Kristof Goossens

I’m currently trying to grow Stevia plants. It’s supposed to be hard to do from seeds, but the plants aren’t for sale here and the incredibly sweet-tasting sugar leaves make it one of my favourite plants. They are not cleared for consumption in the EU and US (google for the conspiracy theories that the artificial sweetener industry is behind that) but you can use the dried, crushed leaves in the same way as sugar.

Of course, since I want to maximize my chance of success, I’m doing it the scientifical way. I have used four different kinds of planting medium and they are kept in a greenhouse under identical circumstances. The seeds cost about €5 for ten seeds. The pots are watered only on the first day and are kept moist in the closed greenhouse after that. The four kinds of planting medium are:

1. Asef Osmocote (the osmocote keeps 30% more water)
2. DCM seedling and young plant earth (stekaarde)
3. No-name generic cheap earth from a local gardening center
4. Coconut fiber peat.

Results

After three days, the first leaves are visible in the Asef Osmocote.

After four days, the DCM stekaarde seedlings have begun to sprout leaves as well.

After six days, the no-name earth started producing a pair of petals, but only a few days later they started rotting away and disappeared. The coco peat failed to show any results at all.

After one month, the plants range from 2 to 7 centimeters in size with six leaves on every plant.

Introduction

I like edible plants, I like electronics, I am no good at gardening. There is however a cool device called the aerogarden which combines all these things into one. It’s a table top system consisting of plant lamps, seed pods, tabletop holder, water pump and timers. The lamps are swiched on and the plants are watered automatically to ensure maximum growth speed. The downside is that the lamps and seeds are proprietary and you have to buy them from the aerogrow company as there are no alternatives which will fit. Unfortunately, it isn’t for sale here in Belgium and even if I could obtain the original, there is no way to get the seeds and replacement lamps afterwards.

Requirements

So the original is out of the question, but it seems to work very well and the principle is sound. When you come to think of it, it isn’t hard to construct your own model, so that’s what I set out to do. I don’t mind the initial investent cost, but I did want to keep the running costs as low as possible, so there were a number of changes to the original.

•  Closed greenhouse type. To maximize germination speed, I wanted to raise the temperature for all plants. Instead of the individual plastic domes, i opted for a large plastic dome over all plants together as found in germination sets.
• Added cooling. In order to prevent the plants from overheating, I added an active cooling system capable of pulling fresh air from the outside and replacing the hot air on the inside.
• Solar-powered. In order to minimise the running costs, the lamp, cooling and water pump must all run from a 12v solar powered system so that no external electricity is used. I will be using two LED 12v bulbs, a 1 watt red one and a 0.3 watt blue one. Total power consumtion per hour = 1.3 watt. I want to power it for up to 24 hours so that is 24*1.3 = 32 watt total storage. A 3.2 amp 12 volt battery can store 38 watt so that gives a little extra capacity. The lamp doesn’t have to be on during daytime so 24 hours is about three days capacity. An estimated 5 hours of direct sunshine per day on a 2 watt solar panel should give 10 watts per day of charge (very rough estimate as the panel also charges in the shade)
• replacement of timer system by switch and direct solar drive. The greenhouse heats up when the sun shines, so the fan to cool it must only be active when there is sunshine. This means that it can be direct driven by a separate solar panel.
• Replacing the proprietary seed pots with Jiffy tablets. I really like these because they are clean, self-regulating for water, compact to store and you kan transplant the entire plant with the jiffy pad attached to it later on as the roots can grow trough it.

Components + price

Most things can be found at the local hardware or DIY store and the gardening centers; For some special items I went internet-shopping at conrad electronics and 1asolar webshop. The following is a list of everything I got to experiment with.

Construction

(more details and illustrations to follow later on)

1. Dremel out the fan enclosure
2. drill holes for the cable holders and light fittings
3. Attacht the lamps and fan
4. Mount the electrical connectors
5. Attach the Solar panel to the fan
6. Attach the second solar panel to the charging controller
7. attacht the light circuit to the charging controller
8. attacht the charging controller to the battery
9. Put the jiffy pads in the grow box and let soak in water
10. Put the seeds in the pads and add fertiliser if desired
11. Wait till the plants start growing :)

Resulting video

Youtube