Hydroponic gardening is growing plants without soil, in water that carries the nutrients the plant needs. The roots sit in water, or in an inert material such as clay pebbles, perlite or rockwool, and a nutrient solution feeds them directly. It sounds futuristic, and in some ways it is, but the idea is old: plants do not need soil, they need water, nutrients, light, air and support, and hydroponics supplies those without soil. This guide explains how hydroponics works, the main systems in general terms, what grows well, and — honestly — what it costs, what can go wrong, and whether it is right for you.
The appeal is real. Hydroponic plants can grow fast, because they do not have to search through soil for food and water. They can be grown indoors, all year round, in a small space, with no weeds and fewer soil-borne pests and diseases. They use water efficiently, because the water is recirculated rather than draining away. And they can be grown where there is no soil at all — a flat, a garage, a greenhouse, a classroom. But hydroponics is not a shortcut to free food. It needs equipment, electricity, monitoring and maintenance, and when something goes wrong — a pump fails, the nutrient solution goes wrong, the power goes off — plants can die quickly, because they have no soil to buffer them.
How hydroponics works
A plant needs water, nutrients, light, air and support. In soil, the soil provides water, nutrients and support, and the gardener adds the rest. In hydroponics, the grower provides all of them: a nutrient solution supplies water and minerals, a light — the sun, or a grow light indoors — supplies light, air is supplied to the roots by the design of the system, and an inert material or a frame supports the plant. The nutrient solution is the heart of the system: it is water with mineral salts dissolved in it, mixed to a recipe for the plants being grown, and it must be kept at the right strength and the right acidity, or the plants will suffer.
The roots need oxygen as well as water and nutrients. In a system where roots sit in water all the time, the water must be aerated, or the roots will suffocate and rot. In a system where roots are misted or flooded and drained, the air reaches them between waterings. Getting the balance of water, air and nutrients right is the skill of hydroponics, and it is why monitoring matters: a soil garden forgives a mistake for days, while a hydroponic garden may not forgive it for hours. If you are unsure about hydroponics in your area, check your local extension service for advice.
The main systems, in general terms
There are several common hydroponic systems, and they differ mainly in how the nutrient solution reaches the roots. In a deep water culture system, the plant's roots hang in a reservoir of aerated nutrient solution, with an air pump bubbling air through it. It is simple and cheap to build, but if the pump fails, the roots can suffocate quickly. In a nutrient film system, a thin film of nutrient solution flows continuously over the roots in a channel, and the roots are exposed to air above the film. It suits leafy crops, but it needs a reliable pump and a level channel. In an ebb and flow system, the growing tray is flooded with nutrient solution at intervals and then drained, so the roots get water and then air. It is flexible and suits many crops, but it needs a timer and a pump. In a drip system, nutrient solution is dripped onto the base of each plant, and the excess drains back to the reservoir. It is simple and reliable, and it suits larger plants such as tomatoes. In a wick system, a wick draws nutrient solution up from a reservoir to the growing medium by capillary action, with no pump at all. It is the simplest system, but it suits only small, light-feeding plants, because the wick cannot deliver enough solution for a hungry crop. In aeroponics, the roots hang in air and are misted with nutrient solution at intervals. It is efficient and fast, but it is the most technical system, and a pump failure can kill plants quickly.
No system is best for everyone. A beginner should start with a simple system — deep water culture or a drip system — with one crop, and learn how it behaves before investing in a larger or more complex setup. Do not buy an expensive system before you know whether you enjoy the monitoring and maintenance, because hydroponics is a hobby that rewards attention and punishes neglect.
What grows well hydroponically
Leafy crops grow best hydroponically: lettuce, spinach, chard, kale, herbs such as basil, parsley, mint and coriander, and other fast-growing leaves. They are light feeders, they grow fast, and they suit the small systems most beginners start with. Our growing lettuce, growing spinach and growing basil guides cover the crops, though they are written for soil growing — the plant's needs for light and temperature are the same, even if the feeding is different. Fruiting crops such as tomatoes, peppers, cucumbers and strawberries can grow hydroponically and can be very productive, but they need a larger system, more support, more food, and hand pollination indoors, because there are no bees. Our growing tomatoes guide covers the plant. Root crops such as carrots and potatoes do not suit hydroponics, because they need a medium to grow in and shape themselves against, and most hydroponic systems cannot give them that. Large plants such as fruit trees and shrubs are not hydroponic crops for a home grower.
Light, temperature and nutrients
Light is the limiting factor for indoor hydroponics. A sunny windowsill is rarely enough for strong growth, especially in winter, and most indoor hydroponic growers use a grow light. A simple LED grow light, hung close above the plants and left on for 12 to 14 hours a day, is the usual setup. The grow light calculator will help you work out hours and hanging distance. Temperature matters too: most hydroponic crops like ordinary room temperature, and the nutrient solution should not get too warm, because warm water holds less oxygen and encourages disease. Keep the reservoir out of direct sun, and keep the growing area ventilated, because still, damp air encourages disease.
Nutrients are the part beginners find hardest. The solution must be mixed to the right strength for the crop, and the acidity — the pH — must be in the right range for the plants to take up the nutrients. A solution that is too strong burns roots; a solution that is too weak starves the plants; a solution at the wrong pH locks nutrients away so the plants cannot use them, even though they are present. Buy a nutrient mix made for hydroponics, follow the instructions, and check the solution regularly with a simple meter or test kit. Change the solution regularly, rather than just topping it up, because topping up lets salts build up and the balance drift. Do not guess at nutrient recipes, and do not use soil fertiliser in a hydroponic system — it is not made for it, and it can damage the system and the plants.
Maintenance and what can go wrong
Hydroponics needs regular maintenance: check the pump and air supply daily, check the water level, check the nutrient strength and pH, look at the roots for signs of rot, clean the system between crops, and keep algae out of the reservoir by keeping it dark and covered. Algae grows where light reaches nutrient solution, and it competes with the plants and clogs the system. Root rot is the most common serious problem: roots turn brown and slimy, the plant wilts even though it has water, and it dies. It is caused by warm water, low oxygen, or disease, and it is hard to cure once it has taken hold — prevention, through aeration, cool water and clean equipment, is far better. A pump failure or a power cut can kill plants in hours, because they have no soil to fall back on, so a backup plan — a spare pump, a battery air pump, or simply checking the system daily — is worth having.
Pros and cons of hydroponics
The advantages are fast growth, year-round growing indoors, no soil and no weeds, fewer soil-borne pests and diseases, efficient water use, and the ability to grow where there is no soil. The disadvantages are cost, electricity, monitoring and maintenance, the risk of rapid failure if a pump or power supply fails, and the learning curve: hydroponics is a technical hobby, and it rewards a grower who enjoys measuring, checking and adjusting. It is not cheaper than soil growing for most home gardeners, once equipment, electricity and nutrients are counted, and it is not less work — it is different work. Be honest with yourself about whether you will enjoy that work before you invest.
Common mistakes
The most common mistake is starting too big, with an expensive system and many crops, before learning how one simple system behaves. The second is not monitoring the nutrient solution, so it drifts too strong, too weak or to the wrong pH. The third is letting the reservoir get warm or letting light into it, so algae grows and roots rot. The fourth is not aerating the roots, so they suffocate. The fifth is growing the wrong crops — root crops and large plants that do not suit the system. The sixth is assuming hydroponics means no pests or disease: it means fewer soil-borne problems, but aphids, whitefly and disease can still arrive indoors. And the seventh is having no backup for a pump failure or power cut. If you are unsure about hydroponics for your home, check your local extension service for advice.
Frequently asked questions
Is hydroponic gardening hard?
It is more technical than soil gardening, but a simple system with one leafy crop is a reasonable place to start. The work is monitoring and maintenance — checking the pump, the water level, the nutrient strength and the pH — rather than digging and weeding. Start small and learn the system before scaling up.
What is the easiest hydroponic system for a beginner?
Deep water culture or a drip system, with a leafy crop such as lettuce or basil. Both are simple, cheap to build, and forgiving compared with more technical systems. A wick system is the simplest of all, but it suits only small, light-feeding plants.
What grows best hydroponically?
Leafy crops: lettuce, spinach, chard, kale and herbs such as basil, parsley and mint. Fruiting crops such as tomatoes, peppers and strawberries can grow well too, but they need a larger system, more support and hand pollination indoors. Root crops do not suit hydroponics.
Do hydroponic plants need sunlight?
They need light, which can be sunlight or a grow light. Indoors, a grow light for 12 to 14 hours a day is the usual setup, because a windowsill is rarely bright enough, especially in winter. Keep the light close above the plants.
Is hydroponics cheaper than soil gardening?
Usually not for a home grower, once equipment, electricity, nutrients and monitoring are counted. Hydroponics can be faster and more productive per square metre, and it can grow food where there is no soil, but it is not a cheap shortcut to free food.