Complete guide to hydroponics

Advice on growing plants hydroponically, and how to get started.

What is hydroponics?

Growing plants without soil is known as hydroponics or hydroculture. It involves growing plants either in an inert medium such as rockwool and drip-fed water and nutrients, or simply 'planting' them direct in the nutrient solution. At the most basic level, an example of a hydroponics is a hyacinth vase, which is designed so the hyacinth bulb sits above the water and the roots grow into it. Hydroponics systems are ideal for using indoors or outside, for any type of plant. Growing hydroponically is particularly useful for small spaces where access is awkward for traditional, bulky, and heavy potting composts, and for living walls and roof gardens, or growing indoors with minimal mess.

Commercial crops produced hydroponically include tomatoes, cucumbers, salads and strawberries. These are grown in glasshouses and polythene tunnels, as well as under cover with natural light replaced by LED grow lights, including as futuristic space-saving ‘vertical farms’. Some of the large-scale ‘living wall’ installations seen in public buildings are growing hydroponically. Commercially, hydroponics is also known as Nutrient Film Technique (NFT), where the solution constantly recirculates to supply the roots with oxygen as well as water and nutrients.

What is aquaponics?

The technique of aquaponics takes raising food a step further, combining growing plants along with raising fish. Instead of buying and supplying plants with fertiliser, they take up the nutrient-rich waste produced by the fish. Commercial operations raise fish such as rainbow trout by this method, and domestic-scale kits are available, too.

How do hydroponic systems work?

Hydroponic systems use a water and nutrient solution instead of soil, often in conjunction with an inert growing medium such as rockwool. They're designed for multiple plants – anything from three, to dozens or even hundreds. Plants are supported either in an inert growing medium such as clay granules, perlite or rockwool, or (less often) in shaped trays or containers to hold plants above the water level. Many of our most popular vegetable crops are commercially grown hydroponically – for example tomatoes are grown in rockwool and drip fed water and nutrients.

The main nutrients plants need for healthy growth are nitrogen (N), phosphorus (P) and potassium (K). Different NPK ratios are fed to plants depending on whether or not they produce fruit, and what stage of growth they are at. Nutrient solutions also contain specific quantities of magnesium, calcium and sulphur, along with tiny amounts of trace elements such as copper, boron, iron, manganese, molybdenum and zinc. As the plant roots absorb the water the nutrients can become more concentrated, which can damage the plants. Nutrient solutions may therefore need to be topped up, and should be replaced around every two weeks. The pH of the solution is also a consideration, and is usually kept at between 5.8 and 6.2.

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Because plant roots must have oxygen as well as water and nutrients, it's necessary to either manually add fresh nutrient solution regularly or have a pump that circulates and recycles it. A variant of this is an ebb and flow system, where the plant containers (filled with rooting media) are stood in a trough or basin that is periodically flooded with nutrient solution, which is then allowed to drain back to a stock tank.

Benefits of hydroponics

• Clean growing method that avoids the bulk, weight, and mess of soil or potting compost
• Suitable for small-scale growing indoors or outside
• Vertical, tiered systems make the most of limited space
• Growth is often faster and stronger than traditional growing due to little or no pest or disease issues, and no weeds
• Competition from other plants is reduced, as plants are grown in separate modules
• Hydroponic systems are more portable than soil-grown plants, so are ideal for renters

Disadvantages of hydroponics

• Initial equipment cost can be high
• Only produces small amounts of food in comparison to cost and size of setup
• Systems need regular monitoring and input – even fully automatic ones need care
• Containers and systems require regular cleaning to avoid buildup of algae

How to have a hydroponic garden

A variety of home hydroponics kits are available online, with step-by-step instructions on how to keep your plants healthy.

If you want to make your own garden hydroponic system, there are several options. At the smallest and most basic level, you can make your own hydroponic pots from 2-litre plastic bottles, by cutting off the top half and inverting it inside the lower half, with a piece of capillary matting over the cap hole to draw up moisture. Add your nutrient solution to the bottom of the bottle and place your plant in the inverted top, so its roots sit in the nutrient solution.

You can also make a simple hydroponics system using ordinary house guttering. Fix sections of gutter to a wall or fence, each one slightly higher at one end than the other, so the water/nutrient solution drains from the top one down.

Advice on buying hydroponic planters, pots, and systems

• Ready-made hydroponics systems come in a wide selection of sizes, designed for ornamental house plants or productive veg-growing
• Consider the amount of regular maintenance involved and what you have time for – automatic systems are easiest to manage
• Consider whether you want to grow plants directly in a nutrient solution or in an inert growing medium such as rockwool or clay pebbles

Where to buy hydroponics systems

Best hydroponic crops to grow

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Small and short-lived plants are best for growing hydroponically, resulting in good crops in a relatively short time. Root crops, along with large, long-lived plants such as woody shrubs and trees, aren’t suitable for hydroponics.

1. Courgettes – vigorous, bushy plants produce a good crop in summer. Courgettes must be picked frequently, when small, otherwise they grow into marrows. Frost tender
2. Dwarf French beans – neat bushy plants produce long, slender, green or yellow beans. Frost tender
3. Herbs – small, tender herbs like parsley, basil, coriander, dill, mint, and chives are ideal for hydroponic growing. Some herbs are short-lived and need replacing every two to three months, while others, like chives and mint, are hardy and perennial. Pick little and often to boost fresh growth
4. Kale – leafy green kale or 'Cavalo Nero' produce nutritious leafy growth to pick at any stage of growth
5. Salad leaves – mixed salad seeds give the quickest harvests of fresh, tender salad leaves, potentially for most of the year. Sow successionally every six to eight weeks through the growing season to ensure a regular supply
6. Tomatoes – bush and trailing varieties are best in a limited space, with growth that spreads over the containers, bearing juicy and delicious fruits in summer and early autumn. Tall-growing ‘cordon’ tomatoes need regular training and grow to at least 1.5 metres high. Frost tender
7. Strawberries – neat bushy plants are ideal for hydroponic growing, with sweet-tasting summer fruits that taste far better when picked and eaten fresh compared to shop-bought crops. Hardy and should crop for several years
8. Watercress – ideal for hydroponic growing, producing leafy shoots packed with nutrients that can be picked regularly through the year