Operating Your System.

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Hydroponic garden.
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A closer view.
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The Author's pump.
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The Author's nutrient tank with pump under cover.
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Cos lettuce. When one comes out, another can be planted immediately.
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On this page, you will find details on how to operate your system.

How much sand do I need?
The sand level should be about 25mm (1") below the edge of the cut-out. This will allow a modest amount of flooding before the system overflows. The vertical drain tube in the end water box should be set slightly below the sand level.

How much nutrient do I need?
You need just enough to submerge the growing medium (sand). You can do this with plain water. Turn the pump on with a running hose in the nutrient reservoir, and turn the hose off when the sand just submerges. If you cannot use a hose, just add water with a bucket. Now, let it drain back into the nutrient reservoir and mark the level on the inside of the nutrient reservoir with a permanent felt pen.
If you have more than one growing module, it is necessary to ensure that each module is receiving its fair share of water. Please see Tip # 2 on the previous page, Hints for Success.

How big should my pump be?
If your pump can empty the reservoir into the growing modules in say 5 minutes, it is big enough. Soon after starting to pump, drainage will start and the pump must work faster than the drain, otherwise it may never fill. Another factor to consider in selecting pump size is the head (the height you are lifting the water). If you are pumping up to say 2.5 metres, you will need a decent sized pump. If the head is only 600 mm or so, you may get by with a small pool pump or a fountain pump.

Details of the Author's pump.
It is an Onga Pump, Model 413, 240 V, 2.5 amp, 2800 rpm, combined pump and motor, made by Onga Pumps in Melbourne, Victoria, Australia. It is suggested that you have a look at the Onga website for full details of the pump.

Onga Pumps.

How often should the pump run?
In South East Queensland, you will be able to get by with just four pump-ups per day. Suggested times are 8:00am, 11:00am, 1:00 pm and 3:00pm. Your timer should be set to turn the pump on at these times, and off as soon as the nutrient reservoir empties when the growing beds flood. This is a total of about 12 minutes per day.

If you live in a hotter climate, you may have to have five or more pump-ups per day. It pays to keep the nutrient reservoir cool, so locate it in the shade if possible. Consider using shade cloth over the growing modules if your climate is hot. If shade cloth is not available, try coconut fronds or anything else to give at least some shade to your plants. Plants do not like hot nutrient solution.

Another reason to keep your nutrient solution cool is that gases that are soluble in water, are more soluble in cool water than they are in hot water. Soluble solids, on the other hand are more soluble in hot water than they are in cool water.

Do I need to aerate the nutrient?
There is no need to aerate the nutrient because the system does it for you. When the sand bed drains, an equal volume of air is sucked down to the plants' roots. Each particle of sand and each small hair root is covered in a film of nutrient solution, which is enough to sustain moisture levels until the next pump-up. The sand bed should not be allowed to dry out. If it does tend to dry out, the remedy is to add one more pump-up.

What type of sand is suitable?
Bedding sand, sold as filling for house foundations that have been dug too deep, is ideal as the particles are well rounded. Another suitable medium is 5 mm screenings, composed of crushed rock with a coarse feel. Any fines should be screened out and used elsewhere in the garden, as they tend to hold too much water. The Author recommends digging planting holes in the coarse sand with the end of a knife blade; it saves fingers!

What is the best way to plant?
Using this system, planting can be done three ways.

(1) Sow seeds directly in the sand bed where you want the plants to grow. It pays to mark their positions with dead twigs so you do not sow anything else on top of them.

(2) Sow seeds directly in the sand bed about 40 mm (1.5") apart as a seed bed and mark with dead twigs. When large enough to transplant, carefully dig them out with a large metal spoon, without disturbing too much sand, and transplant them into their final growing position.

(3) Purchase or grow your own plants in punnets of seed-raising mix, and thoroughly wash the soil from the roots before planting into holes dug in the coarse sand bed with the end of a knife blade. The spacing is entirely up to you, however, smaller plants can be spaced closer together than larger plants. When transplanting in hot weather, it may pay to remove some leaves or even cut some back somewhat, as the plant is likely to go limp.

Timetable for adding nutrient solution, pH testing and cleaning out.
Please see the "Hints for Success" page, and go to Tip # 6.

The next page gives a layman's explanation of pH and the pH scale, and why controlling pH is so important.

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