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DIY Hydroponics - Passive Hydroponics

Really Simple Passive HydroponicsHydroponic methods are usually divided into two categories, passive hydroponics and active hydroponics. The difference between the two is determined by how the nutrient solution is delivered to the plants. An active hydroponics system relies on a pump to deliver and recirculate the nutrient solution to the plants, some examples being flood and drain, top feed and NFT. Usually with active hydroponics the nutrient solution is recovered after circulation in some sort of reservoir to be pumped around the system again.

Passive hydroponics on the other hand has no pumps or moving components and the nutrient delivery relies on capillary action or the plants roots growing into the reservoir. Carefully managed a passive hydroponic system will result in lower nutrient solution usage and they are far less likely to suffer any issues like pump failure. The plants grown in a passive system will grow at least as well as being grown in soil however they lack the aeration/flooding cycles of an active hydroponic system. So we can summarise by saying that passive hydroponics is cheaper and less complicated than active hydroponics however there is some trade off in plant growth rates. With few exceptions most passive hydroponic systems are hand watered.

You can make a passive hydroponics system out of just about any container. The silverbeet on the right is grown in a window planter box. In the top picture you can see where I have plugged the original drain holes with a good smear of silicon. If you use silicon make sure its suitable for use in aquariums and then give it seven days to cure and a good rinse off before you use it. New drain holes were made with a drill higher up the planter box so that the high water mark is now two inches below the top. The planter box was then filled with hydroclay but you can use perlite, gravel or most other mediums and fine tune your watering schedule accordingly. These silverbeet seedlings were started in a small rockwool cube and planted out when they were well established and had roots growing out of the cube.

The silverbeet were watered once a day with an appropriately mixed nutrient solution. The solution was applied with a watering can until it started to dribble out of the drain holes we had drilled. One day a week they were watered with plain water to avoid nutrient build up. Disaster struck in the form of a heatwave with temperatures exceeding 40 degrees celsius every day and we started to water with plain water at 3pm as well because the reservoir was drying out thanks to evaporation. The final picture in the silverbeet group is from the fifth day of the heatwave, at the time the plants had been in the planter box about six weeks and we had already had several meals out of them. Silverbeet is an excellent pick and come again vegetable and generally if well managed we will get several months of productive growth out of them. Pick the outer leaves and stems but always leave at least four or five leaves so the plant will recover and continue to grow.

Different Approaches to Passive Hydroponics

Spring onions in passive hydroponicsThere are so many different ways you can make passive hydroponics work for you its hard to list them all. Different plants have different requirements and you can tailor your set up to suit your plants needs. Our spring onions to the right are grown in a rockwool slab in a take away food container. Spring onions have pretty shallow roots and arent fussy about plant spacing so this simple method is ideal. The spring onions are broadcast seeded into the cube and as they grow big enough to use we thin them out with the thinnings going into soups and sauces. You can also see in this picture our silverbeet seedlings in seedling cubes in the ice cream container.

Cabbages in a rockwool slabThese cabbages are grown in uncut rockwool slabs in a hydroponics tray. The tray has no drain holes and it is filled daily with the appropriate strength nutrient solution. Rockwool slabs are perhaps a little under rated in passive hydroponics. Even when wringing wet they still hold about 30 percent air and the nutrient solution climbs the cube well by capillary action, resulting in a relatively ideal ratio of nutrient and air around the roots giving us good healthy plants. They taste just great and we have a hard time keeping cabbage moths off them their so good. A good dusting with derris vegetable dust every week keeps the caterpillars and moths at bay.

Cabbages in a rockwool slabs and pots with gravelAnother variation perhaps on the planter box theme, we have our next generation of cabbages coming up. The one on the right is grown directly in a rockwool slab and watered by capillary action from the nutrient in the planter box. The cabbage on the left is grown in a seedling cube and potted up to a pot of hydro clay. It is watered once per day with nutrient solution applied to the seedling cube until the roots have reached the high water mark of the planter box. Once it is able to reach the nutrient solution by itself the planter box is filled every day to the halfway mark. Side by side they will usually grow at a similar speed though the one in the rockwool cube perhaps just a little faster. Vermiculite also works well in a pot in this simple passive hydroponics system.