Gardening & growing · Technical & maker
Hydroponics
Hydroponics is growing without soil: roots sit in water carrying dissolved nutrients, and you supply everything the ground would have. It works, it is genuinely faster than soil for leafy crops, and it is surrounded by more nonsense than almost any hobby in this catalogue. The reason is that two entirely different activities share the name — a jar of basil on a kitchen windowsill and a tented room with a controller in it — and the equipment sold to beginners is frequently designed for the second. This page separates them first, then covers the systems and what each is actually good at, the running costs nobody mentions, the problems that arrive in week three, and the several things we do not publish and why.
Also known as growing without soil, indoor growing, nutrient film technique, kratky.
In soil, the ground does three jobs: it holds the plant up, it holds water, and it holds a reservoir of nutrients that the plant draws on slowly. Hydroponics removes the soil and makes you do all three deliberately — the plant is held in an inert medium, the water is supplied directly, and the nutrients are dissolved in it at a concentration you control. Nothing about it is mysterious and nothing about it is chemistry-set difficult. What it is, is unforgiving of neglect, because there is no buffer: a soil plant survives a forgotten week and a hydroponic plant in a small reservoir does not.
The reason the hobby is confusing to enter is that two very different versions share the name. One is a jar of basil or a tub of lettuce on a kitchen counter, costing under £30, needing no electricity at all, and producing food within about a month. The other is a tent with a controlled light cycle, extraction, a nutrient schedule and instruments, costing several hundred pounds and functioning as a small indoor farm.
Both are legitimate. The problem is that the second one supplies almost all of the writing, the video and the shop stock, so somebody who wanted the first buys equipment designed for the second, spends £250, harvests four pounds worth of lettuce and reasonably concludes the whole thing is a swindle. Work out which one you want before you buy anything, and the rest of this page is much simpler.
- What soil actually did
- Support, water and a nutrient buffer
- What you now supply
- All three, deliberately
- What it is good at
- Leafy crops and herbs, fast, all year
- What decides success
- Light, then consistency
Step 1: Pick a leafy crop, not a fruiting one
Lettuce, salad leaves, basil, mint, pak choi. They grow fast, they are cheap to fail with, they do not need pollinating, and they do not need the light intensity a tomato does. Starting with tomatoes or chillies is the commonest way to spend three months finding out your lighting was inadequate.
You will know it worked when: Something edible within four to six weeks.
Step 2: Solve light before anything else
A British windowsill between October and March supplies far less light than people assume, and light is the limiting factor in nearly every failed indoor grow. A modest LED panel on a timer transforms results more than any other single purchase. If you are not prepared to buy a light, grow in summer on the brightest sill you have and accept what you get.
You will know it worked when: The plant has enough energy to do anything at all.
Step 3: Build the simplest system that fits
A food-grade tub, a lid with holes, net pots and an inert medium. Add an air pump if you want deep water culture. Resist buying a multi-part system for a first attempt — everything you learn here transfers upward, and nothing you learn from an expensive system transfers down.
You will know it worked when: A working system for the price of a takeaway.
Step 4: Mix nutrient to the bottle, and buy a meter
Use a proper hydroponic nutrient — plants need more than nitrogen, phosphorus and potassium, and general houseplant feed leaves out what soil would have supplied. Follow the manufacturer’s dilution for your crop, because it is specific to their formulation. A combined pH and conductivity meter at £20–£60 is what turns guessing into observing, and calibrating it is a five-minute monthly job.
You will know it worked when: A solution you can measure rather than hope about.
Step 5: Change the solution on a schedule and keep a note
Weekly for a small reservoir, and write down what you did. Plants take up water and nutrients at different rates, so a reservoir left alone drifts in both concentration and pH. Four lines a week — level, pH, conductivity, what the plant looks like — is what turns the next problem into a diagnosis rather than a mystery.
You will know it worked when: You can tell what changed when something goes wrong.
The genuinely useful list, roughly in order of how much difference it makes:
- A light — The highest-impact purchase for indoor growing in Britain and the one most beginners skip. A modest LED panel on a timer is enough for leafy crops; fruiting plants want considerably more and this is where budgets escalate.
- A reservoir and net pots — A food-grade opaque container. Opaque matters — light on the solution grows algae, which is the commonest first problem in the hobby and is entirely preventable by not using a clear tub.
- An inert medium — Clay pebbles, rockwool or coco coir. It holds the plant and holds a little moisture; it supplies nothing. Which one is largely preference, and each behaves differently about water retention.
- Hydroponic nutrient — A complete formulation, usually sold as two or three parts to keep incompatible salts apart until dilution. Follow the maker’s figures; they are specific to their product and to the crop.
- A pH and conductivity meter — The instrument that makes the hobby legible. pH decides whether the plant can take up what is dissolved; conductivity tells you roughly how much is dissolved. Both drift, both are cheap to measure, and neither is guessable.
- An air pump, for active systems — Roots in still water run out of oxygen. This is the cheap component whose failure kills a crop fastest, so a spare is worth having.
- A timer — For the light and, in some systems, the pump. Consistency is most of what makes indoor growing work, and a timer supplies it for a few pounds.
- Go deeper — Choosing a grow light without wasting £200
- Work it out — Nutrient solution calculator
Hydroponic problems arrive faster than soil problems and are usually easier to diagnose, because there is far less to hide behind. Read each as symptom → likely class → what you can safely check → what to do next. Nothing here identifies a unique cause, and the honest use of it is to eliminate the cheap classes first.
- Green slime on everything — Light reaching the solution. Algae need light and nutrients, and you are supplying the second whatever you do. Check the reservoir for translucency and the lid for gaps. Opaque container, covered lid, and it stops. Harmless in small amounts, but it competes for oxygen and nutrients.
- Leggy, pale, stretched-out plants — Light, and almost always. The plant is reaching for more of it. Check how many hours it is getting and how far the light is from the leaves. This is the commonest complaint in indoor growing and it is almost never a nutrient problem, though it is very often treated as one.
- Brown, slimy roots and a smell — Oxygen, then temperature. Healthy roots are white and firm. Check the air pump is actually running and that the air stone is not blocked, then check the solution temperature — warm water holds less oxygen, and a reservoir sitting in the sun or next to a radiator is the usual culprit. This one moves fast, so act on the day.
- Growth stalled with no obvious cause — pH, most likely. Nutrients are only available to the plant within a pH band, so a solution can be full of everything the plant needs and deliver none of it. Measure rather than guess; this is what the meter is for. Adjust with proper pH-down or pH-up rather than household substitutes.
- Yellowing older leaves while new growth looks fine — Depletion. The plant is moving mobile nutrients from old leaves to new ones, which is what it does when the solution has run down. Check conductivity and how long since the last change. This is why a schedule beats topping up by eye.
- Fungus gnats — Damp medium and organic matter. Common with coco coir, less so with clay pebbles. Check for exposed damp medium at the surface and cover it. Annoying rather than serious, and far easier to prevent than to clear.
- The whole thing collapsed while you were away — The structural weakness of the hobby. Small reservoirs and active pumps mean no buffer: a pump failure, a power cut or a hot week can end a crop in a day. This is the honest trade against soil, and it is why a passive system is genuinely a better choice for somebody who travels.
Roughly the order things stop being the limiting factor:
- Light — The first ceiling and usually the only one that costs real money to raise. Almost every complaint about disappointing results is this.
- Consistency — Doing the weekly change on the week rather than when you remember. Unglamorous and the single biggest determinant of whether the hobby works.
- Measuring rather than guessing — The point at which the meter stops being an accessory. Once you are recording pH and conductivity, problems become diagnosable instead of mysterious.
- Harder crops — Tomatoes, chillies, strawberries. All need more light, more support and pollinating by hand indoors, and all are genuinely satisfying once the basics are automatic.
- Building your own — Where the technical-maker half of the hobby lives. Pumps, timers, float switches and — for a certain kind of person — a microcontroller logging the reservoir. This is the branch that never ends.
| System | How it works | Best for | The catch |
|---|---|---|---|
| Kratky (passive) | A sealed container of solution; the level falls as the plant drinks and an air gap forms around the roots | Lettuce, herbs, anything short-lived. The cheapest possible start | No top-ups mid-crop, so it suits fast crops only. Nothing rescues it if you get the starting level wrong |
| Deep water culture | Roots suspended in aerated solution, with an air pump running constantly | Leafy crops and a genuinely good first active system | A pump failure in warm weather can lose a crop in a day |
| Nutrient film technique | A thin film of solution flowing continuously down a shallow sloped channel | Salad at some scale, and the system that looks like the pictures | Very little water in the system, so any pump interruption is felt within hours |
| Ebb and flow | A tray of medium periodically flooded from a reservoir below and allowed to drain | Larger and fruiting plants, and mixed planting | More plumbing, more to go wrong, and the timing matters |
| Drip | Solution delivered to each plant through emitters | Big individual plants, and commercial-style growing | Emitters block. This is the maintenance job of the system |
| Wick | Passive capillary action drawing solution into the medium | Houseplants and very undemanding crops | Cannot supply a thirsty plant fast enough. Frequently disappointing |
The honest recommendation for a first attempt is a passive Kratky tub or a small deep water culture bucket, with lettuce or basil, under a light. It costs very little, it fails cheaply, and it teaches the two things that actually transfer: that light is the limiting factor almost every time, and that consistency beats sophistication.
- Still deciding — Hydroponics vs an allotment
Hydroponics has less maintenance than soil growing and far less tolerance for skipping it. There is no buffer: a soil bed forgives a forgotten fortnight and a twenty-litre reservoir does not. What follows is the whole routine, and it is short.
The weekly change, which is the core of it:
Step 1: Read and write down pH and conductivity before you touch anything
Take the readings from the old solution first. They tell you what the last week did — a rising conductivity means the plant drank faster than it ate, a falling one means the reverse — and that trend is the single most useful thing you will learn about your own setup. Four numbers a week is enough.
You will know it worked when: A record that turns the next problem into a diagnosis.
Step 2: Empty it, and look at the roots while you can see them
This is the only moment in the week you get a clear view. Healthy roots are white or cream and firm. Brown, slimy or smelling means oxygen or temperature, and catching it here is catching it days earlier than you otherwise would.
You will know it worked when: The best diagnostic in the hobby, for free.
Step 3: Rinse the reservoir and wipe the biofilm
A slick film builds on the walls whether or not you can see algae. Plain water and a cloth; no detergent, because residue is worse than the film. Every few changes, a more thorough clean.
You will know it worked when: A container that is not seeding the next batch.
Step 4: Mix fresh solution to the figures on your bottle
Water first, then nutrient, then check pH and adjust. Adding concentrate to an empty tank and topping up afterwards is how people get a locally strong mix that burns roots before it disperses.
You will know it worked when: A solution mixed the way the manufacturer intended.
Step 5: Top up with plain water between changes, not with nutrient
The plant drinks water faster than it takes up nutrients, so topping up with solution concentrates what is already there. Plain water between changes and a full change on the week is the whole discipline.
You will know it worked when: A concentration that does not drift upward all month.
The jobs that are not weekly:
- Calibrate the meters, monthly — pH and conductivity meters drift, and an uncalibrated meter is worse than no meter because you act on it. Calibration solution is a few pounds and the job takes five minutes.
- Clean or replace the air stone — Stones block with mineral deposit and biofilm, and the flow falls off gradually enough that nobody notices until the roots do. Cheap enough to keep a spare.
- Check the pump and its intake — Roots find pumps. In any active system the intake is the thing that blocks, and a pump that has been running dry is a pump that has been damaged.
- Strip and clean between crops — The one deep clean. Everything out, everything rinsed, net pots and medium cleaned or replaced. Reusing clay pebbles is fine and reusing them unwashed is how a root problem carries into the next crop.
- Check for light leaks whenever you change anything — Algae need light, and a lid that no longer seats properly after a rebuild is the commonest way it gets in.
One thing worth saying plainly, because it is the honest maintenance risk of the hobby rather than a chore: an active system left alone fails fast. A pump that stops on a warm Friday can cost a crop by Sunday. If you travel, that is an argument for a passive system with a large reservoir rather than for a better pump, and it is worth deciding before you build rather than after.
Hydroponic equipment is entirely legal to buy, own and use in the United Kingdom, and growing food crops indoors is an ordinary domestic activity that needs no permission from anybody. That is worth saying because the association with cannabis cultivation is real, is widely assumed, and makes people uneasy about a hobby that is in fact unremarkable.
What is illegal is cultivating cannabis, and it is illegal whether or not hydroponics is involved. This page covers growing food and ornamental plants and it publishes nothing about growing controlled substances. It gives no advice about concealing an installation, managing its heat or electrical signature, or anything else that would only matter to somebody doing it — not because the topic is embarrassing but because the only use for that material is committing an offence.
Two practical consequences worth knowing. Very large domestic electrical loads and heavily modified ventilation can attract attention, and a tenancy agreement or a mortgage condition may say something about alterations regardless of what you are growing. Both are worth checking before building anything permanent.
- Buying the tent version for the windowsill job — The defining mistake of this hobby and the reason so many systems end up in lofts. Decide which of the two activities you want before spending anything.
- Starting with tomatoes — A fruiting plant indoors needs far more light than a leafy one, plus support and hand pollination. Three months to find out your light was too weak.
- A clear reservoir — Light on the solution grows algae. An opaque container costs the same and prevents the commonest first problem entirely.
- Ordinary houseplant feed — Formulated on the assumption that soil is supplying the rest. In water, it is not, and the plant runs short of things nobody thinks about.
- Guessing instead of measuring — pH and conductivity are cheap to measure and impossible to eyeball, and stalled growth with no visible cause is nearly always one of them.
- Topping up instead of changing — Plants drink water and eat nutrients at different rates, so topping up concentrates what is left. A full change on a schedule avoids a slow drift into trouble.
- Expecting it to save money — It will not, at domestic scale, once the light is running. It is faster, cleaner, year-round and genuinely interesting, and none of those are cheapness.
- EC / conductivity
- Electrical conductivity, a proxy for how much dissolved salt is in the solution. It tells you roughly how strong the feed is, not what is in it.
- pH
- How acidic or alkaline the solution is. It decides whether the plant can take up what is dissolved, which is why growth stalls in a full reservoir.
- Kratky
- A passive method where the falling solution level leaves an air gap around the roots. No pump, no electricity, and the cheapest real hydroponics there is.
- DWC
- Deep water culture. Roots suspended in constantly aerated solution. The usual first active system.
- NFT
- Nutrient film technique. A thin flowing film of solution in a sloped channel. Efficient and unforgiving of pump failure.
- Net pot
- The slotted basket that holds the plant and its medium while letting roots out into the solution.
- Medium
- The inert stuff the roots sit in — clay pebbles, rockwool, coco coir. It supports and holds moisture and supplies no nutrition.
- Reservoir change
- Emptying and remixing the solution rather than topping it up. The core maintenance rhythm of the hobby.
- Will it save me money on food?
- No, not at domestic scale, and anybody promising otherwise is selling something. Once a grow light is running, the electricity alone generally exceeds the shop value of what a small system produces. What it does give you is herbs and salad that are genuinely fresher than anything you can buy, available in February, grown in a flat with no garden. Those are good reasons; saving money is not one.
- Do I need a grow light, or will a windowsill do?
- A bright windowsill will grow herbs and salad between about April and September in most of Britain. Outside that, no — winter daylight here is well below what even a lettuce wants, and light is the limiting factor in nearly every disappointing indoor grow. If you want the hobby to work all year, the light is the purchase to make first, ahead of any system upgrade.
- How much attention does it actually need?
- Ten minutes most days to look at it, and half an hour weekly to change the solution and check pH and conductivity. The important thing is not the total time but the absence of a buffer: soil forgives a missed fortnight and a small reservoir does not. If you travel often, a passive system with a large reservoir is a much better fit than an active one.
- What is the easiest thing to grow first?
- Lettuce or basil, in a passive tub, under a light. Both are fast, cheap, undemanding, need no pollination and give you something to eat inside about a month. Everything you learn from them transfers to harder crops, and failing at them costs a few pounds rather than a season.
- Is any of this illegal?
- No. Hydroponic equipment is legal to buy, own and use, and growing food indoors needs nobody’s permission. The association with cannabis cultivation is well known and it is worth being plain about: cultivating cannabis is an offence whether or not hydroponics is involved, this page is about food and ornamental plants, and it publishes nothing that would only be useful to somebody growing a controlled substance.
- Why does everything I read give different nutrient numbers?
- Because the right number genuinely depends on the product, the crop, its growth stage and what is already dissolved in your tap water — which varies enormously across Britain. Every manufacturer formulates around a different baseline. That is why this page publishes no figures at all: the correct ones are on the bottle you bought, and a general number would be wrong in most kitchens while looking authoritative.
If you like this
Each of these is here for a stated reason, not because it is also a hobby.
Similar to
- Bonsai — Indoor growing as a daily attentive practice rather than a seasonal one, where the plant responds to consistency and the interesting part is reading what it is telling you.
- Fishkeeping — Both are small managed water systems kept indoors, both are diagnosed with a pH meter and a habit of writing things down, and both punish neglect faster than the soil-and-air versions of the same interest.
Goes well with
- Composting — Opposite approaches to the same question of where a plant’s nutrition comes from — one builds soil, the other replaces it — and a grower who has done both understands what the ground was actually doing.
- Microcontroller projects — Reservoir levels, pump timing and light cycles are exactly the sort of thing people automate, and the technical-maker half of hydroponics runs straight into this.
Substantial
Last reviewed 2026-08-18. Cost, time and difficulty figures on this page are HobbyHQ estimates — see how we work. Something here wrong or out of date? Tell us.