Hydroponics - growing without soil

Growing plants hydroponically, or without soil, is a clean, and resource-efficient way to successfully raise a variety of produce. While it has only become an established way to grow vegetables on a commercial scale in recent years, it's not a particularly new invention. The Hanging Gardens of Babylon are reputed to have used hydroponic growing techniques as were the floating gardens of Aztec Mexico. It's been used on Pacific Islands with no topsoil .  Closer to home, the philosopher/scientist and parliamentarian Francis Bacon – the one who some people suppose may have written some of the plays attributed to Shakespeare – wrote about soilless planting, and called it 'water culture'.

Conventionally, plants are grown in soil, typically made up of minute rock particles, organic matter (material which was once living, now decayed) and water. The chemical nutrients in soil, dissolved in the water, feed the plants and enable them to grow. The purpose of the soil itself, rather than the water in the soil, is to act as an anchor for the plant's roots, keeping it stable. So long as you provide the same liquid nutrients in such a way that the plant's roots can take them up, and you also give your plants something to hold the roots in, you don’t need the soil itself.

There are advantages to eliminating soil. Soil is messy stuff for one thing, and for another there is always an element of guesswork in using soil. It's difficult to know precisely, how rich, how chemically balanced, how fertile a soil is. If you have no garden, or are restricted to a patio or courtyard, or maybe have no outdoor space at all, you may not want to be lugging bags of compost through the house. Soil can also be contaminated, by toxic metals, or more mundanely, by pests or harmful fungi living in it. In this last case, you may not wish to grow edible foods in such an environment.

In a hydroponic set-up, you need a container for your plants, plus a growing medium which will be an inert material such as Perlite, Vermiculite, or rockwool (available from most garden centres), all three of which are rock-based, and highly water-absorbent. You can float your roots in water so long as the main stem has a collar, or block, to stabilise the plant. You will need to provide your plants with warmth, light and nutrients.

If you look around on the Internet you'll find off-puttingly long lists of technical equipment required for a hydroponic set-up: pumps, filters, hoses, lights, heat lamps, etc. You would be forgiven for thinking it's less like growing plants and more like a laboratory experiment.

However, much of this expensive and hi-tech kit is needed for hydroponic growing on an industrial or commercial scale. To successfully grow salad leaves an herbs on a windowsill, some pots, water and a soil-less growing medium is all you really need. And your liquid nutrients, of course. I tend to stick my hydroponic pots in a south-facing window and let them make the most of the natural warmth and light from that, but then I'm growing mostly herbs and salads which are less fussy than some plants.

Many of the salad leaves sold in supermarkets are grown hydroponically, as are what they call salad vegetables: tomatoes, peppers and cucumbers. If you’ve ever wondered how tomatoes can be labelled as UK grown and sold at this time of year, it’s because they are grown indoors, hydroponically. You may have heard of Thanet Earth, which is a site of four massive greenhouses covering over 200 acres, which grows solely tomatoes, cucumbers and peppers, all grown without soil, and all for distribution into supermarkets in the south-east. For Thanet Earth, being able to precisely control the environment means they can harvest tomatoes 52 weeks a year, cucumbers from February to November, and peppers from March to November. With no soil-borne diseases to worry about, Thanet Earth aims to use no pesticides at all – they do use biological controls, ie, introducing predators to deal with any pests.

Hydroponic cultivation has its opponents. The development of Thanet Earth was covered in the Daily Mail and included a quote from Jeanette Longfield of the food campaign group Sustain, who said: 'What are they going to taste like if they are grown in water rather than soil? … This is about producing bland food’.

The argument here is about what the French call 'terroir', when referring to growing grapes for wine: the complete environment that the plants are grown in, including the microclimate, the soil, and terrain. If the idea of terroir can give grapes their own individual characteristics, then logically it can also apply to fruit and veg. That while we calibrate liquid nutrient solutions and precisely control the climate (heat, light and water) for hydroponic crops, there may be trace elements or micro-minerals present in soil that we are overlooking in the hydroponic environment. I don’t know the definitive answer to the taste question. If you follow the terroir argument through, then a hydroponic crop should be very 'pure' tasting, with little or no deviation from one growing location to another. And there should be no bad years.

Pak choi plants growing in a hydroponic trough on the windowsill.

In this age too where organic growing is seen as 'better' than intensive farming - and hydroponic growing is pretty intensive, hydroponic cultivation can be seen as a step backwards.

What an organic philosophy and hydroponic growing have in common is the desire for sustainability. Both methods are far less fuel-intensive than using manufactured fertilisers. Organic systems aim to reduce soil erosion and exhaustion with the addition of organic matter; in many hydroponic systems, the growing medium can be reused many times. For example, perlite, the rock granules which are often used to anchor the roots, can be sterilised in a microwave and then used again for the next batch of hydroponically-grown seedlings. Thanet Earth exports electricity to the neighbouring area and recycles all its water. The micro-management that delivers precisely the nutrients needed to the growing plants also means there is far less waste.

Hydroponics - the good news ...
+ Sustainable
+ Efficient use of resources - less waste
+ Takes up relatively little space, with high yields
+ Versatile – does not need fertile soil, can be grown anywhere
+ Cleaner to maintain

... and the not-so-good
- Cannot be called organic
- Lot of management required to get the balance right
- Leaching if not managed properly
- Only suitable for some plants
- Concerns that soil-grown vegetable taste better

Hydroponic growing is ideal if you don’t have a garden, or you are restricted to pot-growing. The lack of soil makes it less messy for a start; the use of a precise set of nutrients administered at regular intervals takes a lot of the guesswork out of growing.

Where to buy
We used a simple base kit, costing £32.50 from The Achiltibuie Garden. Based in the north-west highlands of Scotland, this company specialises in developing hydroponic growing systems for domestic use. Many of their systems are modular, so that you can add extra units to the base kit if your needs increase. This windowsill kit shown below, is good for raising salad cut-and-come-again leaves and herbs.

The acorn pot in the top photo is suitable for growing chillies and also tomatoes, and also comes from the Achiltibuie Garden, costing £45.00 for a pack of three pots, plus a Perlite-based growing medium, mini-propagator, sample seeds and a generous supply of liquid nutrients.

Closer to the Secret Garden Club is Growell Hydroponics in Neasden, just off the North Circular in Brent Park and with branches throughout England, in Merton, south London, Birmingham, Bristol and Sheffield, among other places. They sell everything from nutrient mixes to complete irrigation, lighting and tenting systems for indoor growing.