These are sprout trays and a tray extension for the 4-Tray Seed Sprouter by VICTORIO as seen on Amazon.

This was printed in PETG plastic with a 1mm nozzle, a 0.5mm layer height and two perimeter walls. This makes the wall thickness about 2.4mm thick, so it is very strong. I printed 5 bottom layers to make it 2.5mm thick and 0 top layers with 0% infill to make it hollow. If you want an extension instead of the tray, just print with 0 bottom layers like the top and you will have an extension. If you under extrude your tray prints just a little bit around 5% or so, they will seep very slowly which is perfect for this application. You don't want them to be completely water tight. If you find they don't leak enough, you can drill 1mm holes in the bottom to help the seeping. If you have never printed with PETG, it is a thicker more viscous plastic, so reduce your print speed by about 25%, unless you have a BondTech geared extruder that has tons of torque. The temperature should be between 235-250C. If you go above 250C, the plastic may start to outgas and form tiny bubbles in your print. The printbed should be 70-75C. If you are printing an extension, add a 4-6mm brim to help it stick to the printbed. I also use Aqua Net Extra Super Hold Professional Hair Spray Unscented 11 oz to help it stick to the bed. Put the hairspray on as thin as you can and wipe it very quickly with a paper towel before it dries to spread it out over the whole printbed glass. If you can see the hairspray, you've put too much on. It won't affect your print, it just wastes the hairspray. One super thin invisible layer should last about 10 prints before you have to respray, IF you let the glass cool off to 40C before trying to remove your print. Otherwise, a lot of the hairspray will come off on your print and you risk taking flakes out of your glass.

Found 13 3D-models for “Starter Tray” across many websites

Seed Starter Tray Insert

Seed Starter tray

Seed Sprouter Tray

Sullivan Dynatron Starter with Battery Box

Planter Seed trays - euro box norm 15x20cm

Seed Planter (Jiffy Pellet)

Seedling Transplant Tongs

Self-watering seed starter

Party Cup Plant Tray

Plant Tag

stackable seed tray 3x3

Propagation Cup Holder

Proton Seed Starter Tray