Hydroponics For Lazy Buggers

We've discovered hydroponics, and haven't looked back. It's very simple to do, there are no weeds, there is no digging, plants grow really fast, and you can usually manage to have your plants at waist height. All the better to inspect your bumper crop.

Our hydroponic garden The best way to start is to use a fountain pump in a 20 litre bucket to circulate nutrient solution around some growing beds. The nutrient solution is purchased from hydroponic shops and is very cheap stuff. It comes as crystals A and B which you make up according to directions on the packet (mix up and add 5ml of each per litre changed every week, less often in winter). Do not use single mix stuff; it doesn't work whatever they say on the packet.

So pump goes in bucket (keep it way from your sleeping area as the pumps make some noise), pipe goes out into garden, and a bigger pipe comes back to the bucket. A little waterfall on the way back into the bucket keeps the water oxygenated. We use black plastic 14mm irrigation pipe (some call it 13mm) out from the pump and progressively reduce the diameter to 6mm and then 4mm (sometimes even 2mm) as it gets closer to the hydroponic beds.

Taps and tubing diameter are used to regulate flow rates to just under 1 litre a minute per bed. This is measured with such high-tech equipment as a jug and stopwatch. Lets see just what goes into the system:

Your Pump

Probably the most expensive bit you'll every buy for your hydroponics, but it should last for years - ask. Make sure it can pump at least 1 litre a minute per growing bed up to a height equivalent to the difference between the bottom of your bucket and the top of your highest bed. Make sure it has a practical attachment point for your piping - I put on a T-shaped adaptor and take 2 x 14mm tubes off mine.

Tubing

For the piping out of the pump on systems with less than 100 or so plants, use 14mm, 6mm, 4mm and 2mm tubing usually used for cheap irrigation kits. All tubing for hydroponic purposes must be opaque to light or algae will clog your system. As the system gets bigger, use PVC waterpipe: metallic fittings will dissolve in the nutrient solution, contaminating it and you.

For the return path use bigger tubing, as the returning fluid will not be under pressure. For low flow rates, 14mm tubing or opaque garden hose is suitable. For heavier flows, use conventional 20mm or even 25mm PVC piping, or branch rapidly to multiple 14mm pipes.

Hydroponic Channels

We make our hydroponic channels from 2m lengths of PVC rectangular section (50mmx100mm) downpipe. We chose 2m because that's the longest bits we can fit in the car; you can make them longer and save money on endcaps.

Holes are cut in the pipe to accept our little plastic pots. These holes are cut with one of those cheap sawblade rotary cutter things. I'd recommend the more solid holecutters, and wish I'd bought one instead of the cheap, round
sawblade things.

At the top end of the channel, drill the centre of the first hole about 10cm from the end. This allows for a little strengthening, the endcap and and for the water to spread from the inlet pipe. Now for the rest of the holes.

For large crops like big lettuce, chillis and brassica we'd usually use 8 or 9 holes in a 2m length. For little lettuces, basil and other smallish plants, you can fit 10 holes down the length. Beware: If large plants are grown in cramped channels, all their root systems intertwine. Separating plants at harvest time is a nightmare and results in many bits of root lodging in your system's filters.

Do not be tempted to grow plants all the way down to the end: The root systems of the last plant will clog the drainage hole. We cut a hole over the drainage hole to allow inspection, fitting and clearing. This inspection hole is centred at 5-6cm from the end, and is large enough to pass an outlet fitting and a fat finger or two simultaneously.

So for 10 holes plus aforementioned inspection hole down a 2m pipe, you separate each hole by 18.5 cm. For a 9 hole length, 20.5cm and for 8 holes, 23cm. Mark your inspection hole and start from there. Some people stagger the holes off-centre when packing really densely for seedlings or crops like spring onions, but I've not tried it myself.

The ends are blocked off with end plugs obtained from the same supplier as the pipe. A piece of 4mm irrigation pipe goes in the top of the high end, and we originally used a rubber grommet to seal the 14mm outlet pipe at the low end. Additional sealing around the grommet was added when I fit them badly. The sealing around the end plugs was done both with PVC cement and a clear sealant that works in the wet - much less hazardous than PVC cement but far more messy and not recommended (see below). Ask your local DIY store if you need some in a leaky emergency.

As time progresses and temperatures started to rise, the rubber grommets lost their seal. A more expensive solution had to be fitted instead involving flanged tank outlets with 14mm connectors on. Some of the end plugs also started to leak as the troughs expanded. These leaks were from end plugs which fitted inside the troughs rather than capping over the end. I would recommend the use of the more expensive end caps rather than end plugs, and flanged tank outlets. Make sure your inspection holes are large enough for you to drop the tank outlet into - mine weren't and it's really hard to enlarge them in situ.

Prolblems also developed with the clear sealant. Plant roots were able to gain a purchase on the relatively soft sealant and work their way through. Eventually a seal breach occurred and nutirent peed forth. As this happened at the inlet end, we were able to wrap PTFE tape around the end plug (note: it was a plug that failed, not a cap) and ram it home to effect a reasonable repair.

Aggregate Troughs

Another way of growing hydroponically is to use troughs filled with some form of inert material. Gravel with an average diameter of between 4mm - 8mm is preferred, though you need to check the material carefully. You don't want things that dissolve or react with the nutrient solution, so limestone is out. Pummice is OK if well washed, but as it is volcanic can hold some residual sulfur and goes green with algae quickly anyway. Scoria has the same problem to a lesser extent, but roots grow into the bubbles in scoria making it difficult to reuse.

We prefer to use small road chippings, but these are not always available. There is a form of bedding mix that is used to lay pavings on that can be had in larger sizes. The down side is that it comes with some sand in, which has to be washed out. That's what kids are for :)

An old concrete sink is an ideal receptacle; it is opaque preventing algae growth, doesn't dissolve or react, has a ready-made drainage hole and holds a lot of aggregate. Unfortunately they're hard to come by and a bit bulky for our deck but we had another source of container available: 20 litre black plastic drums of "Forexpan - S", a foaming agent used by the local fire brigade. Vik is a member of the brigade and the CFO was only too happy to get rid of the old drums.

Be wary of recycling drums though. Forexpan is unpleasant when concentrated, yet is biodegradable and washed off easily. If you use other drums, make sure you know what was in them last and take the appropriate precautions. Non-biodegradable detergent tends to cause alkaline residues in the plastic and needs flushing with boiling water.

A 25l tub for hydroponics We cut some of our containers in half and use one half to make a deep drip-tray. A grommet and pipe then go in the dimple in what was the top, so the nutrient solution is taken off a few centimetres above the bottom. This allows any sand or other fragments that could damage the pump to settle out in the drip-tray.

To dispense the nutrient into the aggregate, we use a spider-like distributor made from a 4mm end-line dripper. This fitting has 4 holes around its perimeter which normally drip water and a stalk to connect it to a 4mm piping system. We drill the holes out to 4mm and put fine piping in them. A few extra holes can give us an 8-way adjustable distributor if many small plants such as garlic bulbs are planted, but try to make sure that the ends of the little pipes are all at the same level or the lower ones will get the majority of the flow.

The 4mm pipe carrying the incoming nutrients actually enters the container half-way up, below the surface of the gravel. This is done because water dripping through the surface would make the gravel go green with algae. By submerging the piping below the surface, we can saturate the gravel a couple of cm down creating good growing conditions. Currently we have strawberries, garlic, sugar beet, chervil, advocado and snow peas in these containers.

The MkII Aggregate Trough

The drawback with filling these containers is the sheer volume of medium that needs to be sterilized on an annual basis. To circumvent this, experimented with little pots of volcanic chip that are saturated from above by a network of 4mm tubes normally used for irrigating hanging plants. A tap allows the flow rate to be controlled, while 2mm tubes that are easily bent while warm place the nutrient precisely. The 4mm tubes need joiners, but the 2mm tubes fit nicely inside the 4mm ones. The nutrient solution drips through the tubs of chips and down the roots, which hang down like an erie white forest into the dark tub below. Strawberries do well in this medium, though we are experimenting with various brassica. On a larger scale we have also planted a paw paw in a mix of 2cm pebbles and chip which seems to be doing well (2 metres plus tall, fruiting and getting bigger).

The MkII is a much more suitable container for plants, and we have now produced variants with only two holes in for growing larger plants. This technique seems to combine the best of aeroponics and hydroponics in one. The old Mk I troughs have has the aggregate scopped out and are now relegated to growing watercress, and a load of strawberries I've not been motivated to clear out.

Filters

Originally we didn't have any filters in our system. All worked well for about 6 months and then the occsional tube would block - usually where we'd rammed a 4mm tube into a 6mm tube - the easiest way of jointing them. Then we started getting blockages at the rate of one a week, so we fitted a filter for a whole NZ$10 - about the same cost as 4 bottles of beer. These are the same filters as are sold with garden irrigation kits; long, black cylinders with a perforated white cyclinder in the middle. These need to be watched carefully as we have had several near emergencies when the filter has clogged solid with unexpected debris. This can be caused by removing plants from the beds, or by local foliage shedding vast quantities of leaves, fibres, seeds and so forth.

Controlling The Flow

The ultimate flow control on your system is the pump. Turn it off, and the flow stops - so does the noise of the pump, and so some kind of timeswitch is usually fitted. I went a little bit sophisticated and run the thing off a house controller computer I built. Mere mortals can make do with a cheap, plug-in mains timer from your local hardware store. Pick the six hours at night that you'd most like to be asleep in, and let the timer turn things off. If you run many aggregate beds, these benefit from extra oxygenation so it might be worth turning the pump off briefly in the day (not in the midday sun!) to allow air into the gravel beds.

Flow into the individual troughs needs to be controlled too. Maybe one trough is hogging all the water; try putting a bit of 2mm pipe in the end of the 4mm inlet pipe to slow down the flow in that trough. Or go the whole hog and fit one of those little 4mm taps sold for garden irrigation systems.

If you're a tinkerer like me, it might be worth fitting taps to turn parts of the system off. But taps are expensive, so don't plan on sticking them everywhere.

Water also needs to flow into your system, because the plants will use it all up. Whatever device you use has to be saltwater rated unless you can guarantee it won't go in the nutrient. When we started our system in the Autumn, the plants weren't very thirsty and we seldom had to top up the water. As we moved through into Spring, we hooked the bucket up to the garden irrigation system and hoped that the hydroponic system and the garden stayed roughly in synch. They did, more or less but as more turned to less I installed an all-plastic top-up valve similar to the things that lurk in toilet cisterns. I installed it upside-down at the bottom of the tank, with the ball bobbing on the surface and tied to the lever with a piece of string. This allows us to set the maximum water level by changing the length of the string.

As an experiment in recycling, we have also vented the water from our air conditioner into the nutrient tank. As this is distilled water, it did not have a detrimental effect on the plants. However, the sheer volume of water caused the nutrient bucket to overflow so we disconnected it.

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