HydroPlant Cap
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HydroPlant Cap — AlphaHelix.io A 3D-printed twist-off cap that turns any standard glass jar into a passive hydroponic pl
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Model information
- Source
- Printables
- Category
- Outdoor & Garden
- License
- Creative Commons — Attribution — Noncommercial — NoDerivatives
HydroPlant Cap — A 3D-printed twist-off cap that turns any standard glass jar into a passive hydroponic planter — no soil, no pump, no electricity
Follow alphahelix.io on instagram for more models and concepts.
Sizes TO number = outer neck diameter in mm, matched to standard twist-off canning jars:
TO 66 — Ø66mm, 0.37L jars
TO 82 — Ø82mm, 0.7L jars
TO 89 — Ø89mm, 1.7L jars
Custom: TO 53–TO 100 range, plus Mason wide-mouth 86mm, on request
Anatomy (TO82 variant shown, PETG · Ø86mm overall / 56mm tall / Ø46mm bottom opening)
Knurled rim — grip with wet hands
Twist-off thread (TO82) — fits the jar neck
Rockwool basket — holds the seed/cutting
Side windows — air in, roots out
Bottom opening — roots reach the water
How it works — 4 steps, no pump Soak rockwool + plant → fill jar to just below the basket, wool wicks it up → as the plant drinks, water level drops and an air gap forms so roots breathe → top up every few weeks, done.
What grows in it
Herbs: basil & mint fastest (first cut 3–4 weeks), plus chives, parsley, coriander, oregano, thyme, lemon balm
Leafy greens: leaf lettuce, arugula, spinach, pak choi, watercress
Houseplant cuttings: pothos, monstera, philodendron, tradescantia, spider plant (root in plain water first, then switch to nutrients)
Won't work: carrots, potatoes, tomatoes — need too much room/nutrients
Scaling from the 86mm reference
Scale % = (target Ø ÷ 86) × 100
Target | Diameter | Scale vs. 86mm | Resize |
|---|---|---|---|
TO 53 | 53 mm | 61.6% | shrink 38.4% |
TO 66 | 66 mm | 76.7% | shrink 23.3% |
TO 82 | 82 mm | 95.3% | shrink 4.7% |
Mason wide-mouth | 86 mm | 100% | reference, no change |
TO 89 | 89 mm | 103.5% | enlarge 3.5% |
TO 100 | 100 mm | 116.3% | enlarge 16.3% |
Note TO89 and TO100 are actually bigger than the 86mm reference, so those two are an enlarge, not a shrink. Any in-between size (TO70, TO75...) follows the same ratio.
One heads-up for production: this is uniform scaling of the whole model, so the 56mm height, 46mm bottom opening, and wall thickness all shrink/grow by the same %. Twist-off thread profiles aren't always perfectly linear across sizes in reality, so it's worth test-printing the thread fit at each scale before running PETG production batches — especially at the extremes (TO53, TO100).
Design note
The current design doesn't cut a true mating thread on the inside — it's a simplified twist/friction fit rather than a precise matching helix. This keeps the print geometry simple and avoids over-engineering it, though it does mean the fit is a bit looser on some bottle variants (less exact tolerance across different jar necks). The trade-off is intentional: easier handling — the cap twists on and off without needing exact thread alignment. Future iterations are planned to refine this further.