Kratky Jar Setup in Under 10 Minutes: Complete Beginner Guide

A kratky jar setup is the fastest way to go from zero experience to a working hydroponic system. In under 10 minutes of active assembly time, you can build a passive growing system that produces fresh lettuce, basil, or herbs with no pump, no electricity, and no daily maintenance.

This guide gives you the exact steps, exact measurements, and exact timings for a successful kratky jar setup. No guesswork, no vague instructions, no assumptions about what you already know. If you can follow a recipe, you can do this.

What you need for your kratky jar setup

Gather everything before you start. The assembly itself takes under 10 minutes, but hunting for materials mid-build wastes time and creates frustration.

• One wide-mouth mason jar (1 litre recommended for first grow). Any wide-mouth jar works — old jam jars, coffee jars, or food storage containers. The opening needs to be wide enough for a 3-inch net pot to sit in without falling through.
• One 3-inch net pot (approximately 50p on Amazon or £3-5 for a 10-pack).
• A handful of clay pebbles (LECA) — enough to fill the net pot. A small bag costs £3-5 and fills 6-10 net pots.
• Hydroponic nutrients — any beginner brand works. Formulex is the simplest (one bottle, one measurement). General Hydroponics Flora Series is more versatile. Either costs £8-12 and lasts months.
• pH test drops — £4-6 for a kit with hundreds of tests.
• pH Down solution — £3-5 for a bottle lasting months.
• Aluminium foil — to wrap the jar and block light from reaching the nutrient solution.
• A pre-germinated seedling — started 7-10 days earlier on a damp paper towel or in a rock wool cube. The seedling should have its first set of true leaves (the second pair that appears after the initial rounded seed leaves).

Total cost for your first kratky jar setup: approximately £15-20. After this initial purchase, each additional jar costs just £1-3 because you already own the nutrients, pH supplies, and clay pebbles.

Pre-setup: germinating your seeds (7-10 days before)

You need a seedling ready before you can complete your kratky jar setup. Start this step 7-10 days before you plan to assemble the jar.

Dampen a paper towel until it is thoroughly moist but not dripping. Fold it in half and place it on a small plate or saucer. Place 2-3 seeds on the surface. For lettuce, leave them uncovered because lettuce seeds need light to trigger germination. For basil, press them lightly into the surface without burying them.

Cover the plate loosely with cling film or slip it into an unsealed plastic bag. This traps moisture while allowing air exchange. Place in a warm spot: a kitchen counter, the top of a router (gentle warmth), or near (not on) a radiator. Ideal temperature is 20-25°C.

Check daily. Mist with a spray bottle if the paper towel surface begins to dry out. Keep it consistently damp but not waterlogged. Soggy conditions encourage mould; dry conditions kill the germinating seed.

Lettuce germinates in 3-5 days. Basil takes 5-10 days. You will see a tiny pale stem appear first, followed by two small rounded seed leaves (cotyledons). Wait until the first pair of true leaves develops (they look different from the seed leaves — more textured and shaped like the adult plant’s leaves). This typically happens 7-14 days after sowing. Your seedling is now ready for the kratky jar setup.

The 10-minute kratky jar setup (step by step)

Minute 1-2: Wrap the jar

Tear off a piece of aluminium foil large enough to wrap completely around your jar with some overlap. Press the foil tightly against the glass, folding the edges neatly at the top and bottom. The goal is to block all light from reaching the nutrient solution inside. Light causes algae growth, which competes with your plant for nutrients and turns the water green.

Cover the bottom of the jar as well. Light can reflect off surfaces and enter from below. A thorough foil wrap takes 60-90 seconds and prevents the single most common cosmetic issue in kratky growing.

If you want a more attractive kratky jar setup, paint the jar with acrylic paint (any dark colour) instead of using foil. This looks much better on a kitchen windowsill and blocks light just as effectively.

Minute 2-3: Check the net pot fit

Place the 3-inch net pot in the jar opening. The lip of the net pot should rest on the rim of the jar, holding the basket portion inside the jar without falling through. The bottom of the net pot should hang approximately 3-5 centimetres below the rim.

If the net pot is too small and falls through, cut a circle of cardboard slightly larger than the jar opening, cut a hole in the centre just big enough for the net pot basket to pass through, and place this cardboard collar on the jar rim. The net pot lip rests on the cardboard instead of the jar rim.

Minute 3-5: Mix the nutrient solution

Remove the net pot temporarily. Fill the jar with room-temperature tap water to approximately 1 centimetre below where the bottom of the net pot sits. For a 1-litre jar, this is roughly 700-800ml of water.

Add hydroponic nutrients at half the strength recommended on the product label. For Formulex, half strength is approximately 2.5ml per litre. For General Hydroponics Flora Series, follow the product chart and halve each value. Use a measuring syringe, the bottle cap, or a teaspoon for accuracy.

Stir the solution for 15-20 seconds to dissolve the nutrients completely. The water may change colour slightly (usually to a pale amber or green depending on the brand). This is normal.

Minute 5-7: Test and adjust pH

Using your pH test drops, take a small sample of the nutrient solution in the provided test tube. Add 3 drops of indicator liquid, cap the tube, and shake gently. Compare the colour to the chart included in the kit.

You are aiming for a pH between 5.5 and 6.5. The ideal target is 5.8-6.0. UK tap water typically tests at pH 7.0-8.0, and adding nutrients usually brings it down to approximately 6.5-7.5. You will almost certainly need to add pH Down.

Add pH Down one drop at a time. Stir after each drop. Retest after every 2-3 drops. Approach the target gradually — it is much easier to lower pH in small steps than to overshoot and need pH Up to correct. Once your test shows a colour in the 5.5-6.5 range, you are done.

Remember the golden rule: always add nutrients FIRST, then test pH. Nutrients change the pH of water significantly. If you test plain water, adjust to 6.0, then add nutrients, the pH will shift and you will need to readjust. Mix nutrients first, then test and adjust once.

Minute 7-9: Plant the seedling

Rinse a handful of clay pebbles under running water to remove dust. Fill the net pot approximately one-third full with rinsed pebbles.

Gently lift your seedling from the paper towel. If the roots have grown into the paper towel, that is fine — you can place the entire piece of paper towel into the net pot. The paper towel will decompose naturally and causes no harm. If using rock wool, place the entire rock wool cube with the seedling into the net pot.

Position the seedling in the centre of the net pot, on top of the first layer of pebbles. The roots should point downward. Carefully add more clay pebbles around and over the seedling’s root area, filling the net pot to just below the rim. Leave the stem and leaves fully exposed above the pebbles. The pebbles should hold the seedling upright without crushing the delicate stem. Be gentle.

Minute 9-10: Final assembly and positioning

Place the loaded net pot into the jar opening. The bottom of the net pot should be touching or sitting just barely above the nutrient solution surface. You should be able to see or feel that some solution is wicking up through the clay pebbles. If the solution level is too low to reach the net pot bottom, add a small amount of pH-adjusted nutrient solution until it does.

Place your completed kratky jar setup on your sunniest windowsill. South-facing windows are ideal in the UK, providing 6-8 hours of direct sunlight during spring and summer. East and west-facing windows work adequately, especially from April to September.

If your available light is limited (north-facing window, winter growing, or a room with small windows), add a clip-on LED grow light positioned 15-20 centimetres above the plant. Set a plug-in timer for 14-16 hours on, 8-10 hours off. A basic grow bulb costs £10-15 and fits any desk lamp.

Your kratky jar setup is now complete.

After setup: what to do (and what not to do)

Week 1-2 after transplant

The seedling is establishing itself. Growth above the surface is slow because most energy goes into root development. The water level drops slightly. Your job: observe. Do nothing else. Check once at the end of the week to confirm the plant looks healthy and the roots are growing downward (peek through the foil if curious).

Week 2-4 after transplant

Growth accelerates visibly. New leaves appear every few days. The water level drops steadily and an air gap forms between the surface and the net pot. This air gap is essential — roots growing in this space absorb oxygen. Your job: check once a week. Optionally test pH (should still be in 5.5-6.5 range).

Week 4-6 after transplant

The plant reaches harvestable size. For lettuce, a full rosette of leaves is ready for salad. For basil, dense bushy growth with aromatic leaves ready for cooking. The water level has dropped significantly. This is completely normal and intentional. Your job: harvest and enjoy.

The critical mistake to avoid after your kratky jar setup

Do not refill the jar to the original water level. This is the number one kratky killer. As the water drops, air roots develop in the gap. Refilling submerges these roots, suffocating them. The plant develops root rot and dies from too much water, not too little.

Only add water if roots are no longer touching the solution at all. Even then, add only a small amount of pH-adjusted water (no extra nutrients). Never bring the level back to where it started.

After harvest: resetting for the next grow

Remove the old plant from the net pot. Pull out the spent roots and any decomposed paper towel. Rinse the clay pebbles under running water. Rinse the jar. Mix fresh nutrient solution, adjust pH, and transplant a new seedling. The jar, net pot, and clay pebbles are reusable indefinitely. Your next kratky jar setup takes even less than 10 minutes because you already know the process.

Start your next seedling germinating a week before you expect to harvest the current plant. This way, a new seedling is always ready to go into a freshly reset jar, maintaining your continuous supply of fresh food.