Published: April 2026 | Reading time: 8 minutes | Difficulty: Complete beginner
If you’ve ever bought a basil plant from Tesco, kept it on the windowsill for three days, and watched it slowly die — you’re not alone. Supermarket herbs are notoriously short-lived, grown in cramped pots with barely any root space or nutrients. The good news? There’s a ridiculously simple way to grow your own basil indoors that costs almost nothing and keeps producing for months.
It’s called the Kratky method, and it might be the easiest thing in hydroponics.
No pumps. No electricity. No complicated setup. Just a jar, some water, a handful of supplies — and fresh basil whenever you want it.
What Is the Kratky Method?
The Kratky method is a type of passive hydroponics — meaning the plants grow in nutrient-rich water, with no pumps or moving parts required. It was developed by Dr. Bernard Kratky at the University of Hawaii, and it’s become hugely popular with home growers because of how beginner-friendly it is.
Here’s the core idea: you suspend a plant in a net cup (a small mesh pot) above a container of nutrient solution. The roots hang down into the water. As the plant drinks, the water level drops — and this naturally creates an air gap between the roots and the surface of the water. That air gap is crucial. It gives the roots the oxygen they need to stay healthy.
The beauty of it? You set it up once, top it up occasionally, and the system largely takes care of itself.
Basil is one of the very best plants to start with using this method. It grows enthusiastically in hydroponics, produces continuously for months, and — in the UK where supermarket basil costs £1.50 a packet and lasts three days — the economics are immediately compelling.
What You’ll Need
The full shopping list costs between £15 and £25. You can get everything on Amazon.
The essentials:
- A mason jar or opaque container — a standard 1-litre mason jar works perfectly. If the jar is clear, wrap it in black tape or foil to block light and prevent algae from growing.
- Net cups (2-inch) — small mesh pots that hold your plant. A pack of 50 costs about £5 and will last you years.
- Hydroponic nutrient solution — General Hydroponics Flora Series is the industry standard and what most beginners use. Mix at half-strength for herbs.
- A growing medium — clay pebbles or rockwool cubes to support the plant in the net cup. Either works fine for beginners.
- Basil seeds or a seedling — Genovese or Sweet Basil are ideal. You can start from seed or buy a supermarket basil plant and use it as your starter.
- A pH testing kit — you want your water between pH 5.5 and 6.5. A cheap test kit from Amazon is fine to start with.
Optional but helpful:
- A grow light — essential in the UK from October to March, when window light is too weak for herbs. A basic LED panel costs £20–£35.
Want to skip the setup? If you’d rather not source the parts separately, the iDOO 12-Pod Indoor Garden (around £69 on Amazon) is an all-in-one kit with a built-in grow light that uses a similar method. It’s plug-and-play, requires no measuring or mixing, and is a great option if you want to get growing immediately.
Step-by-Step: Setting Up Your Kratky Basil Garden
Step 1: Prepare Your Container
Fill your mason jar or container about two-thirds full with water. Add your hydroponic nutrients at half the recommended strength — for basil, this is plenty. Mix well.
Check the pH. Aim for between 5.5 and 6.5. If it’s too high, you can use a small amount of pH Down solution (a bottle lasts a very long time). If too low, use pH Up. For most UK tap water you’ll likely need to bring the pH down slightly.
Step 2: Prepare Your Plant
If you’re starting from seed, soak a rockwool cube in pH-balanced water, insert a seed, and keep it somewhere warm (above 20°C) until it germinates — usually 5 to 10 days. Once you have two or three true leaves, it’s ready to transfer.
If you’re using a supermarket basil plant, gently wash all the soil off the roots under lukewarm water. This takes patience — you want as little soil as possible remaining. Separate individual stems if the pot contains multiple plants.
Step 3: Set Up the Net Cup
Place your plant in the net cup. Fill around the roots and stem with clay pebbles to support it. The plant should be stable and upright.
Place the net cup in the mouth of the jar. The bottom of the cup should just touch the surface of the nutrient solution — or be a centimetre above it at most. The roots will quickly grow down into the water.
Step 4: Find the Right Spot
Basil needs 12 to 16 hours of bright light per day. In the UK, a south-facing windowsill works well from April to September. For the rest of the year — or if you don’t have a sunny window — you’ll need a grow light positioned 15 to 30cm above the plant.
Basil also dislikes cold. Keep it somewhere above 15°C. Avoid windowsills in winter where the glass makes the air cold at night.
Step 5: Maintain Your Setup
Check the water level every few days when starting out. As the plant establishes itself, you’ll notice the level dropping — this is the system working exactly as intended.
Top up with fresh nutrient solution (at the same half-strength concentration) when the level drops by about a third. Don’t overfill — the air gap between the water and the roots is important.
Every two to three weeks, do a full water change to prevent salt build-up and pH drift. This takes about five minutes.
Harvesting Your Basil
This is where it gets satisfying. Basil is a cut-and-come-again plant, meaning the more you harvest, the more it grows.
The right way to harvest:
- Always cut just above a pair of leaves (a “node”)
- Never take more than a third of the plant at one time
- Harvest from the top down — this encourages the plant to bush out rather than grow tall and leggy
- Remove any flower buds as soon as they appear — once basil flowers, the leaves turn bitter and the plant starts to die off
Done correctly, a single Kratky basil plant will produce continuously for three to four months. One plant supplies the equivalent of around £30 to £50 worth of supermarket basil over its productive life.
Troubleshooting Common Problems
Yellow leaves Usually a sign of nutrient deficiency or pH being off. Check your pH first — this solves most yellowing issues. If pH is fine, try increasing your nutrient concentration slightly.
Leggy, stretched growth The plant is reaching for light. Move it closer to a window or lower your grow light. Basil needs intense light, not just brightness.
Algae in the jar Green slime means light is getting into your nutrient solution. Make sure the container is fully covered or opaque. This won’t kill the plant but wastes nutrients and looks unpleasant.
Roots turning brown Some browning is normal as roots age. If the plant looks healthy above the water, don’t worry. If leaves are yellowing too, try a full water change with fresh nutrient solution.
Leaves turning bitter The plant has started to flower. Remove the flower stalks immediately and harvest heavily to slow the process. Once a basil plant has fully bolted (gone to seed), it won’t recover — start a new one.
How Much Does It Cost vs Buying from a Supermarket?
Here’s the honest comparison for UK shoppers:
Supermarket basil: £1.50 per pot, lasts 3–5 days, one pot’s worth of leaves.
Kratky basil: £15–25 setup cost then pennies, lasts 3–4 months, continuous harvests worth £30–50.
After your initial setup, each subsequent grow costs roughly £1 to £3 in nutrients and electricity. The system pays for itself within the first month.
Ready to Try a Bigger Setup?
Once you’ve got one or two Kratky jars working, the natural next step is an all-in-one countertop system. The iDOO 12-Pod and the Click & Grow Smart Garden 9 both use similar passive growing principles but add built-in LED lighting, more growing pods, and a more polished look for the kitchen. We’ve reviewed both in our best hydroponic kits for beginners UK guide.
For a south-facing windowsill in summer, though? A few mason jars and a packet of seeds will absolutely do the job.
Summary
The Kratky method is the perfect entry point into hydroponics for UK beginners. It costs very little, requires no complicated equipment, and basil is one of the most forgiving and rewarding plants to start with.
What you need: mason jar, net cup, nutrients, growing medium, basil seeds.
What you don’t need: pumps, electricity, prior experience, a garden, or a green thumb.
Start with one jar on a sunny windowsill. If it works — and it very likely will — you’ll understand more about how plants actually grow than you ever did from soil gardening. And you’ll never pay £1.50 for a supermarket basil plant again.
IndoorGrowGuide earns a small commission on products recommended in this article, at no extra cost to you. We only recommend products we’d genuinely use ourselves.
Related guides:
- Best Hydroponic Kits for Beginners UK 2026
- iDOO vs Click & Grow: Which Indoor Garden Wins?
- Best LE Grow Lights for Herbs UK
- The Complete Beginner’s Guide to Indoor Hydroponics UK