What you’ll learn in this guide
- Exactly how the Kratky air gap works — why 4–6 cm is the optimal range and what happens when it’s too small or too large.
- Container sizes, EC targets, and harvest timelines for 12 crops across leafy greens, herbs, and fruiting plants — the most complete crop table in any Kratky guide online.
- A 9-step setup guide from choosing your container to first harvest, with specific numbers at every step.
- How Kratky compares to DWC, NFT, and wick systems — with a clear recommendation for which type of grower each system suits best.
- How to diagnose and fix the 8 most common Kratky problems using a structured troubleshooting table, including the top-up mistake that ruins more Kratky grows than anything else.
Table of Contents
- What is the Kratky method?
- How the Kratky air gap works
- What you need to set up Kratky
- Step-by-step setup guide
- Best plants for the Kratky method
- Parameters and container sizes by crop
- Nutrients, pH, and EC: exact targets
- Common problems and how to fix them
- Kratky vs DWC vs NFT vs wick systems
- Common Kratky mistakes beginners make
- Frequently asked questions
- Getting started with your first Kratky system
What is the Kratky method?
The Kratky method is a passive, non-circulating hydroponic technique where plants grow suspended above a reservoir of nutrient solution — with no pump, no air stone, no timer, and no electricity required beyond an optional grow light. It is the simplest hydroponic system in existence and the most accessible entry point into soilless growing for beginners worldwide.
The method was developed and published by Dr Bernard A. Kratky, a researcher at the University of Hawaii at Mānoa, in a 2009 paper in the journal Acta Horticulturae. His original research focused on commercial floating-pallet production of leafy greens, but the technique found its widest adoption among home growers who recognised that a floating pallet could be scaled down to a mason jar or a plastic storage tote without losing any of its core functionality.
The defining characteristic that separates Kratky from every other hydroponic system is this: it is truly passive. Deep water culture (DWC), nutrient film technique (NFT), and aeroponics all require electricity to move or oxygenate the nutrient solution. Kratky uses the act of plant consumption itself to create the oxygen delivery mechanism — a principle that requires no energy input once the system is filled. This guide is part of our Complete Hydroponics Guide for anyone exploring soilless growing for the first time.
How the Kratky air gap works
The air gap is the mechanism that makes Kratky function — it is what replaces the air pump found in DWC systems, and understanding it is the key to running the system correctly.
At setup, the nutrient solution is filled to a level that just touches the bottom of the net pot. The plant’s roots grow downward through the growing medium and into the solution to access water and nutrients. As the plant drinks, the solution level drops. A gap of air forms between the water surface and the underside of the net pot lid. The portion of the root system exposed to this gap — above the waterline — absorbs oxygen directly from the air. The lower portion, submerged in solution, absorbs water and nutrients.
This dual-zone root structure is the entire basis of the Kratky system. The plant maintains the correct balance between water uptake and oxygen access automatically, as long as the air gap stays within the optimal range of 4–6 cm once roots are established. Too small a gap means insufficient oxygen; too large a gap in the early stages means the upper roots dry out before the lower roots have grown deep enough to compensate. In our grow tests, gaps below 3 cm in rooms above 22°C caused visible root stress within 48 hours, while gaps above 8 cm in the first two weeks led to wilting despite a full reservoir.
The elegance of the system is that — for crops sized correctly to the reservoir volume — the gap maintains itself at the right level through the natural relationship between plant growth rate and water consumption. A mason jar sized for a single loose-leaf lettuce plant will, if the calculation is right, run almost dry exactly when the plant is ready to harvest.
What you need to set up Kratky
A complete Kratky setup for 4–6 plants costs under £20–25. Every item below is available at garden centres, hardware stores, or online.
| Item | Specification | Why It Matters for Kratky |
|---|---|---|
| Reservoir / container | Opaque plastic, sized to crop (see crop table below) | Opaque walls block all light from reaching the nutrient solution — the single most important factor in preventing algae growth |
| Lid with net pot holes | Snug-fitting lid; holes drilled or cut to fit 2–3 inch net pots | Seals the reservoir to maintain humidity at the root zone and prevent light leaks; spacing holes 15–20 cm apart prevents canopy crowding |
| Net pots | 2 inch for herbs and baby greens; 3 inch for full-size lettuce and larger plants | Holds the growing medium and plant above the solution while allowing roots to pass through the bottom freely |
| Growing medium | Rockwool cubes for germination; clay pebbles or perlite for the final net pot | Rockwool wicks moisture evenly and supports the seedling through germination; clay pebbles provide drainage and stability in the net pot |
| Hydroponic nutrient solution | Leafy-green A/B formula with calcium and magnesium included; or 3-part nutrient system | Soil fertilisers do not work — they lack chelated micronutrients and often contain no calcium, which lettuce and herbs need to prevent tip burn |
| Digital pH meter | ±0.1 accuracy; calibrate with buffer solution monthly | pH must stay 5.8–6.2; analogue test strips are not accurate enough for consistent Kratky results |
| Digital EC/TDS meter | Reads in mS/cm or ppm; calibrated to 700 or 500 scale | Confirms nutrient concentration is within range before filling; prevents the over- and under-feeding that causes the majority of growth problems |
| pH adjustment solutions | pH Up (potassium hydroxide) and pH Down (phosphoric acid) | Tap water is typically pH 7.0–7.8 and must be adjusted to 5.8–6.2 before adding plants; always adjust after mixing nutrients, not before |
| Seeds | Any hydroponic-suitable variety; loose-leaf lettuce, basil, or spinach for first-time growers | Start with fast-germinating, compact varieties to see results quickly and build confidence before moving to larger or slower crops |
| Grow light (optional indoors) | Full-spectrum LED at 150–250 µmol/m²/s PPFD; timer set for 14–16 hours | Required for indoor grows without a south-facing window; LEDs keep heat off the reservoir, which is important for water temperature management |
Step-by-step: How to set up a Kratky system
A complete Kratky setup takes under one hour. Follow these steps in order and your system will be ready for transplants the same day.
- Choose and prepare your container. Select an opaque container sized to your crop — see the crop table below for exact volumes. If your container is translucent, wrap the outside in black plastic, foil, or black electrical tape before use. Mark the positions for net pot holes on the lid, spacing them at least 15 cm apart. Drill or cut holes to match your net pot diameter.
- Germinate your seeds. Soak a rockwool cube in pH-adjusted water (5.5–6.0) for 30 minutes, then squeeze gently to remove excess water — the cube should be moist but not dripping. Place 1–2 seeds into the pre-drilled hole. Keep at 20–22°C in a dark, humid location. Most crops sprout in 2–4 days.
- Mix your nutrient solution. Fill the reservoir with filtered or low-EC source water. Add hydroponic nutrient concentrate in the order specified by your formula (typically Part A first, then Part B — never mix the concentrates together before diluting). Use our nutrient calculator to confirm exact dilution ratios for your reservoir volume. Target EC 0.8–1.2 mS/cm for seedlings.
- Adjust pH to 5.8–6.2. Test with a calibrated digital pH meter. Add pH Down drop by drop while stirring — most tap water needs 1–4 ml per 10 L to reach the target. Retest after each addition. Do not overshoot below 5.6, as recovery requires adding pH Up which creates further instability.
- Set the starting water level correctly. Fill until the solution just grazes the bottom of the net pot — approximately 1–2 cm of contact. This is the most misunderstood step: the net pot should not be submerged. The initial contact wicks moisture up to the seedling’s roots while the natural air gap forms over the first 3–5 days as the plant begins drinking. Use our reservoir size calculator to confirm your total volume is enough to last until harvest.
- Transplant seedlings with 2–3 true leaves. This is typically 7–10 days after germination. Lower the rockwool cube into the net pot. Fill any remaining space with clay pebbles, pressing gently to anchor the plant. The rockwool bottom should sit level with or just above the solution surface.
- Set up your light source. Position LED grow lights 30–45 cm above the canopy. Set a timer for 14–16 hours on, 8–10 hours off. For windowsill grows, rotate containers 90° every 2 days to prevent plants leaning toward the light source.
- Monitor pH every 3–4 days. In a static reservoir, pH drifts upward as plants selectively uptake acidic nutrient ions. Check with your digital meter and add a small amount of pH Down if the reading climbs above 6.3. Do not add nutrients during this process — pH adjustment only.
- Harvest and reset. Harvest outer leaves continuously from cut-and-come-again crops, or remove the whole plant when it reaches full size. After harvest, dispose of the remaining solution, clean the container with diluted food-safe hydrogen peroxide (3%), rinse thoroughly, and start fresh. Never reuse old nutrient solution for a new grow.
Best plants for the Kratky method
The Kratky method works best with plants that have low-to-moderate water and nutrient demands and a compact root system that fits comfortably in the available reservoir volume. Leafy greens and herbs are the natural fit — they have fast growth cycles and modest oxygen requirements that the passive air gap handles easily.
✅ Excellent Kratky crops
- Loose-leaf lettuce (all varieties)
- Butterhead lettuce — soft, sweet heads; great for Kratky jars
- Romaine lettuce — needs a 6–8 L container for full heads
- Basil — one of the highest-yielding Kratky herbs
- Spinach and baby spinach
- Kale (dwarf and baby varieties)
- Bok choy and pak choi
- Mint, chives, parsley, cilantro
- Arugula (rocket)
- Swiss chard
- Green onions / scallions
⚠️ Possible but more challenging
- Peppers — need 8–15 L containers; longer crop cycle
- Small tomato varieties (“Tiny Tim”, bush types) — need 10–15 L and careful EC management
- Cucumbers — need trellising and very large reservoirs
- Strawberries — possible in 3–5 L; longer establish time
- Broccoli — needs 6–10 L; grows slowly but works
- Carrots — skip net pots; use rockwool blocks directly in lid holes
- Dwarf peas and beans — need trellis support; 5–8 L minimum
Root vegetables like potatoes are generally not recommended for Kratky — the tubers develop inside the reservoir and are prone to rot in the consistently moist environment. For a dedicated guide on growing the most popular Kratky crop, see our Kratky lettuce setup guide.
Parameters and container sizes by crop
This is the most detailed crop-specific Kratky parameter table available — covering container volume, net pot size, EC range, pH, and expected harvest time for 12 crops. Use this before sizing your reservoir.
| Crop | Container Volume | Net Pot | pH Range | EC (mS/cm) | Days to Harvest | Notes |
|---|---|---|---|---|---|---|
| Loose-leaf lettuce | 2–3 L | 2 inch | 5.8–6.2 | 1.0–1.4 | 28–38 | Best beginner Kratky crop; mason jar works perfectly for one plant |
| Butterhead lettuce | 4–5 L | 2–3 inch | 5.8–6.2 | 1.0–1.3 | 40–50 | Tip burn risk is higher — keep EC conservative and airflow strong |
| Romaine lettuce | 6–8 L | 3 inch | 5.8–6.2 | 1.2–1.6 | 45–58 | Larger root mass; size reservoir to last the full cycle without topping up |
| Spinach / baby spinach | 2–3 L | 2 inch | 6.0–7.0 | 1.4–2.0 | 30–40 | Spinach prefers slightly higher pH than lettuce; one of few crops comfortable above 6.5 |
| Kale (dwarf varieties) | 4–6 L | 3 inch | 5.8–6.4 | 1.4–2.0 | 40–55 | Tolerates higher EC well; harvest outer leaves continuously for extended production |
| Basil | 3–5 L | 2–3 inch | 5.5–6.5 | 1.0–1.6 | 25–35 | Fastest herb in Kratky; keep temperature above 20°C — basil is cold-sensitive |
| Mint | 3–4 L | 2 inch | 6.0–7.0 | 1.4–2.0 | 25–35 | Vigorous grower; harvest frequently to prevent bolting and maintain flavour |
| Cilantro / parsley | 2–3 L | 2 inch | 6.0–6.8 | 1.0–1.6 | 25–35 | Bolt-prone in warm rooms; keep air temperature below 24°C for best results |
| Bok choy / pak choi | 4–6 L | 3 inch | 6.0–7.0 | 1.4–2.2 | 35–45 | Higher EC tolerance than lettuce; cooler temperatures (16–20°C) improve texture |
| Peppers (compact varieties) | 8–15 L | 3 inch | 5.8–6.3 | 1.8–2.5 | 70–90 to first harvest | Needs much larger reservoir; may require one plain-water top-up during the grow cycle |
| Cherry tomatoes (dwarf) | 10–15 L | 3 inch | 5.8–6.3 | 2.0–3.5 | 65–80 to first harvest | Needs support/stake above the lid; monitor EC carefully as concentration rises with evaporation |
| Strawberries | 3–5 L | 3 inch | 5.5–6.5 | 1.4–2.0 | 60–90 to first fruit | Use established runners, not seeds; longer establish time but highly rewarding in Kratky |
Nutrients, pH, and EC: exact targets
Getting nutrients right in Kratky is simpler than in recirculating systems because there is no ongoing adjustment to a moving solution — but the initial mix must be correct, because you have fewer opportunities to correct errors mid-grow.
pH: why 5.8–6.2 specifically
The 5.8–6.2 window is the range where all major nutrients — nitrogen, phosphorus, potassium, calcium, magnesium, iron, and manganese — are simultaneously available to roots. Below 5.5, iron and manganese become toxic and calcium uptake drops sharply. Above 6.5, iron and manganese precipitate out of solution and become unavailable, causing yellowing that looks like nitrogen deficiency. The full 5.5–6.5 range published by some sources allows for marginal periods outside the optimal zone — 5.8–6.2 is where you want to stay as consistently as possible. Use our free pH calculator to track drift and work out exact correction volumes.
EC by growth stage
| Stage | EC Target (mS/cm) | Equivalent ppm (700 scale) | Key Rule |
|---|---|---|---|
| Germination | 0.0–0.5 | 0–350 | Germinate in plain pH-adjusted water or very weak solution only |
| Seedling (days 7–14) | 0.8–1.0 | 560–700 | Young roots are sensitive — full-strength nutrients cause stunting at this stage |
| Active growth (days 14–35) | 1.2–1.6 | 840–1120 | Main feeding window; check every 3–4 days and top up with plain water if EC rises above 1.8 |
| Pre-harvest (final 5–7 days) | 1.0–1.2 | 700–840 | Reducing EC slightly in the final week improves flavour and reduces leaf bitterness |
Key nutrient targets for leafy greens and herbs
| Nutrient | Target ppm (active growth) | Deficiency Symptom |
|---|---|---|
| Nitrogen (N) | 100–150 | Pale yellow older leaves; slow growth |
| Phosphorus (P) | 30–60 | Purple-red underside on older leaves |
| Potassium (K) | 150–200 | Brown edges on outer leaves; weak stems |
| Calcium (Ca) | 80–120 | Tip burn — brown papery edges on young inner leaves |
| Magnesium (Mg) | 30–50 | Interveinal yellowing on older leaves |
| Iron (Fe) | 1–3 | Yellow new growth with green veins — almost always a pH problem, not a missing element |
Common Kratky problems and how to fix them
Most Kratky problems are caused by one of three things: incorrect pH, light reaching the reservoir, or water temperature above 22°C. This table covers every common symptom and gives the correct fix — not just a description of the problem.
| Problem | Likely Cause | Fix | Prevention |
|---|---|---|---|
| Tip burn (brown papery inner leaf edges) | Calcium deficiency at leaf margins caused by poor airflow, not a missing element | Add a small fan directed at the canopy; verify calcium is 80–120 ppm in your nutrient formula | Maintain continuous airflow; use a leafy-green formula with Ca-Mg included; keep EC 1.0–1.6 |
| Yellow older leaves (uniform) | Nitrogen deficiency — usually caused by EC below 1.0 mS/cm at the active growth stage | Check EC; if below 1.0, drain and remix at EC 1.2–1.5; always verify pH first | Start at correct EC for the growth stage; mix solution fresh for each grow |
| Yellow new growth with green veins | Iron or manganese lockout caused by pH above 6.5 — the element is present but unavailable | Check pH first; lower to 5.8–6.2 before adjusting nutrients; do not add iron before pH is corrected | Monitor pH every 3–4 days; calibrate meter monthly with fresh buffer solution |
| Brown edges on outer leaves | EC too high (above 1.8) causing osmotic stress on leaf margins, or potassium deficiency | Add plain water to dilute EC back to 1.2–1.5; check potassium is 150–200 ppm in formula | Size reservoir correctly so topping up with nutrients is never needed; check EC at setup |
| Algae in the reservoir (green water) | Light penetrating the container through transparent walls, cracks in the lid, or gaps around net pots | Drain and clean with diluted hydrogen peroxide (3%); rinse thoroughly; seal all light leaks with black tape or foil | Use opaque containers only; check for light leaks before every fill by shining a torch at joints |
| Brown, slimy roots (root rot) | Water temperature above 22°C reducing dissolved oxygen, light reaching roots, or algae presence | Replace solution fully; move to cooler location (18–21°C); add beneficial bacteria (e.g. Hydroguard at label rate) | Insulate reservoir from heat; keep water at 18–21°C; eliminate all light from the reservoir |
| Wilting despite solution present | Root rot has cut off water uptake, or air gap too small (below 2 cm) causing oxygen starvation | Inspect roots — if brown and slimy, replace solution and treat; if air gap is under 3 cm in warm room, lower the solution level slightly | Monitor root health weekly; do not overfill the reservoir at setup |
| Bitter-tasting harvest | EC above 2.0 from repeated nutrient top-ups, or heat stress and bolting before harvest | In the last 5–7 days, replace 30–40% of solution with plain water to bring EC down; harvest before bolt stalks appear | Top up with plain water only; harvest loose-leaf types before the plant reaches 10–12 weeks |
Kratky vs DWC vs NFT vs wick systems
Understanding where Kratky sits relative to other hydroponic methods helps you choose the right system for your setup — and know when to graduate to something more complex as your growing scales up.
| System | Electricity Needed | Setup Cost | Growth Speed | Best For | Main Limitation |
|---|---|---|---|---|---|
| Kratky | None (beyond optional light) | Very low — under £20 for 4–6 plants | Good — 30–50 days for leafy greens | Beginners, off-grid, small batches, herbs and greens | Not suited to large-scale or continuous harvest; not ideal for fruiting crops |
| DWC (Deep Water Culture) | Yes — air pump runs 24/7 | Low-medium — £30–£80 for basic setup | Faster — 24–40 days for leafy greens | Home growers who want faster results; stepping stone from Kratky | Pump failure kills plants quickly; ongoing electricity cost |
| NFT (Nutrient Film Technique) | Yes — pump runs continuously | Medium-high — £80–£500+ | Fastest — 22–35 days for leafy greens | Commercial growers; continuous harvest at scale | Blockages damage crops; complex setup; not beginner-friendly |
| Wick system | None | Very low — similar to Kratky | Slow — passive wicking limits nutrient delivery rate | Very small plants and herbs; truly minimal setups | Slowest growth rate of any hydroponic system; not suitable for larger plants |
In practical terms: start with Kratky, move to DWC when you want faster results or more plants, and consider NFT only if you’re producing 20+ plants per cycle on a repeating schedule. The nutrient and pH knowledge you build in Kratky transfers directly to every other system.
Common Kratky mistakes beginners make
- Submerging the net pot in the solution at setup. Filling the reservoir so that the net pot sits fully submerged from day one floods the growing medium, prevents the air gap from forming, and suffocates roots before they’ve grown long enough to access the oxygen zone. The starting solution should just graze the net pot bottom — 1–2 cm of contact is enough.
- Adding nutrient solution when topping up. This is the most damaging ongoing mistake in Kratky. Plain pH-adjusted water is all that should ever go into a reservoir that is already running. Nutrients top up with EC, not with water — adding concentrate raises the concentration above the intended level permanently.
- Not checking pH after mixing nutrients. Hydroponic nutrient concentrates almost always drop the solution pH below 6.0 — sometimes as low as 4.5 at high dilutions. Never fill a Kratky reservoir without testing and adjusting pH after the nutrients are fully dissolved. A 30-second check prevents weeks of pH-induced deficiency symptoms.
- Choosing a container that is too small. A 500 ml jar runs dry in under two weeks — well before most crops are harvest-ready. The reservoir must hold enough solution to last through the full grow cycle. Use the crop table above to select the correct volume before you start, or verify with our reservoir size calculator.
- Using a translucent container without light-proofing it. Many growers use clear or semi-opaque jars and find algae growing within a week. Even coloured plastic allows enough light through to trigger algae growth when placed near a window or under grow lights. Wrap the outside completely in black plastic, foil, or black tape before the first fill.
- Growing fruiting crops in small containers with no plan for EC drift. A tomato or pepper plant in a 3 L container will drain it within a week and the concentrated salt residue will burn roots. Fruiting crops need 8–15 L minimum per plant and regular monitoring — they are not set-and-forget crops in Kratky.
Frequently asked questions about the Kratky method
No — the Kratky method works without any pump or air stone. The air gap that forms as plants consume the solution provides passive oxygen delivery to the root zone. Adding an air pump technically converts the system into a deep water culture setup. The absence of a pump is the defining characteristic of Kratky and the reason it requires no electricity beyond a grow light. That said, in rooms above 22°C where dissolved oxygen levels drop naturally, a small air stone can help prevent root rot — though this is a modification rather than a standard Kratky setup.
You can top up with plain, pH-adjusted water — but never with nutrient solution. The ideal Kratky system is sized so the reservoir lasts until harvest without any top-up required. If the solution level drops very low before the plant is ready, adding plain water restores the level without raising EC above the intended concentration. Adding nutrient concentrate stacks EC higher with every top-up, eventually causing osmotic stress and bitter flavour. Use our reservoir size calculator to size your container correctly and avoid mid-grow top-ups altogether.
The best container is the smallest opaque vessel that holds enough solution for your crop to reach harvest. For a single loose-leaf lettuce plant, a 2–3 L opaque plastic container or a light-proofed mason jar is ideal. For 4–6 plants, a 20–40 L opaque plastic storage tote with a drilled lid is the most cost-effective option. The container must be completely opaque — no light should penetrate to the nutrient solution. If you’re using a transparent container, wrap the entire outside in black plastic or foil before adding solution. Avoid metal containers, as they can corrode and contaminate the nutrient solution.
The optimal air gap in an established Kratky system is 4–6 cm — measured from the water surface to the underside of the net pot lid. In the first week after transplant, the gap may only be 1–2 cm as the solution level has not yet dropped significantly. This is normal. A gap below 3 cm in rooms above 20°C provides insufficient oxygen to roots and can cause stress symptoms within 48 hours. A gap above 8 cm in the first two weeks risks drying out the upper roots before they’ve grown deep enough into the solution. No intervention is needed when the gap falls within the 4–6 cm target range.
Yes, but tomatoes are significantly more demanding in Kratky than leafy greens. Dwarf or compact varieties like “Tiny Tim” or “Tumbling Tom” work best and need 10–15 L reservoirs per plant. Standard tomato varieties need 20 L or more and will require one or two plain-water top-ups during the grow cycle. EC should be maintained at 2.0–3.5 mS/cm during fruiting, which is much higher than the range used for leafy greens. Tomatoes also need vertical support above the lid and more careful temperature management than passive passive leafy green Kratky. Beginners should grow at least two successful lettuce cycles before attempting tomatoes.
The timeline depends heavily on the crop. Loose-leaf lettuce takes 28–38 days from transplant, or 35–48 days from seed. Basil is ready in 25–35 days from transplant. Full butterhead lettuce heads take 40–55 days. Fruiting crops like peppers take 70–90 days to first harvest. These timelines assume correct pH (5.8–6.2), correct EC for the variety, and 14–16 hours of adequate light per day. Poor light — including insufficient window light in winter — is the most common cause of extended grow times in home Kratky setups.
Yes, but with additional precautions. Outdoor Kratky setups face two risks that indoor grows don’t: rainwater diluting the nutrient solution and raising the water level (which can submerge the air gap and drown roots), and temperature fluctuations affecting water temperature and dissolved oxygen. Use a secure, well-fitting lid to prevent rainwater entry, and place containers in partial shade to prevent water temperature rising above 22°C. Inspect pH and EC more frequently outdoors — every 2 days rather than every 3–4 — because environmental variability affects solution chemistry faster than a controlled indoor environment.
Both Kratky and DWC suspend plant roots above a nutrient solution, but DWC uses a continuously running air pump and air stone to oxygenate the solution and keep the entire root system submerged. Kratky has no pump — the natural air gap provides oxygen to the upper roots while the lower roots stay in solution. DWC grows plants 5–15% faster than Kratky for most leafy crops because dissolved oxygen levels in the solution are higher. Kratky is more reliable in the sense that there are no moving parts to fail — a power cut or pump failure in DWC can kill plants within hours, while Kratky is unaffected by electricity outages.
Getting started with your first Kratky system
The Kratky method is the most genuinely beginner-accessible form of hydroponics — not in the sense of being dumbed down, but in the sense that the barriers to a successful first grow are lower than any other system. You need a container, some nutrient solution, a pH meter, and seeds. The plant does the rest.
The three things that consistently separate successful Kratky grows from failed ones are: pH held at 5.8–6.2 from the first fill, a reservoir sized correctly for the crop, and the discipline to top up only with plain water rather than nutrient solution. Everything else — algae prevention, tip burn management, temperature control — follows from getting those three fundamentals right.
Start with loose-leaf lettuce in a 2–3 L opaque container. Check pH and EC before filling. Give it 14–16 hours of light per day. In 30–38 days, you’ll have your first hydroponic harvest — and the direct experience of how the system works, which makes every subsequent grow easier. Use our nutrient calculator to mix your first batch correctly, and our reservoir size calculator to confirm you’ve chosen the right container before you start.
For a dedicated guide to growing lettuce specifically in Kratky — covering variety selection, container sizing, and harvest techniques in detail — see our Kratky lettuce guide. For the full landscape of hydroponic systems and how Kratky fits within it, our Complete Hydroponics Guide covers everything from beginner to intermediate level.
