How long does one Kratky jar last?

Transplant to harvest runs about a month for loose-leaf greens, up to six weeks for a dense head. After cutting, you rinse the jar, mix fresh solution and start again, since the hardware is reusable.

Can I scale the Kratky method beyond a jar?

Yes. A lidded tote with several net-cup holes grows six or more heads on the same passive principle without plumbing. Beyond that, most growers switch to an active system for faster turnover and tighter control.

The Kratky Method: Passive Hydroponics You Can Start for $15

Q: Does the Kratky method really need no electricity?

Correct. There is no pump, air stone or timer in the design. The only power involved is a grow light, and only if your spot lacks a bright window, which makes it the cheapest hydroponic entry point.

Q: Why is my Kratky lettuce yellowing?

Usually a pH drift outside 5.5-6.5, which locks nutrients away even in a full jar, or a reservoir that ran dry early. Yellow lower leaves often mean nitrogen is not reaching the plant rather than a need for more food.

Updated July 2026 · Editorial team · Topic: hydroponics

The Kratky Method: Passive Hydroponics You Can Start for $15 — Hydroponics

A retired biology professor at the University of Hawaii, B.A. Kratky, published a method in 2009 so stubbornly simple it feels like cheating: put a plant in a jar of nutrient water, walk away, come back in a month, eat a salad. No pump. No electricity. No timer. No daily fuss. People assume something that cheap must grow sad, stunted lettuce. It doesn't — and understanding why is the whole trick.

Short answer: A complete Kratky setup costs about $15 — a wide-mouth jar, a net cup, clay pebbles, and a bottle of two-part nutrients. One quart-to-half-gallon jar grows one head of leaf lettuce in 30–45 days with zero electricity. The catch is a hard one: you never top up the water, and it only works for fast, non-fruiting crops.

Reviewed by the BackyardStead Lab editorial team. We publish real ROI, plain numbers and USDA/extension data so you can judge for yourself — we run the math, not a farm. Educational information only: backyard-chicken and livestock rules vary by city, home canning must follow USDA/NCHFP-tested methods (botulism risk), and mushrooms should be grown only from a known-species kit — never foraged on our word.

How growing with a shrinking water level works

Most hydroponics obsess over pumping air to the roots. Kratky solves oxygen with laziness instead. You fill the jar so the net cup's bottom just touches the solution. As the plant drinks, the water level drops — and the gap it leaves behind fills with humid air. The roots split into two crews: the lower "water roots" keep feeding, while the upper roots dangle in that air pocket and breathe. By harvest, the jar is nearly empty and the plant is full-size. The falling water line is the feature, not a problem to fix.

What it costs to start

Item	Cost	Notes
Wide-mouth jar or tote	$0–6	A recycled pickle jar is free; a lidded tote scales it up
Net cup (2–3 in)	$0.30 each	Sold in packs of 25–50 for a few dollars
Clay pebbles (hydroton)	$8–15/bag	One bag lasts dozens of grows and rinses reusable
Two-part nutrients	$15–25	A quart set makes many gallons of solution
pH test kit	$10–15	Optional but strongly recommended

Amortized across a bottle of nutrients and a bag of pebbles, the marginal cost of jar number two is basically the net cup and a seed. Search "net cups 2 inch" and "hydroponic clay pebbles" rather than pricey branded starter kits — the loose supplies cost a fraction and outlast any single grow.

Step by step, once

Sprout a seed in a rockwool cube or a rinsed sponge plug until roots peek out the bottom (5–10 days).
Mix your solution to the label rate for leafy greens, roughly 500–700 ppm, and adjust to pH 5.5–6.0.
Set the net cup in the lid, cradle the cube in clay pebbles, and fill the jar until the solution kisses the bottom quarter-inch of the cup.
Block the light on the reservoir — wrap the jar in foil or use an opaque tote — or algae will bloom in the nutrient soup.
Leave it. Bright light 12–16 hours a day, and do not refill. The plant finishes the water on schedule.

Data note: The ppm and pH targets above match published hydroponic ranges for leafy greens, and the 30–45 day window reflects seed-packet maturity for loose-leaf types grown under adequate light. We're compiling those figures, not reporting a jar on our own windowsill — your timeline shifts with light intensity and room temperature.

What actually grows this way — and what doesn't

Kratky rewards crops that finish before they run out of water and drown their remaining roots. It punishes anything long-season or thirsty.

Excellent: loose-leaf and butterhead lettuce, basil, cilantro, bok choy, kale, chard, mustard greens. All harvest in 4–7 weeks.
Workable in a big jug: a single determinate cherry tomato or pepper — but only in a 2–5 gallon reservoir, and results are inconsistent because fruiting plants drink faster than the method likes.
Skip it: anything you harvest for months. Full-size tomatoes and cucumbers outlast the static water and want the constant feeding covered in the DWC bucket setup.

Beginner mistakes, in numbers

Filling above the net cup all the way up. Drown every root and there's no air pocket to breathe from. Leave a 1–2 inch gap between the starting waterline and the cup base for the plant to grow into.
Using a jar under 1 quart for lettuce. A full head needs roughly 0.5–1 gallon of solution to finish. Too little water and it bolts or starves halfway.
Leaving the reservoir clear. Sunlight plus nutrients equals a green algae film in days that competes with your roots for oxygen. Opaque containers only.
Refilling mid-grow. Top it back up and you erase the air gap the roots depend on. If you find yourself refilling, you've picked a crop that belongs in an active system, not a passive one.

FAQ

Does the Kratky method really need no electricity?

Correct — none at all. There's no pump, air stone, or timer anywhere in the design. The only power involved is a grow light, and only if your spot lacks a bright window. That's what makes it the cheapest possible entry point.

How long does one jar last?

From transplant to harvest runs about a month for loose-leaf greens, sometimes up to six weeks for a dense head. Once you cut it, you rinse the jar, mix fresh solution, and drop in the next seedling — the hardware is fully reusable.

Why is my Kratky lettuce yellowing?

Usually a pH drift out of the 5.5–6.5 band, which locks nutrients away even in a full jar, or a reservoir that ran dry too early. Yellowing lower leaves often means nitrogen isn't reaching the plant, not that it needs more food added.

Can I scale Kratky beyond a jar?

Yes. A lidded storage tote with several net-cup holes grows six or more heads on the same passive principle, no plumbing added. Beyond that scale, most growers switch to an active system for faster turnover and tighter nutrient control.

Related:

Educational information only, not professional horticultural or dietary advice. BackyardStead Lab does not operate a commercial farm or laboratory; figures here are compiled from USDA, university extension publications and published grower data. Yields, prices and payback periods vary with climate, cultivar, water quality and local costs.