Tiny Seedling Starter

I got into hydroponics, and I wanted a handful of very small seedling trays so that I could experiment with different nutrients to see what was going to work best for my system.  It was the middle of winter with our winters being quite dry I knew that I'd need to be able to keep the humidity higher around the seedings to avoid the starter medium drying out too quickly, but mostly because I'm lazy when it comes to remembering to stick to a watering schedule. 

I designed this little box to be able to fit the limited shelf space that I have, and to keep my experimenting down to a manageable size without taking over the entire house. I use those little Rockwool starter cubes, but you could also use cotton balls or some other medium if you prefer.

I print the lids and the vent covers out of a translucent filament which lets enough light through for the seedlings to grow.  I've found that with PETG, you can make the top of the lid clearer if you print really slowly and use the setting that ensures all of the infill prints in the same direction (in OrcaSlicer, disable the ‘Rotate solid infill direction’ setting). Print the vent cover separately and it will snap permanently into its spot on the lid so that you can control the humidity as the plants start to germinate

For the base tray and the optional inner platform, I prefer to use an opaque filament to discourage algae from taking everything over too quickly. You can use the platform to give space for roots to grow, or omit it to give the seedlings more room to sprout. The lid can also be easily modified in the slicer to increase the height if you want to allow for taller seedlings.

For my slicer settings, I printed the pictured models using a 0.4mm nozzle, 0.2mm layer height, 0.6mm line width, with no infill or supports needed.

To use, flood the tray until the water level is high enough that it keeps the growing medium damp, but not drowning. Pop your seeds in, add the lid, close the vent, and let the seeds do their thing. When you see the first leaves start to arrive, keep in a well-lit space, and keep the vent closed until the seeds can stand up on their own.  If you add artificial lighting, keep the lights close to the plants to keep them from bolting towards the light, but far enough away to avoid melting the plastic lid.  When it's time to remove the lid, let the seedlings get used to living in open air for a little while. A very gentle oscillating fan can help to strengthen the seedlings before they are ready to be planted or added to a hydroponic system.

I hope that you find this as useful as I have.