Kratky Method Complete Guide

The Kratky method is hydroponics stripped to its absolute essentials. No pumps. No electricity. No complexity. Just plants growing in nutrient water. It's named after B.A. Kratky, the University of Hawaii researcher who formalised the technique.

## Quick Picks: Kratky Supplies

The honest truth: Kratky is the cheapest way to learn hydroponics. A complete setup costs under £30. Success teaches you principles that apply to every other system.

## How It Actually Works

Fill a container with nutrient solution. Suspend a plant in a net pot so roots reach the water. Leave an air gap between the water surface and the net pot - this is the crucial detail everyone mentions but few explain properly.

As the plant drinks and grows, the water level drops. Roots that were submerged become exposed to air, providing oxygen. New roots grow downward to follow the receding water. The plant essentially regulates itself.

This is why you don't top up the water mid-grow. Maintaining the air gap is more important than maintaining water level. The exposed roots are breathing.

## The Air Gap Is Everything

Roots need oxygen to function. Fully submerged roots in still water will eventually rot - there's not enough dissolved oxygen for long-term health.

The air gap solves this. Upper roots access oxygen from the air. Lower roots access water and nutrients. The plant gets both.

Start with about 2-3cm of air gap below your net pot. As water drops, this gap grows. By harvest, you might have 10cm or more of air roots. This is correct and healthy.

Don't add water to eliminate the gap. Don't panic when levels drop. This is the system working as intended.

## Container Selection

Mason jars: Perfect for single herbs. 1-litre jars work well for basil, mint, parsley. Wrap in foil or paint the outside to block light (algae loves lit nutrient solution).

Storage boxes: Good for multiple plants. 20-40 litre opaque boxes work brilliantly. Cut holes in the lid for net pots. Grow 4-8 plants easily.

5-litre buckets: Excellent for larger plants. One bucket per plant gives enough nutrient volume for tomatoes or peppers, though these push the method's limits.

General rule: Deeper containers hold more solution, which means longer between interventions. A shallow container for a large plant will run dry fast.

## Setting Up Step by Step

1. Prepare your container: Clean thoroughly. If transparent, wrap in foil or cover to block light.

2. Cut or fit net pot holes: The net pot should sit snugly with most of its depth above the lid and 1-2cm below.

3. Mix nutrient solution: Fill container with water, add nutrients at half strength (use measuring syringe for accuracy), adjust pH to 5.5-6.5.

4. Add growing medium: Fill net pot with rinsed clay pebbles or similar inert medium.

5. Position seedling: Place seedling so roots touch or nearly touch the water surface. Roots should extend down through the medium.

6. Create air gap: Water level should be 1-2cm below the bottom of the net pot initially. As roots grow down, they'll reach the water.

7. Place under light: Sunny window or grow light. Herbs need 12-16 hours of light daily.

8. Wait: Seriously. The main intervention is waiting. Check water level occasionally but don't obsess.

## Best Kratky Crops

Excellent (almost guaranteed success): - Lettuce (all varieties) - Basil - Mint - Coriander - Spinach - Rocket - Pak choi - Kale - Swiss chard

Possible (need larger containers): - Cherry tomatoes (5-10L container minimum) - Peppers (5-10L container minimum) - Strawberries - Beans

Difficult (not recommended for beginners): - Large tomatoes (nutrient demands are high) - Cucumbers (need support and lots of nutrients) - Root vegetables (they don't suit soilless growing)

## What to Avoid

Topping up water mid-grow: This eliminates the air gap that formed. Those exposed roots are now drowning. Only add water if the container is nearly empty AND the plant is large enough to have extensive air roots that will survive brief submersion.

Clear containers without covering: Light reaching nutrient solution causes algae. Algae competes with plants for nutrients, clogs roots, and creates smell. Always block light.

**Too strong nutrients:** Seedlings and young plants burn easily. Start at 50% recommended strength. You can increase later if plants look pale or slow.

Tiny containers for large plants: A tomato in a mason jar will exhaust nutrients and water within days. Match container size to final plant size.

Ignoring pH: Even Kratky needs pH management. Test when you set up. Retest weekly if convenient. Adjust if it drifts outside 5.5-6.5.

## The Limitations

Kratky works brilliantly for single-harvest crops (lettuce heads) and cut-and-come-again greens (basil, spinach). It's less ideal for long-term plants.

The nutrient solution doesn't replenish automatically. It doesn't circulate or aerate. Large, hungry plants can exhaust a container's resources.

For tomatoes producing fruit over months, you'll eventually need to intervene - either switching to an active system or carefully topping up nutrients. This moves beyond pure Kratky into hybrid territory.

## Scaling Up

Once you've grown a few successful Kratky plants, scaling is cheap and easy:

Storage box garden: One 40L opaque box with 6 holes produces a continuous salad supply. Stagger planting dates so you're always harvesting something.

Window farm: Multiple mason jars on a bright windowsill. Herbs for cooking, ready whenever you need them.

Grow light shelf: Add a basic LED light and you can grow anywhere regardless of window access. A shelving unit becomes a vertical garden.

## Our Take

Kratky is the best way to learn hydroponics. Period.

Success builds confidence. Understanding develops through observation. You'll see roots growing, watch water levels drop, learn what healthy plants look like before they're healthy. This hands-on knowledge transfers to every other system.

Start with lettuce in a storage box or basil in a mason jar. If it works, you've learned the fundamentals of hydroponics for under £30. If it fails, you've learned something specific about your setup for under £30.

Either way, that's excellent value.

Take our quiz if you want recommendations for your specific space and growing goals.