Optimizing for Plant Growth by Rotating Crops Frequently

This is a collegiate level entry for the Growing Beyond Earth Maker Contest.

I spent a couple hours of thinking through the design challenges and going through source material. Then, when I was reading about the lettuce's growth requirements, I noticed a section called 'transplant instructions'. That was my light bulb moment. If you can move the plants around, you can put them in a small space while they are small and move the plants to a larger space as they grow.

To show how this design will work, I have modeled the essential components in Tinkercad and screenshot key points for your viewing pleasure.

This concept requires constant rotation of plants in order to work properly. You'll want to have small, medium and large plants at any given moment.

Hexagons tessellate, but circles don't. You can fit more hexagons onto a tray than you can fit circles. If the plants are 15cm by 15cm, you can roughly approximate with a hexagon. If the tray is roughly 50cm by 50cm, you can fit 9 circles onto the tray, or 12 hexagons. When the plants are tiny, 5cm by 5cm, you can fit 100 circles but 114 hexagons (maybe more if I had time to squish them together better).

In this way, whether the plants are big or small, you can fit more hexagons onto a tray than circles. To reflect the growth of plants over time, I have modeled trays to fit 12 15cm squared plants, 27 10cm squared plants and 114 5cm squared plants

It seems reasonable to assume that these plants are to be grown in a sort of foam that soaks up nutrient-filled water. This foam can be cut into any shape, so I suggest cutting it into a series of small hexagons and a series of larger ones with holes in the middle, so they can be stacked.

This way, as the plants grow, there is no guesswork about how much extra space to give them. Just slide the first hexagon into the second, and the second into the third.

There are now three tray sizes, one for each stage of growth. We can use this fact to optimize height and stack as many plant trays up as possible. (For simplicity's sake, and because I've never taken calculus, each tray is represented as being it's maximum height in the pictures above.)

To begin the process, plant 114 seeds in the small tray, each in it's own little hexagon foam piece.

9 days in, examine the first 114. Choose the strongest 27 and plant them in the medium tray, using the transplant suggestion above. Eat the other 87 now. (True, they are not full size, but seeds are edible once sprouted. According to this article about sprouts by Penn State Extension, the biggest danger with eating sprouts is if the seeds happen to be contaminated. That's a risk you take whenever you grow your own food.) Replant the small tray with 114 more seeds.

18 days in, choose the strongest 12 from the medium tray, and plant them in the large tray. Eat the other 15 now. Choose the strongest 27 from the small tray and plant them in the medium tray. Eat the other 87 now.

27 (or 28, if you prefer) days in, harvest the 15 plants in the large tray, and move the others up, as detailed above. Replant the small tray. From this day on, by repeating this process, you will harvest 114 plants of various sizes every 9 days.

These are the maintenance pieces, the parts that make everything function properly: light, water and ventilation(Assume that the models above are shown from the back or the side).

Light is provided by 6 or so LED strips 4cm wide and about 50cm long (white strips in the model). These are mounted on the bottom of the water tank and beneath all trays.

Ventilation is accomplished with tiny computer fans (pink in the model) placed in the gaps between hexagons.

The wires and power supply are represented by black lines and a black box. Notice that the trays can be plugged in at any position in the box, and the power supply can be plugged into any tray. It is assumed that the fans will be on the trays permanently, since their function of keeping the plants from becoming too humid is vital to plant growth.

Water is stored in a 50cm by 50cm by 3cm tank (light blue in the model) at the top of the box. A small pipe runs down the side of the box, with places to plug in trays at every possible tray position.

What you might call the 'ideal rotation' may not always be feasible or practical.

If you are in a hurry, you can plant up 5 small trays, and eat the lettuce from 4 of them.

If you find that you do not need the full 114 seedlings to get 27 strong plants, you can half plant the small tray to save seeds.

If you plan to harvest the large plants, but let them continue to grow, you can keep 2 large trays, and harvest half of the plants every 14 days.

I am certain there are other configurations mathematically (2 mediums and a small, 3 smalls and a medium, etc.) but I cannot think of any other practical reason to include more possibilities here.