Stop top-watering your seedlings — a fully 3D printed bottom watering reservoir designed to feed your LGP grow cells from below, with a built-in float level indicator so you always know when it's time to refill.

The LGP Self-Watering Tray is a passive bottom watering reservoir that sits inside the Logical Grow Platform main body and holds any combination of LGP HalfTrays or ThirdTrays above a shallow water reservoir. Your grow cells wick moisture upward from below through their built-in 2-stage wicking systems, keeping the soil consistently moist from the roots up. It can also be used completely standalone on any surface, independent of the LGP main platform.

A word on "self-watering" — this term is standard in the growing world and describes any system where plants draw water upward from a reservoir below rather than being watered from the top. It does not mean automated or hands-free. You still fill the reservoir, check the level, and refill when needed. What it does mean is that your plants get consistent bottom moisture, top-watering disturbance is eliminated, and the risk of overwatering from the top is greatly reduced. Think of it as a smarter way to water, not a set-and-forget system.

In practice, based on my own growing experience, most configurations will need a refill every one to two days depending on plant size, ambient conditions, and which tray combination you're using. The reservoir capacity varies significantly by configuration since the grow cells sitting inside the tray displace a portion of the water volume. Checking daily and allowing the reservoir to cycle between wet and dry before refilling is good growing practice and helps build stronger root systems.

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Growing Guide I've documented what I've learned while designing and using the Logical Grow Platform in a growing guide series on LogicalPlanet.com, covering everything from seeds through harvest. https://www.logicalplanet.com/collections/lgp/

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How It Works

The Self-Watering Tray is built around four printed components.

Tray — The main reservoir body. Sits inside the LGP main platform or on any flat surface. Holds LGP HalfTrays and ThirdTrays above a shallow water reservoir.

Float Housing — Mounted inside the tray, the float housing contains the level indicator mechanism. The float rises and falls linearly with the water level, rotating the external indicator arm to show current reservoir status.

Fill Funnel — A printed funnel that clips to the end of the tray for easy, controlled filling without disturbing your grow cells or splashing soil.

Float — A two-part printed float with a buoyant hollow side and a weighted counterweight side. The balance between the two drives the indicator arm. Print settings for each side differ — see Printing Notes below.

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Filling & Level Indicator

Before reading the level indicator, always flick the indicator arm gently with your finger first. The float can stick slightly as water evaporates and the indicator may not reflect the true water level without this nudge. Once flicked, the arm will settle to the correct position.

To fill, pour water slowly through the fill funnel and watch the indicator arm rise. Stop filling when the indicator reaches the full mark. There is no overflow protection — if you fill past the full mark the water will simply spill out of the tray, so watch the indicator carefully as you fill.

For best visibility, use a permanent marker to colour the indicating surfaces on the float arm as shown in the instructions. This makes the indicator much easier to read at a glance.

Refill when the indicator shows low or when you notice the soil beginning to dry. In my experience, most setups need a refill every one to two days. Allowing the reservoir to run dry between refills and then refilling to full is good growing practice — the wet/dry cycle encourages roots to grow downward in search of moisture, building stronger, more resilient plants.

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Key Features

• Passive bottom watering reservoir for the full LGP ecosystem
• Compatible with all LGP HalfTray and ThirdTray combinations
• Built-in float level indicator — no guessing when to refill
• Fill funnel for controlled, splash-free filling
• Fits inside the LGP main platform body
• Usable standalone on any flat surface
• No hardware required — fully 3D printed
• 100% printed, no supports required

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Perfect For

• Consistent bottom moisture for seedlings and herbs
• Reducing top-watering disturbance during germination
• Integration with the full LGP system
• Standalone bottom watering on any surface
• Growers who want more control and visibility over their watering

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Printing Notes

This design holds water, so print settings matter more than usual. An increased flow ratio is strongly recommended for better waterproofing.

• Prints support-free in provided orientations
• PLA, PETG, or ASA recommended (see notes)
• 0.4mm nozzle, 0.2mm layer height, 4 walls, Arachne wall generator
• 40% infill for all parts except the float counterweight
• Float counterweight: 70% infill or higher — increase if the float is not responding to water level changes
• Float buoyant side: prints hollow regardless of slicer settings — use increased flow ratio for waterproofing
• Flow ratio: 1.04 (range 1.03–1.05 depending on your printer) — this significantly improves water resistance
• Brim/Raft: No
• Support: None required

Notes: PETG is a good choice for indoor water contact applications. ASA for long-term or outdoor use. PLA is adequate but less ideal for prolonged water exposure. The float buoyant side must remain hollow to function — do not override this with solid infill settings.

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Print with Confidence I design and test my models carefully, but if you run into what appears to be a genuine design issue — a fit problem, a tolerance that doesn't work, or something that just doesn't behave the way the instructions suggest — let me know and I'll fix it. My goal is that every design I publish works as described. Email me at logicalplanet3d@gmail.com with details and I'll sort it out.

Note: I'm not able to account for every printer and material combination, so I recommend reviewing the print settings carefully before starting. Issues arising from incorrect settings or materials are outside the scope of this, but I'm still happy to help troubleshoot.

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An Evolving System — Your Feedback Matters I've been growing in the LGP system for several months now, and that real-world experience has shaped almost every design decision in this release. It's been invaluable — and it's also shown me that no amount of bench testing replaces actually growing plants in a system over time.

I consider the LGP an evolving platform, not a finished product. If something works better a different way, or you discover something I haven't thought of, I genuinely want to hear about it. Your growing experience is part of what makes this system better for everyone. Reach out on Discord or email me at logicalplanet3d@gmail.com.

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Related Links Logical Grow Platform (LGP) — Main Platform https://than.gs/m/1511734

LGP 2×3 Cells XL HalfTray https://than.gs/m/1540074

LGP Single Cell HalfTray https://than.gs/m/1540075

LGP Single Cell ThirdTray https://than.gs/m/1540077

Deep Cell Plug Tray – 3×5 Modular Seed Starter System https://than.gs/m/1511704

Deep Cell Plug Tray – 2×5 Modular Seed Starter System https://than.gs/m/1511705

Deep Cell Plug Tray – 3×2 Modular Seed Starter System https://than.gs/m/1511706

Join the LogicalPlanet Discord https://linktr.ee/logicalplanet

Visit my blog for more details and other designs https://www.logicalplanet.com/

Revisions and Updates I occasionally update and revise my designs. When I do, I'll document the changes here. Check back periodically for the latest revision notes or if you're experiencing any issues with a model. Please email me at logicalplanet3d@gmail.com if you would like me to make a revision or have comments about this design.

2026-04-17: Initial release.