Hydroponics explained (and what works best)

perlite in a steel scoop

The Technique

At its most basic, hydroponics is growing plants using only nutrients, water and some kind of growing medium. Rather than soil, fans of hydroponics use neutral materials like perlite (made from volcanic rock), vermiculite (a silicate), gravel and coco coir as the media for plant growth. The whole of the media is kept moist, but only the bottom 20% or so of the container is solely liquid. The damp upper 80% allows for effective drainage and good aeration whilst keeping the growing plants in place.

If you haven’t read it yet, I would suggest starting out with our Hydroponics for Beginners article.

Types of Hydroponic Media

Perlite 

Perlite an amorphous volcanic glass which is rich in silicon. You know those little white foam balls that you sometimes find in potting mix? The chances are that they are actually tiny pieces of perlite. 

Chunks of perlite are crushed and then heated. Heating expands the particles in the perlite until it ‘pops’, just like popcorn,  to become a white, porous rock. The tiny bubbles that form as part of this heating process hold the water and air that is so important to hydroponic gardening. Perlite maintains its structure through repeated soakings and so can be used again and again.

Perlite gives great drainage and good aeration whilst also holding water in its many tiny cavities. If you’re serious about trying hydroponic gardening then you’ll going to experiement with perlite. You can check out brands, mixes and pricing here or anywhere that sells hydroponic supplies.

Vermiculite

Vermiculite is a silicate which looks a bit like mica. 

Exfoliated perlite and vermiculite on white background

It is heated until it expands. The end result is a rough, pebble-like granule. These granules are divided into 4 different grades which each one better suited to a particular type of gardening.

Vermicule acts rather like a sponge, absorbing water and holding it. However, it breaks down over time, meaning you can’t reuse it endlessly.

Vermicule has superior water retention than perlite, but doesn’t hold as much air.

Gravel

Gravel has the advantage of being cheap and easy to find.

It is good at getting air to the roots, but doesn’t have the porous structure necessary to retain water and so drains quickly. This means that roots may dry out if you don’t keep pumping liquid through it. 

Although it can be reused, gravel is heavy.

Rockwool/ Stonewool/ Growool

Rockwool is made from rock which is heated to high temperatures and then turned into fibrous growing cubes and slabs. It looks rather like insulation (and is used as fire and soundproofing insulation).

rockwell cubes for hydroponic gardening

Its fibrous structure means that rockwool can hold both air and water in sufficient ratios to grow plants and it is gaining rapid popularity with home hydroponic growers and gaining shelf space in hydroponic supplies stores.

Clay Pebbles/ Grow Rocks

Clay pebbles are clay pellets which have been baked in a kiln. Sometimes called ‘grow rocks’ these pellets are packed with tiny air bubbles which means they are great for drainage. However, that also means that they aren’t so good at retaining water, unfortunately.

Heat expanded clay pebbles used as a growing media in hydroponics

Clay pebbles can be quite expensive to buy, but again, they are reusable after a good clean.

Coconut Coir

Coconot coir is sometimes called coconut fibre, this is the crushed husks of coconuts.

A piece of Coconut Coir used as growing medium in hydroponics

It is ‘organic’ and has the added brownie points of being environmentally friendly. In fact, coconut fibre is a by-product of coconut farming and using it for your hydroponic system turns it from a waste product into a commodity.

Coconut coir comes in a number of different grades and has good water and oxygen retaining properties. This, combined with its availability and environmental credentials, means it is rapidly becoming the medium of choice for many hydroponic gardeners and farmers.

Which Media Is Best?

What are you growing?

It might like an obvious question, but the answer makes all the difference to the type of media you use for your hydroponic set up.

If you are gardening in a wet climate or you want to lighten a clay-based soil then perlite is perfect as it is great for drainage and aeration. However, if you are trying to germinate seeds and are worried about them drying out, then vermiculite is the better medium as it is better at holding water.

As with so many things in life, a mix of media is often needed for optimum results and you may need to experiment a bit with various combinations until you find the perfect balance for your unique growing situation.

The Nutrient

The nutrients used in hydroponic systems are made commercially and can be bought almost anywhere that offers gardening supplies – from big hardware chains to specialised hydroponic supplies stores. Or even Amazon, which has come from a long way back to have a decent selection of suppliers.

And most hydroponic nutrients are very easy to apply. You simply dissolve a few grams or millilitres of the nutrient in water and add it to your hydroponic set up.

Interestingly, most of the hydroponic nutrients sold are pretty generic with little attention given to the needs of particular types of plant. Indeed, many hydroponic growers not only use the same nutrients for a variety of different crops, but also make no attempt to replace any specific nutrients that many have been absorbed more than others when nurturing a specific plant. This is sub-optimal.

The nutrient is added regularly to the hydroponic system and the fun part is working out exactly how much of each ingredient that makes up your nutrient solution is being used by particular plants at varying stages of their development. How often you need to top up the solution may depend on such variables as how salty or chalky your water is and how quickly it evaporates.

And whilst the instructions that come with nutrient bottles are a good place to start, as with so many things in life, you might find it best to experiment a bit with different concentrates and rates of watering yourself to find that sweet spot.

The Location

So where should you set up your hydroponic system?

Put it in exactly the same spot as you would if you were popping the plant in the ground. Generally, a warm, sunny place where you can keep an eye on it.

Sowing

If you want to grow from seeds, fine grade (Number 1) vermiculite is the best media. Its sponge like qualities make it perfect for holding water and nurturing seeds. Even crops like carrots can be started off in a few centimetres of vermiculite and if you lay it on top of some perlite, the carrots can stay where they are and grow to maturity without you having to transplant them once they have sprouted.

If growing seeds from scratch is daunting, go for commercially grown seedlings instead. Once you get them home, rinse off the soil that they came in and soak them in some diluted hydroponic nutrient solution until they are plump and turgid. Then remove them from the solution and plant them in your hydroponic structure. The soaking stage should ensure that they ‘take’ straight away.

And a quick word on herbs. If you plan to grow herbs, start with a diluted solution. Many herbs have a masochistic streak and grow best in comparatively harsh environments and with minimal nutrients.

Infographic Hydroponic Illustration

The Hydroponic Advantage

Growing plants hydroponically gives gardeners a level of control that many find both reassuring and rewarding. 

It can be done in limited space and with the right set up you can grow a range of crops that would struggle to survive in a regular vegetable plot. And you can raise veggies all year round too, if you wish.

No soil means no soil-borne diseases or pests. It also means no digging or weeding and no need to companion plant or crop rotate to put nutrients back into the ground.

It is perfect for the gardener who wants maximum return from as little effort as possible (me!), or the gardener who isn’t as fit or mobile as they’d like to be or has little time to spare maintaining soil quality and keeping parasites at bay.

And whilst fans of all things organic may claim that ‘artificially grown’ hydroponic veggies don’t taste as good, the truth is they’d be hard pushed to spot the difference. Hydroponic produce is fresh, glowing with health and has no chemical taste from the nutrient solution.

With hydroponics, for a little bit of research and outlay, the returns can be huge. But for most of us, it’s fun, its interesting and it feels great to produce fabulous fruit and vegetables. And I personally love experimenting with a technique that has been around since the Hanging Gardens of Babylon!

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