2’ apart. Two systems would have about 80 buckets each and the third would be almost 40. The open space at the end (~15’x20’) would be used as a transplanting/harvest area and storage for daily-use items.
The DWC troughs will all be connected as a single system. This is because all the greens crops will grow effectively on a single nutrient solution recipe. I can simply run an airlift system to move the water through the troughs while providing both aeration and circulation. With this design, I will also not need to dig a sump tank into the ground which would take up valuable floor space in my greenhouse.
The Bato Bucket systems will need sump tanks, but one benefit of this system design is that the sump tanks can be installed directly under the buckets themselves at one end of the run. All the crops grown in these systems will require slightly different nutrient recipes for optimal production, so that is my thought for having the three systems. Additionally, since these are all fruiting crops, there will be a cable system installed above the buckets to allow for easy trellising of individual plants.
I am going to spend the next week refining this design and drawing up a blueprint that I can use to create a material take-off list for each system and each phase of construction. I know that there will be additional aspects I need to contemplate - like harvest areas, pack & prep tables, storage, and more. I will have to think about those details as I draw up a formal blueprint.
Before next Saturday, I will also post another article that details my thoughts on this model, and why I think that it will be financially viable, replicable, and could be extremely valuable to the Urban Agriculture movement nationwide.
I'd enjoy talking shop with you (during you're quiet time, as I'm in Canada, so no rush❄ ;).
Would really like to set up an efficient greenhouse to offer "Greens Harvest Boxes" like you!
Leafy greens are my favourite quick crop, but this winter I'm just growing for the 2 of us (indoors).