Building a DIY hydroponic system for under $100

Store-bought indoor gardens cost roughly $100 to $900, not counting pods. Yet the principle fits in one sentence: roots in nourished water, under good light. With the method developed by researcher Bernard Kratky at the University of Hawaii, you do not even need a pump: the plant does the work on its own.

Here is the method in 30 seconds, the shopping list with prices checked on October 21, 2026, at Canadian retailers, the step-by-step assembly and the mistakes to avoid. To compare with store-bought devices, see our guide to smart indoor gardens.

The Kratky method in 30 seconds

In a paper published in 2009 in Acta Horticulturae, Kratky describes three "non-circulating" methods for growing lettuce. They need no electricity, pump, aeration or wick. The principle:

• All the nutrient solution is added at the start, before planting.
• As the plants drink, the level drops. This creates a moist air space that grows under the lid.
• The roots share the work: those in the moist air mainly serve to breathe, while those in the solution drink and feed.

Hence the golden rule: never raise the solution level. Drowning the air roots can kill the plant, Kratky warns. For lettuce, he allows 4 to 8 L of solution per plant in his covered tank model. His plastic storage containers or ice chests held 6 to 8 plants.

The shopping list

Prices checked online on October 21, 2026, before taxes. These are examples: equivalent products can be found at most hardware stores and garden centres.

So the $100 mark holds if you reuse a bin and already have a timer, or a smart plug. Otherwise, count on $106.77. The good news: the light, timer, pots and bin carry over from one winter to the next, and a bottle of concentrate normally makes several bins of solution: check the dose on the label. The second winter costs little more than seeds and electricity.

Why a shop light rather than a "grow light"? Because Iowa State University specifically lists a 4-foot LED shop light among the ways to light a collection of herbs, and it covers a large bin for less money. Its drawback: like most lights sold at hardware stores, it does not list its plant-useful photon output. We explain how to read those numbers in LED grow lights: reading the real specs.

Step-by-step assembly

1. Prepare the bin

Choose an opaque bin: light that reaches the solution grows algae, and Kratky recommends covering or darkening containers to discourage it. If your bin is translucent, wrap it in cardboard or aluminum foil. Wash it with soapy water and rinse well. Work out the volume: for 6 lettuces, at 4 to 8 L per plant, you need 24 to 48 L of solution.

2. Cut holes in the lid

Trace the outline of the net pots on the lid and cut holes slightly smaller than their rims, so they stay suspended. Space them about 15 cm apart to let the leaves spread out. A drill with a hole saw does a clean job; a utility knife works too, with some patience.

3. Prepare the solution

Fill the bin almost to the top with water, as Kratky does before setting in his plants. Then add part 1, stir, then part 2, and stir again, at the dose shown on the label for leafy greens. Never mix the two concentrates directly together: pour them into the water separately. Kratky did the same, with two stock solutions added separately. Then store the bottles out of children's reach.

4. Set the pots and the level

Fill the net pots with moist seed-starting mix. In his work, Kratky used mixes of peat, perlite and vermiculite. Put the lid on and slide the pots into the holes: in his covered tank, only the bottom 1 to 2 cm of the pots sits in the solution. The mix wicks up moisture from below and stays damp on its own. From then on, leave the level alone: it will drop as the roots grow toward the bottom.

5. Sow

Kratky either seeded directly into the pots or transplanted 1- to 2-week-old lettuce seedlings into them. The simplest approach: sow 2 or 3 seeds per pot, barely covered for lettuce, then thin to keep only the best plant in each pot.

6. Install the light

Hang the light from small chains, 15 to 30 cm (6 to 12 in) above the leaves, and plug it into a timer for 12 to 16 hours a day, as Iowa State recommends. Raise it as the plants grow. A 4-foot light overhangs an ordinary bin: put two bins side by side, or add a few pots of herbs in soil under the same light.

7. Harvest

In Kratky's trials, under the Hawaiian sun, lettuce was harvested about 30 to 40 days after transplanting. Under a light, in winter, be patient. You can also pick the outer leaves as you go.

Mistakes to avoid

• Raising the level. It is the classic mistake. If the solution drops too fast, the bin was too small for the number of plants: go bigger next time.
• A bin that lets light through. Algae guaranteed. Also plug any unused holes.
• Ordinary garden fertilizer. Without soil, the plants depend entirely on the solution. Kratky used a complete hydroponic fertilizer; a nutrient designed for hydroponics contains the calcium and trace elements plants need.
• Poor water quality. Kratky warns that in water high in salts, the concentration rises as the plants drink; where water quality is poor, he recommends rainwater.
• Reusing the solution forever. Kratky advises draining and refilling the tank at least every three crops, and more often if water quality is poor.
• Electricity near water. Keep the light, the timer and the power bar above the level of the bin, away from splashes, and ideally plug them into an outlet protected by a ground fault circuit interrupter (GFCI), like the ones in bathrooms.

Lettuce or basil: where to start?

Start with lettuce: it is the crop Kratky's work focuses on, it grows fast and it handles the method well. A butterhead lettuce like 'Buttercrunch' is ready about 55 days after sowing in conventional growing, according to its seed company.

Basil works too, but it stays in place much longer and drinks more. Give it the top of Kratky's range, about 8 L of solution per plant, and keep it warm: cold can damage its leaves at 10°C, according to the University of Illinois. Once your first bin is running smoothly, you can try a growing wall: see our guide to the DIY vertical garden, or, for the more ambitious, aquaponics basics, where fish fertilize the water.

How much does it cost to run?

With the Kratky method, only the light uses power. The 48 W shop light, on for 16 hours a day, uses 0.768 kWh a day. At Hydro-Québec's Rate D, in effect since April 1, 2026, that is 5.4 to 8.6¢ a day depending on whether your kWh costs 7.065¢ or 11.142¢, or $8.19 to $12.92 for a full 151-day winter, before taxes. We cover every case, including the heat the light gives back to your home, in what a winter of herbs under LEDs costs.

Sources

• Three Non-circulating Hydroponic Methods for Growing Lettuce, B. A. Kratky, Acta Horticulturae 843, University of Hawaii, 2009.
• How can I provide more light for my herbs indoors?, Aaron Steil, Iowa State University Extension, 2024.
• Basil, Illinois Extension, University of Illinois.
• Nursery Pots (Mesh) (product page), The Seed Company by E.W. Gaze, accessed October 21, 2026.
• Terreau de démarrage pour semis biologique (product page, in French), Fafard, Pépinière.ca, accessed October 21, 2026.
• Basilic bio 'Grand Vert' (product page, in French), W.H. Perron, Pépinière.ca, accessed October 21, 2026.
• Laitue boston 'Buttercrunch' bio (product page, in French), Norseco, Pépinière.ca, accessed October 21, 2026.
• Root Farm Part 1 Base Nutrient 473 ml (product page), Kent, accessed October 21, 2026.
• Root Farm Part 2 All-Purpose Nutrient 473 ml (product page), Kent, accessed October 21, 2026.
• Root Farm Concentrated Liquid All-Purpose Base Nutrient Part 1 (product page), Do it Best, accessed October 21, 2026.
• DYMOND 4 ft. LED Shop Light 48W (product page), Home Depot Canada, accessed October 21, 2026.
• Defiant Indoor 24 Hour Mechanical Timer (product page), Home Depot Canada, accessed October 21, 2026.
• Grille tarifaire au 1er avril 2026 (rate grid, in French), Hydro-Québec, 2026.