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.

Saving herb seeds

Seeds from the Secret Garden's fennel plant against the sky.

The fennel plant in the Secret Garden is now over seven feet tall, throwing out aromatic feathery leaves, delicate flowerheads which then produce a multitude of pungent fennel seeds. This is a fennel plant (Foeniculum vulgare), grown as a herb rather than the variety grown for its bulbous root (Florence fennel or Foeniculum vulgare "Azoricum"). The leaf fronds are used for flavouring fish and salads, the flowers in pickles, and the seeds in spiced foods, stuffings, and sauces.

Herb fennel is a perennial plant. These impressive high stems will die back over the winter, but you'll usually see bushy feathery regrowth at the base of the main stalks starting in autumn which will come back strongly in spring. It is happiest in a light, well-drained soil in a sunny sheltered site.

Having successfully raised your herb plants they will eventually set seed if you leave the flowerheads on the plant.  Herbs like coriander, dill, lovage and fennel have edible seeds as well as leaves. In using the seed in the kitchen as well as the leaves - and also the flowers, see our post here - you will be getting maximum value from your plants. The seeds from your own herbs will also have an unmatched freshness and concentration of flavour.

Even if you don’t eat them, you can save the seeds to grow next year. This is one way to ensure that over the generations you will raise plants which is perfectly adapted for your conditions. 

Let the plant grow and flower, after which it will set seed. Cut the seedheads before they fall to the ground. You might want to put the whole seedhead in a paper bag and snip the stem to ensure no seed is wasted. 

Next, remove the chaff – the bits of stalk and seedcase. Put the seed in a jar and seal. Label it carefully. 

Store seed somewhere cool, dark and dry, and, for culinary use, try to eat them within three months. If you're saving the seed to sow again next year, keep them in a paper bag or envelope (not plastic or polythene), rather than  a jar, again somewhere cool and dark.

For detailed advice on saving seeds for a number of vegetable plants, the best place I've found on the web is Real Seeds which has detailed and authoritative advice.

A preservative worth its salt

Salting is one of the oldest methods of preserving food. It’s also convenient for the home cook as no specialist equipment is needed. Common salt is quite good enough to use as a preservative – the other commonly used is saltpetre (sodium nitrate plus potassium nitrate). 

Salting includes both dry salting, where the food is covered in salt, and brining, where the salt is dissolved in (most often) water and poured over the food. 

The way salting works as a preservative is by osmosis. You will remember osmosis from chemistry lessons at school – water will move through a semi-permeable membrane from a weak solution to a strong one. In their natural state, plants (ie, foodstuffs) contain salts and minerals in weak solution, in which bacteria live happily. The salt draws moisture from the foodstuff, drying it out slightly, and inhibiting the bacteria from reproducing.

Additonally, salting halts the action of enzymes which can contribute to the decay of foodstuffs. When you put sliced apple into brine or an acid solution like lemon juice to stop it from browning, this is using the brine or acid to stop enzyme activity. 

Foods that are commonly salted include fish: salt cod is practically national dish in some countries; cabbage, in the form of sauerkraut, and also the Korean dish kim chee; beef – Jewish salt beef, for example; and vegetables – think of the many tinned vegetables you buy that are preserved in salt.

Then there are the popular middle Eastern preserved lemons, which are simply salted lemons, and which you can easily make yourself. These are made best with small lemons which you can sometimes find in middle-Eastern stores; if not, you can use ‘normal’ sized lemons, or try preserving limes, or even satsumas instead, using the same method detailed here (updated from our post on citrus gifts, December 18^th, 2012.

Preserved lemons 

6 lemons 

Sea salt 

Give five of the lemons a quick wash and dry. Slice each lemon into four wedges but don’t cut right through the lemon – leave the wedges attached at the stem end. Rub the sea salt into the wedges and pack into a wide-necked, preferably sterilised, 1-litre jar. 

Put the kettle on. 

Sprinkle a tablespoon of salt over the lemons in the jar, then juice the last lemon and add this to the jar. Top up with boiling water, then seal the jar. Leave for a month before using. 

Unopened, these keep really well in a cool dark place. After opening, keep in the fridge.

Hanging on to herbs

Even the most well-stocked herb garden will be looking a little thin by this time of year. Well-established rosemary bushes, bay trees, and sage plants will have fresh leaves all year round, but mint will die down completely, marjoram will be looking rather woody by now, and parsley and oregano will be distinctly straggly.

Most herbs can be preserved for use when fresh leaves aren't available. These days we tend to think of dried herbs as an inferior substitute and it's true that some herbs keep better than others, but it's also the case that your properly dried herbs will be far superior to a jar of dusty leaves that has been hanging out at the back of the mini-mart for months, if not years.

Some herbs dry better than others: oregano, tarragon, and bay leaves all dry well and can be used in a variety of ways. Don't even try to dry basil leaves, and there are better ways to preserve parsley.
You should pick your herbs for drying with care. Find long branches with plenty of healthy leaves on them. Remove any brown or damaged leaves and check over for insects and mites. Wash and dry if necessary. Tie the stems together and wrap loosely in muslin or put them in large paper bag. Close the bag around the bottom of the stems and punch some air holes at the top of the bag.

Find somewhere warm, and well-ventilated without being draughty, where you can hang your herbs up. If you can’t hang them up, then lay them out singly with space around each stem on a tray 

Under the rafters in the loft, an airing cupboard, or a cupboard under the stairs are both good. I dry most things over the cooker hood 

Leave the herbs until completely dry, then transfer to a jar. Try not to break up the leaves – they will retina their flavour better if you crumble them just before you use them.  

Seal tightly and store in a cool, dark, cupboard. Try to use them within three months to get the best of their flavour.

Freezing herbs

What about those herbs that don't dry well? Parsley and basil are both reasonably good after freezing. You can freeze whole leaves in a bag, or in ice cube trays. In both cases, I'd say they are best used stirred into dishes such as casseroles, rather than in salads or as a garnish.
To freeze in a bag, pick out your best leaves or sprigs and lay them out in a single layer, not touching, on a tray. Place in the freezer and leave until frozen. Then transfer to a freezer bag and seal. 

To freeze in an ice cube, chop the herb finely, then squish into ice cube trays. Carefully fill the tray until the herbs are just covered. Freeze, then remove from the freezer and top up each cube with water – that way the chopped leaves won't all float up to the top of the cube and be exposed to the air. 

Once completely frozen, push the cubes out of the trays, transfer to a bag and replace in the freezer. 

Frozen herbs - by either method - should be used within three months. 

Herb vinegars

Thyme vinegar, left, and tarragon vinegar, steeping. The
vinegar will be strained and decanted before being
stored and used.

Herb vinegars make beautifully flavoured salad dressings. Tarragon vinegar is probably my favourite but rosemary or thyme vinegars are also intensely fragrant and will give your gravy a lovely sharp herby finish.

Again, pick leafy stems in prime condition. Bruise the leaves slightly, either by running the rolling pin over them or with a pestle. Put the herbs in a sterilised jar, cover with a plain vinegar (I usually use white wine vinegar, sometimes cider vinegar) and leave somewhere warm for 2-3 weeks, giving it a good shake every now and then. 

Strain the vinegar through a fine sieve or muslin into another sterilised bottle. Seal and use when required.  

Jams, jellies and chutneys

Smoking, drying and salting have all been used for hundred, indeed thousands, of years to preserve food. In the days before refrigeration and freezing, people relied on time-honoured methods for keeping food from spoiling.  Using sugar is necessarily a more modern technique, given that we only started importing sugar cane in the 16th century and the sugar content of beet wasn’t discovered until the 1700s. 

It was the Victorians and then Edwardians who took preserving with sugar and elevated it to high art in the kitchen. They filled their larders with jams, jellies, catsups (ie, what we now call ketchups), syrups, pickles, and chutneys, all of which use sugar to a greater or lesser extent for its preservative properties. 

These days, we don’t really have the storage space of the big Victorian and Edwardian houses. And for many of us, we don't have much in the way of spare time. With fridges and freezers, there simply isn't as great a need to find ways to keep food beyond its natural sell-by date.  Instead we can concentrate on using time-honoured preserving methods to deal with a glut of produce or to create something different (and often superior) to the usual commercially prepared jams and jellies. 
Both jams and jellies rely on sugar and pectin for taste, consistency and ability to keep well. Pectin is a carbohydrate found in the cell walls of fruits and vegetables. It is a natural setting agent and it is the presence of pectin that makes jams and jellies thicken and set. Fruit jellies do nor (or should not) contain gelatin; they ‘gel’ through the presence of pectin. 
Some plants are richer in pectin than others. Strawberries, for example, are notoriously low in pectin and often strawberry jam needs to be made with sugar that has had pectin added to it. Apples are high in pectin and are often added to low-pectin fruits as another way of helping them to set, as are another high-pectin fruit, redcurrants. Damsons, plums and quinces are naturally high in pectin and will thicken into jam or jelly relatively easily. 

Jams include whole or chunks of fruit. The liquor in which the fruit is suspended should be thick and syrupy, but not jellied. 

Jellies are strained and so contain no fruity lumps. A properly made jelly should be clear, not cloudy. Ideally a fruit jelly for spreading on toast or serving with meat should be less hard-set than a dessert jelly. 

The sugar added to jams and jellies acts as the preservative - without added sugar the fruit won't keep, nor of course will they taste so sweet. Sugar is currently public food enemy number one and there’s no doubt that we should probably all eat less of it . However, you can't significantly reduce the sugar content in a jam or jelly and maintain the same preservative effect. If the amount of sugar required makes your teeth itch, then by all means reduce the amount of sugar to your taste, but then store the preserve in the fridge and eat it all up within two weeks. 

Chutneys are derived from the Indian ‘chutni’, or ‘chatni’ (think of the ‘chat’ that you can eat in an Indian restaurant today), a spicy relish eaten as a side dish or accompaniment. Indian chatnis or relishes tend to be more spicy and savoury – and always vegetarian. When the British first encountered them in early Colonial days and brought them home and adapted them, it was the sweet and fruity aspect of chutneys they enjoyed. So our chutneys, as opposed to chutnis, tend to be sweeter, and less fiery - more of a cross between a jam and a pickle. Chutneys rely on both sugar and vinegar (and salt, to some extent) to preserve their ingredients.

General tips for making jams, jellies and chutneys

• Use copper, steel or aluminium pans for making sugar-based preserves. Enamel pans are fine so long as they are not chipped. 
• Use non-reactive, ie, not copper or aluminium, pans for vinegar-based pickles. 
• Pick or choose fruit that is exactly ripe. Overripe and your jam or jelly might ferment. Underripe and it will lack flavour and will need more sugar. 
• Don’t used the blemished parts of fruit. It will impair the flavour.  
• Don’t pick fruit when it’s wet. It will be waterlogged and your jam/jelly will be weaker in flavour, and might go mouldy. 
• Jams and jellies should be cooked until they are just set - test the liquid frequently to ensure that you don't overcook. Chutneys need to be cooked long and slow so that the ingredients soften and the flavours have plenty of time to blend.
• The jars you use to store the preserves in should be sterilised. This is not a complicated process. The easiest way to sterilise jars (and their lids) is to put them through a dishwasher cycle (not a low temperature, or economy setting) and then into an oven at 120 degrees to dry off.  Alternatively, you can wash, then rinse the jars in very hot water, and dry off in the oven as above.  
• You can sterilise in the microwave by filling jars half-full with water and heating on high for 2 minutes. Empty the jars and dry in the oven as above. 
• The jars should have properly fitting, airtight lids, which should also be sterilised in hot soapy water, rinsed and dried.  
• Your jams, jellies and chutneys should be stored in a cool, dry, dark place. Once opened, keep them in the fridge.  
• Chutneys should be stored for at least three months before eating, so that the flavours can blend and mellow properly.

I've been lucky enough to have a glut of quinces from the tree this year - nearly 200 hundred plump quinces each weighing around 300g or more. The blossom on quince trees doesn't appear until May, by which time the weather had warmed up and it stayed warm throughout the summer - perfect conditions for developing and setting plenty of fruit.

Quince jelly is a great way to may the most of quinces when they are plentiful. It's a simple jelly to make, it cooks to the most beautiful clear amber colour and the resulting jelly is delicious, whether spread on bread or toast, or eaten to accompany meats or cheese.
Furthermore, if you go on to make quince cheese (quince paste or 'membrillo') with the same quinces, you get two sweetstuffs for the price of one: the jelly from the juice and the membrillo from the pulp.

Quince jelly 

The first stage with any jelly is to extract the juice. We do this without any sugar added at this stage. Chop up the fruit. Don’t peel it or core it – the peel and pips contain lots of valuable pectin. Do remove any blemishes, stalk or leaves. Put the chopped pieces in a big non-reactive pan and add lemon juice and lemon zest – about one lemon for every 1.5kg or 3lbs of chopped fruit. 

Then add water: 2 litres for every 1.5kg of fruit, although here I tend to think in imperial measurements and add a pint of water for every pound of fruit. Bring this to the boil and simmer away for about an hour and a half. You can use a potato masher to push the fruit down in the water and make sure lots of flavour is released. At the end of an hour and a half, the fruit should be very soft and mushy. 

Next you need to strain the fruit juice. Traditionally people suspend a jellybag made with a muslin square over a bowl and let the juice drip through. You can buy special jelly bags and stands, but I still like the old-fashioned method of turning a chair upside down on top of another chair and tying a big colander to the upturned legs and draping my muslin over the colander. My mother-in-law rigs up something similar using the clothes horse - another traditional piece of equipment in its own right.

Whichever way you use, give your fruit mix several hours, preferably overnight, to strain, and don’t, whatever you do, try to speed the process up by pressing down on the colander. This will give you cloudy jelly. 

What you are left with after straining quinces is an opaque pink juice, which is used for making jelly, and the quince pulp, which can be used to make membrillo.
The next stage is to boil this juice up with sugar until it sets into a jelly, then pour it into sterilised jars. 

Start sterilising your jars by whichever method you favour. Get a cold plate and a teaspoon and place these near the hob on the worktop. Have a tea strainer, mesh spoon, or shallow spoon handy for skimming. Measure the amount of juice you have. For every 600ml of juice, you need 450g of sugar.
Pour the juice into a large pan and add the sugar. Stir over a low heat to dissolve the sugar, then turn the heat up to bring the juice up to the boil. From this point on, you need to keep a careful eye on the pan. The syrup should be maintained at a good rolling boil, so that it looks pale and almost foamy as it bubbles away. This is one process where a gentle simmer won't do. On the other hand, you don't want  it to bubble up so fast that it boils over.
When the liquid boils up, you'll see a white residue, like froth, or even something more solid, forming on the surface. This needs to be skimmed out of the jelly, either with a spoon, or a strainer. I find sweeping a tea strainer through the top of the liquid is an effective way to do it. 
How long you need to boil the syrup for will vary from batch to batch. I would usually expect around 20 minutes of good, hard boiling, but it could be less and is quite often longer. Test your liquid initially after about 5 minutes to get an idea of how it's progressing, but don't expect anything like a set at this stage.
To test manually, dip your teaspoon into the pan and drop a spoonful of the liquid on to the cold plate. Leave it to cool, then push your forefinger through the little pool of liquid on the plate. If it feels syrupy, if the surface of the liquid wrinkles at all as you push your finger through it, and if the the two sides of  the liquid stay separated instead of pooling together again after you have lifted your finger again, the your jelly is set and ready to pour into jars.
So, do your first 5 minute test, then test again after 5 minutes. This second test should look much more syrupy, but you probably won't get that tell-tale wrinkling of the surface of the liquid on the plate. From now on, it's a good idea to take your pan off the heat when you test. You don't want to find you've achieved your set with the pan still merrily bubbling away, as it carries on cooking your jelly. Once your liquid starts to look syrupy, test every 2-3 minutes. When you think it has set, let the bubbles in the pan die down and skim again so that you are left with a clear amber syrup. Have your warm sterilised jars ready and a ladle and, if you have one, a jam funnel (an ordinary funnel will be just as useful).
Spoon the syrup carefully into the jars and cover with the lids. Leave to cool, then tighten the lids fully. Label the jars and store somewhere cool and dark.

Quince cheese

Take the soft chunks of quince left over after straining for jelly, above, and push through a sieve, or, less arduously, a mouli-legumes. I find that if you use a mouli and start with the disc with the largest holes, then pass the puree you get from that through the smallest disc, you will get a fine quince puree for rather less elbow grease than trying to get the pulp through a sieve straightaway. Whichever method you use it's still hard labour. Don't be tempted to puree in the food processor, though, you want to sieve out the pips and skin and core, not pulverise them.

Weigh the final puree, put in a heavy-bottomed pan (a wide, non-stick pan is a Godsend), and add the same amount in weight in sugar. So, if you have 1kg of quince, add 1 kg sugar. Stir over a medium heat until the sugar dissolves, then bring to the boil - the puree will pop and bubble. It's rather like looking into the crater of an active volcano.

Keep stirring and keep the mixture on the boil. The colour will deepen from pale orange to a deep rich reddish-brown. The puree will thicken and eventually - it may take up to an hour - you will be able to draw your spoon along the bottom of the pan and the mixture will be stiff enough to stay separate in the pan. Remove from the heat.
You can store quince cheese in small wide-topped pots, or spread out on greaseproof paper to cut into shapes when it's cool and fully set. If using pots, dampen a piece of kitchen paper with a little vegetable oil and rub it around the base and sides. This will make it much easier to unmould the cheese later. I use the little plastic pots which the local Chinese takeaway uses for your dipping sauces - they're just the right size and shape.
Leave to cool completely, then store somewhere cool and dark or in the fridge. Quince cheese seems to keep forever.