The Shelf Stack
Vertical indoor hydroponic system for continuous leafy green production.
Fits against a wall in a kitchen, garage, or spare room. Uses passive Kratky-method totes — no pumps, no plumbing, no electricity beyond grow lights and a timer. Produces enough lettuce, herbs, and greens to meaningfully supplement a family of four year-round. This is the rig the Window Farm prepares you for — same hydroponic principles, scaled up to where it actually replaces grocery store produce.
② The Manifest
The parts list. Cores are what you actually need; “if you prefer” opens cheaper, local, or heritage swaps — never budget fallbacks, just other good ways.
NSF-rated chrome or black wire shelving. Adjustable shelf height — set 18" between shelves to leave room for plants + lights. Same unit used in The Rack Farm.
if you prefer… (2)
No pump, no electricity for water. Roots draw down water level over the cycle, creating the air gap that oxygenates the roots. The simplest possible hydroponic method at this scale.
if you prefer… (2)
Black or dark-colored totes only — light penetration causes algae. Standard 10-gal totes measure roughly 24"×16"×12". One tote per growing shelf, with the top shelf reserved for seedling germination.
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2" for leafy greens and herbs (most uses). 3" for chard, kale, or pak choi. Drill matching holes in the tote lids; spacing 6" center-to-center for lettuce, 4" for herbs. About 9–12 sites per tote.
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pH-neutral, reusable (rinse and sterilize between grows), excellent root oxygenation. Fill net pot with hydroton around the seedling/cube.
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Mount under each shelf to illuminate the level below. Two lights per shelf gives even coverage across the 48" width. Same lights used in The Rack Farm.
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Plug all lights into a power strip, plug the strip into the timer. Set 14 hrs on / 10 hrs off. Lettuce can suffer from too much light (becomes bitter); 14 hrs is the sweet spot for leafy greens.
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Three bags. Cheapest cost per gallon of nutrient solution. Standard for serious home hydroponics. Critical: mix in order, dissolve completely between additions, never pre-mix the dry components or you'll get nutrient lockout. Full ratios in Sequence Step 04.
if you prefer… (2)
Drops are fine at this scale — fast, cheap, no calibration. Target pH 5.5–6.0 for lettuce. Most tap water needs 1–2 ml of pH Down per gallon to land in range.
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Measures the strength of your nutrient solution. Target 800–1200 ppm (0.8–1.2 mS/cm) for lettuce. As plants drink, EC drops — when it falls below 600, top off with fresh nutrient solution.
Most municipal tap water works fine after off-gassing chlorine. If your tap water is above pH 8.0 or has high mineral content, switch to filtered or RO. Fed from the Well domain (rainwater, well water, or filtered) — see Feeds.
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See Crop Timing Chart for variety recommendations. Start from seed in rockwool cubes or buy seedlings from a garden center for instant planting.
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③ The Sequence
④ Reference Tables
Crop Timing Chart
Days-to-harvest, spacing, and difficulty by variety — pick by what you'll actually eat
| Variety | Type | Days to harvest | Spacing | Difficulty | Notes |
|---|---|---|---|---|---|
| Buttercrunch / Bibb | Butterhead lettuce | 28–35 days | 6" centers | Easy | Forms a loose head. Soft, buttery texture. Beginner's gold standard. |
| Salanova / Salad Bowl | Loose-leaf lettuce | 25–35 days | 6" centers | Easy | Cut-and-come-again — harvest outer leaves, plant keeps growing. |
| Romaine / Cos | Romaine lettuce | 28–35 days | 6" centers | Easy | Crisp upright leaves. Slower to bolt in heat than other varieties. |
| Red Sails / Red Salad Bowl | Loose-leaf, colored | 30–35 days | 6" centers | Easy | Striking red coloration, mild flavor. Heat-tolerant. |
| Arugula | Spicy green | 21–30 days | 4" centers | Easy | Fast, peppery; harvest small for milder flavor or larger for spicy. |
| Spinach | Leafy green | 30–45 days | 4" centers | Moderate | Slower than lettuce. Bolts in heat above 75°F. Wants stable cool temps. |
| Kale (dwarf varieties) | Leafy green | 35–50 days | 8" centers | Moderate | Larger plant — only 4–6 per tote. Long-lived; harvest outer leaves for months. |
| Swiss Chard | Leafy green | 35–45 days | 8" centers | Moderate | Cut-and-come-again. Beautiful colored stems. |
| Pak Choi / Bok Choy | Asian green | 30–40 days | 6" centers | Easy | Fast, crisp, mild. Works well in stir-fries. |
| Basil | Herb | 30–45 days from seed; 14d from cutting | 4" centers | Easy | Continuous harvest by pinching tops. One plant produces for months. |
| Cilantro | Herb | 30–40 days | 4" centers | Moderate | Bolts quickly in heat. Use slow-bolt varieties or stagger every 2 weeks. |
| Parsley | Herb | 45–60 days | 4" centers | Easy | Slow to start but very long-lived. One planting can produce for 6+ months. |
| Mint | Herb | 14 days from cutting | 4" centers | Easy | Almost impossible to kill. Best from a grocery store cutting rooted in plain water. |
Nutrient Doses by Volume
Mix in order — Masterblend → Epsom → Calcium Nitrate. Never pre-mix the dry components.
| Volume | Masterblend 4-18-38 | Epsom Salt | Calcium Nitrate |
|---|---|---|---|
| 1 gallon | 2.4g (≈0.4 tsp) | 1.2g (≈0.2 tsp) | 2.4g (≈0.4 tsp) |
| 5 gallons | 12g | 6g | 12g |
| 10 gallons (tote) | 24g | 12g | 24g |
| Per dose ratio | 2 parts | 1 part | 2 parts |
Target Numbers
What to aim for — and what to do when you're outside the band
| Metric | Target | Action if out of range |
|---|---|---|
| pH | 5.5–6.0 | High → add pH Down 1 ml/gal at a time. Low → add pH Up sparingly (raises salts). |
| EC / TDS | 0.8–1.2 mS/cm (~800–1200 ppm) | Low → top off with fresh nutrient solution. High → dilute with plain water. |
| Water temp | 65–72°F | Above 75°F invites root rot. Move to cooler location, add ice bottles, or insulate tote. |
| Air temp | 65–75°F | Above 80°F causes bolting (premature flowering, bitter taste). |
| Light cycle | 14 hrs on / 10 hrs off | Too much → bitter taste. Too little → leggy growth. |
| Light distance | 6–12" above canopy | Too close → leaf burn. Too far → leggy stretching. |
Common Failure Modes
Symptom → cause → fix. Most failures collapse to one of five patterns.
| Symptom | Most likely cause | Fix |
|---|---|---|
| Roots brown, slimy, smelling of sulfur | Root rot from warm water (>75°F) or low oxygen | Drop water temp (ice bottles, move location), add air stone, replace solution. Trim brown roots; healthy white tips will regrow. |
| Green / brown algae coating the tote walls | Light reaching the nutrient solution | Wrap tote in foil, opaque tape, or paint flat black on the outside. Algae competes with roots for nutrients and oxygen. |
| Leggy, pale, stretching upward | Light too far above canopy or photoperiod too short | Lower light to 6–8" above canopy; verify timer is running 14 hrs on. LED panels appear bright to humans but are weak vs. plant demand. |
| Bitter / bolting (flowering early) | Air temp >80°F or photoperiod >16 hrs | Move to cooler location or shorten photoperiod to 14 hrs. Bolted plants don't reverse — harvest immediately, restart with fresh seeds. |
| Burnt leaf tips, white crust on roots | EC too high (over-fertilized) or pH drift | Dilute solution by 50% with fresh water; retest pH and EC. Burnt tips don't recover but new growth will be normal. |
| pH won't hold steady (drifts up daily) | Plant uptake of nitrate naturally raises pH | Normal at small scale — adjust 2–3× per week with pH Down. Drift slows as plants mature. Larger reservoirs drift slower. |
| Fungus gnats around the tote | Damp surface, organic media, overwatering at seedling stage | Top with 1" of perlite or coarse sand, let surface dry between waterings. Yellow sticky traps reduce adult population. |
| Plants healthy but yields low | Variety mismatch (slow grower) or under-fertilization | Check Crop Timing chart for expected days-to-harvest; verify EC is in target band. Consider variety swap to faster cultivars. |
Maintenance Rhythm
Daily / weekly / monthly checklist — under 5 minutes a day once dialed in
| Frequency | Action | Time |
|---|---|---|
| Daily | Visual check: water level, root color, leaf health, no obvious failures | 1 min |
| Daily | Top off reservoir with plain water if level dropped (evaporation only — don't add nutrients) | 1 min |
| 2–3× / wk | Test pH, adjust to 5.5–6.0 | 3 min |
| Weekly | Test EC / TDS, top off with fresh nutrient solution if low | 5 min |
| Weekly | Trim outer leaves on cut-and-come-again crops; harvest mature plants | 10 min |
| Monthly | Drain reservoir, scrub tote with diluted bleach (1 tbsp / gal), rinse 3×, refill | 30 min |
| Monthly | Inspect light fixtures, clean reflectors / lens, verify timer | 5 min |
| Quarterly | Replace seed stock for varieties showing reduced germination | 15 min |
Scaling — When to Graduate
Signs you've outgrown the Shelf Stack and the natural next-step rigs
| Signal you're ready to expand | Where to go next |
|---|---|
| You want fruiting crops (tomatoes, peppers, strawberries) | Porch Garden (wicking bed) or Walipini (year-round). Kratky doesn't suit fruiting crops — they need active aeration and more nutrients than passive Kratky delivers. |
| You want microgreens or sprouts at meal scale | Rack Farm — purpose-built for fast-cycle short-tray crops alongside the Shelf Stack. |
| You want fish protein in addition to greens | Living Shelf — adds aquaponics. Same shelving family, plus a fish tank below. |
| You're outgrowing 4 totes and want continuous bulk greens | Multi-shelf Shelf Stack scale-up: add a second 4-tote shelf, stagger planting weeks. Still passive Kratky. |
| Your kitchen counter is full and you want a basement / garage rig | Move the Shelf Stack to dedicated space. The rig pattern stays identical, the location doesn't. |
| You want automation, app monitoring, or larger volumes | Active hydroponic system (DWC, NFT, ebb-flow) — outside the Kratky pattern. New rig category. |
Electrical / Water Safety
Non-negotiable rules — water and electricity in close proximity demand discipline
| Rule | Why |
|---|---|
| Plug all rig devices into a GFCI outlet | GFCI cuts power within 30ms of detecting a ground fault — the difference between a startle and a stop-the-heart event. Bathroom-grade GFCI is fine; ensure it's actually a GFCI, not a regular outlet. |
| Use a drip loop on every cord entering the shelving | Form a U-shape so any water running down the cord drips off at the low point instead of into the outlet or device. |
| Position power strips above the highest tote, never below | If a tote leaks or overflows, gravity wins. Power strips above water; cords routed downward to devices. |
| No open splices, no daisy-chained extension cords | One clean cord per device to a properly-rated outlet. Daisy chains are how house fires start. |
| Inspect cords monthly for nicks, frays, or melted insulation | Heat from grow lights + humidity from the rig accelerates insulation breakdown. Replace any cord showing wear. |
| LED drivers and pumps should be rated for damp environments | Look for IP44 or higher on labels. Indoor-only ratings (IP20) fail predictably in a high-humidity grow environment. |
| If you see water near a powered device, kill the breaker first | Don't unplug a wet device. Kill the circuit at the breaker, then handle the device safely once it's de-energized. |
⑤ The Echo
Why passive hydroponics works at all — the elegant biology of the Kratky air gap. Roots need oxygen as much as they need water and nutrients; in a soil garden, oxygen comes from air pockets between particles, but in hydroponics you have to engineer it deliberately. Kratky solves this by letting the plant drink down the water level over the cycle, naturally creating an aerial root zone above and a nutrient-soaked root zone below. The genius of the system is that it self-regulates — the air gap grows automatically as the plant grows. No pump, no airstone, no electricity for water movement, just the plant doing its own work. Why this works for leafy greens (low oxygen demand, fast cycle, single nutrient charge) but doesn't work as well for fruiting plants — tomatoes and peppers want continuous nutrient replenishment and more dissolved oxygen, which is why those rigs use NFT or Dutch buckets. When to graduate from Kratky to active systems: scale, fruiting plants, automation, or commercial production. Why for a household feeding system, Kratky is almost always the right answer.
The Shelf Stack is not just a hydroponic rig — it's the first link in the household food chain. The harvest from this rig flows directly into The Living Pantry as fresh greens, into daily salads and meals, and creates a feedback loop between what you grow and what you eat. Why the harvest-to-kitchen pipeline matters: lettuce loses nutrients within hours of harvest. Store-bought 'fresh' greens are often 7–14 days old by the time you eat them. Greens cut 30 seconds before they hit the salad bowl are nutritionally a different food. The psychological shift that happens when you stop adding 'lettuce' to the grocery list — your kitchen behavior changes, your cooking gets braver, your meals get more vegetable-dense because the supply is endless and free. How staggered planting (one tote planted every 1–2 weeks) creates a continuous flow that mirrors the FIFO discipline of The Living Pantry. Why this rig pairs naturally with The Rack Farm — daily microgreens for garnish, weekly heads of lettuce for the main course. Two rigs, complementary cycles, fresh food every day. The Shelf Stack is where the household food chain starts becoming sovereign.
⑥ Feeds
How this rig connects to the rest of the Ark.
- → material The Gut Spent nutrient water → biodigester input or outdoor soil irrigation
- → material The Worm Bank Plant trimmings and root mass → vermicomposting feedstock
- ← material The Gut Digestate (filtered, diluted) → supplemental hydroponic nutrients
- ← material The Worm Bank Vermicast tea → foliar spray or root drench
- ← material The Smith Fabricated trellises, raised bed hardware, irrigation fittings
- ← energy The Sun Bank Solar → powers hydroponic pumps and grow lights
- ← information The Sentry Water temp, pH, humidity telemetry from hydro rig
- ← information The Vault Offline reference material for Grow Sequences
- → material The Living Pantry Surplus leafy greens from hydroponic harvest dehydrated or frozen into pantry preservation pipeline
- ← information The Window Farm The Window Farm is the gateway rig for The Shelf Stack — Kratky method, nutrient mixing, pH management, and light assessment all transfer directly when a builder graduates from 6 jars on a window to a full vertical hydroponic rack
- ← information The Rack Farm Graduation path — same shelving, same lights, same stagger concept; everything learned about light, timing, and rotation here transfers directly when scaling up to full-size leafy greens
- ← material The Sky Well Rainwater is the ideal source — naturally low pH (5.5–6.5 in clean rain), chlorine-free, and free; a 10-gal tote uses ~8 gal per cycle, so a Sky Well easily supports a 4-tote rig
- → information The Rack Farm Parallel and complementary — Rack Farm produces microgreens daily, Shelf Stack produces full-size greens weekly; both share shelving, lights, and growing-medium suppliers, so build them together
- ← material The Seed Bank Saved seed stocks the Shelf Stack crop plan.
⑧ Go Deeper
ManyArks endorses no single source — these are starting points that fit the Ark philosophy. In a Vault bundle, these external links require the clearnet.
Concept
What is this and why does it work?
Build
How do I build one?
Indoor shelf hydroponic build (Kratky)
Net pot lid drilling template for storage totes
Troubleshoot
Mine isn't working
Adapt
How do I modify this for my situation?
grow/shelf-stack
Offline? Same path on any Ark Mirror.