Kratky Method Hydroponics — The No-Pump Canadian Setup
The simplest hydroponic method in existence: no pumps, no electricity to the reservoir, no nutrient changes. A mason jar of lettuce, fresh in 30 days, for under thirty dollars. Step-by-step, container sizes, and what to do when things drift.
The short version: Kratky is passive hydroponics — a sealed container of nutrient solution, a plant in a net pot at the top with roots reaching down. As the plant drinks, the water level drops, exposing roots to air. No pumps, no power, no nutrient changes. Works because leafy greens and herbs finish their lifecycle before the reservoir runs dry. Cheapest entry to hydroponics in Canada (~$30), set-and-forget, and impossible to screw up if you keep an air gap between roots and water.
Kratky is the hydroponics method to start with if you have never grown without soil. Developed by Dr. Bernard Kratky at the University of Hawaii, it strips away every active component — no pumps, no airstones, no timers, no nutrient swaps — and still produces a head of lettuce in 30 days. For a Canadian apartment with a south-facing window or a small grow light, it is the most reliable way to eat your own salad in February.
How Kratky Actually Works
The trick is the air gap. At the start, the nutrient solution touches the bottom of the net pot — roots reach down and drink. As the plant grows, it drinks the solution down. The water level falls. Roots that started underwater are now exposed to air, which is exactly what root tissue wants for oxygen uptake. The deeper, younger roots stay below the water line and keep feeding the plant; the upper roots, now in air, do most of the breathing.
By the time the reservoir is mostly empty, the plant is mature and ready to harvest. The system has run itself with no inputs after the initial fill. That is the whole design.
What breaks it: not leaving an air gap. If you keep topping up the reservoir to the rim, the entire root system stays underwater, the plant suffocates, and the roots rot. The Kratky rule is simple: always keep at least half the root mass in air.
What You Need — Canadian Sources
| Item | Cost (CAD) | Where |
|---|---|---|
| Opaque container (4–6 L for lettuce, 10–20 L for tomatoes) | $0–15 | Reuse a yogurt tub or buy a black tote bin at Canadian Tire |
| Net pot (5 cm for greens, 7.5 cm for fruiting) | $1–3 | Amazon.ca, hydro shops |
| Growing medium (clay pebbles or rockwool cubes) | $8–15 / bag | One bag lasts dozens of plants |
| Two-part hydroponic nutrient (General Hydroponics Flora, MasterBlend, etc.) | $25–45 | Lasts a full year for a small setup |
| pH test drops or meter | $10–25 | Drops fine for beginners; meter for serious use |
| pH up/down adjuster | $15–25 | Small bottles last years |
| Optional: small LED grow light | $30–90 | 15–40W clip lights run for ~15¢/day |
Step-by-Step — Single-Jar Kratky Lettuce
1. Start the seedling
Soak a rockwool cube in pH 5.8 water, drop a lettuce seed in the top hole, and keep warm and lit until two true leaves emerge (10–14 days). Skip this step by buying a lettuce seedling from a garden centre and gently rinsing the soil from its roots.
2. Mix the nutrient solution
Follow your nutrient label for "leafy greens" or "seedling" strength. For General Hydroponics Flora trio that is roughly 2 mL of each per litre. Mix in a clean jug of room-temperature water, then check pH and adjust to 5.8–6.2 with pH down/up drops.
3. Prep the container
Cut a hole in the container lid sized for the net pot (most net pots have a lip that holds them in a roughly 5 cm hole). Fill the container with nutrient solution until the level just touches the bottom of where the net pot will sit — this is critical: too low and the roots can't reach; too high and you lose the air gap from day one.
4. Plant in the net pot
Drop the seedling (rockwool cube and all, or roots-rinsed seedling) into the net pot, packing clay pebbles around it for support. Sit the net pot in the container hole. The bottom of the net pot should just touch the nutrient solution. Roots will reach down into the water within days.
5. Place under light, leave it alone
South-facing windowsill (winter sun helps) or a 14–16 hour grow-light schedule. Keep at 18–22°C. Do not top up. Do not stir. Lettuce harvests in roughly 30 days from this point; the reservoir empties as the plant grows, exactly as designed. Harvest the whole head when it looks ready, or pick outer leaves as needed.
Container Sizing by Crop
| Crop | Container size per plant | Time to harvest |
|---|---|---|
| Lettuce (Buttercrunch, Romaine) | 3–4 L | 30–45 days |
| Kale, bok choy, arugula | 3–5 L | 35–50 days |
| Basil, parsley, cilantro | 2–3 L | 40–60 days, then pick-and-come-again |
| Cherry tomato (small varieties) | 15–20 L | 90–110 days; top-ups needed |
| Strawberry (everbearing) | 5–8 L | Continuous fruiting; top-ups needed |
| Pepper (small varieties) | 15–20 L | 100–120 days; top-ups needed |
Kratky Troubleshooting
Green / algae-coloured water
Light is reaching the reservoir. Switch to an opaque container, wrap a clear jar in foil, or paint glass containers black on the outside. Algae alone isn't dangerous but it competes with the plant for nutrients and can spawn root rot.
Slimy brown roots, plant wilting
Root rot from no air gap (you topped up too high) or warm reservoir water (over 24°C). Pull the plant, rinse roots, trim slimy sections, refill the reservoir with fresh cooler nutrient solution to the proper level, and ensure the upper half of the root mass sits in air. Full root rot fix →
Yellow lower leaves
Usually nitrogen deficiency from the reservoir running low on nutrients, or pH drift out of range. Check pH (target 5.8–6.2) and EC. A partial reservoir refresh fixes most cases.
Roots dangling without reaching water
Reservoir started too low. The bottom of the net pot should touch the solution at start; if there is a gap, roots can't bridge it on a small plant. Top up to just below the net pot lip and let the roots take it from there.
Plant bolting (going to seed)
Reservoir too warm, too much light, or summer-bolting variety. Move to a cooler spot, reduce light hours to 14, and pick bolt-resistant lettuce varieties (Buttercrunch, Adriana, Salanova).
Frequently Asked Questions
Is the Kratky method really maintenance-free?
For lettuce and most leafy greens, yes — once set up, you do nothing until harvest. For longer-running crops (tomatoes, peppers, strawberries) you do top up with pH-adjusted plain water occasionally, but no nutrient changes, no pumping, no aerating. It is the lowest-effort hydroponic method by a wide margin.
Can I run multiple plants in one Kratky bin?
Yes — this is the most efficient setup once you're past the single-jar starter. A 20-litre black tote bin with 6 net pot holes in the lid grows 6 lettuces simultaneously with no extra effort. Space the holes 15–20 cm apart. Each plant gets roughly 3 L of reservoir, which is right for greens.
Why don't the roots rot if they're sitting in stagnant water?
Because most of the root mass isn't underwater for long. The roots that grow first reach the solution and stay there briefly; as the plant grows, the water drops, and those roots find themselves in air, which they prefer. Plants are smart about putting different parts of the root system to different jobs: some absorb water, others absorb air. The Kratky design exploits that. Rot only happens if you defeat it by topping up to the brim.
DWC vs Kratky — which should I start with?
Start with Kratky for the first 1–2 successful harvests, then move to DWC if you want faster growth and bigger plants. Kratky is cheaper, simpler, and forgiving of beginner mistakes. DWC (deep water culture) adds an air pump to oxygenate the reservoir, which produces faster growth and supports larger plants — but the pump fails are now part of the failure mode. Most experienced Canadian indoor growers run Kratky for greens and herbs and DWC for fruiting crops. Full system comparison →
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