What Is Passive Hydroponics?
October 2, 2017
You can’t get a more simplified form of hydroponic growing than a system that uses passive hydroponics principles. In its most basic form, it provides water only beneath the plant roots. It doesn’t recirculate. The nutrient-rich water is there until used by the plants. There are two types of passive hydroponics: soilless and soil. Not dirt, like you, find on the ground, but soilless potting mix, which in the hydroponic world is known as ‘soil’. In true soilless passive hydroponics, all the plant’s nutrients are available only through the water in the reservoir. Yet, when using a potting mix, both the media and the reservoir can hold nutrients or supplements. The method you choose to use guides your choice of growing media. There are several styles referred to a passive hydroponics. If it is hydroponic, either the plant is suspended over the nutrient solution and relies on its roots to access it, or a wick draws the nutrient-rich water up to the media for roots. First, we have the Kratky Method, which employs plants suspended into the nutrient tank. The second method known as wicking works just like capillary action in the natural world of plants but allows an oxygen zone between growth media and nutrient solution. You see wicking used in traditional container gardening too – in seedling trays with the capillary mat. And the capillary action is found in self-watering planters like Earthbox. (But self-watering planters are not passive hydroponics. Hydroponics mixes nutrients with the water and uses inert growing media.) You can’t use coir or peat in a Kratky setup, but you can in a wicking system. Why? The smaller particles will fall through the holes in a net cup designed to contain aggregates like clay pellets or pea gravel. But you can wick into gravel and vermiculite using cotton or wool fabric, natural rope, and even oil lamp wicks. The Kratky method makes your plants seek out water and nutrients. Young seedlings in this passive hydroponics setup have immediate access at the bottom of the suspended net cup, but as the root system grows larger and consumes the reservoir supply, the water level drops and the roots chase it down. Passive hydroponics that uses a wick, however, brings the water to the plant.
You can apply both types of passive hydroponics to single and multiple plant systems. You’ll find people growing this way in Coke bottles, canning jars, 5-gallon buckets, coolers, tubs, barrels, and wooden raft boxes lined with plastic. Don’t forget the as above, so below principle… choose reservoir containers to fit the plant and its roots. For instance, slicing tomatoes aren’t suited to a big coffee can – a 5-gallon bucket works, but a 20-30 gallon barrel is better. You can grow most fruiting and leafy crops indoors or outside using passive hydroponics without any electricity at all – as long as you’ve got plenty of direct sunshine. However, you could find some cultivars just not wanting to perform in a Kratky setup, like my lettuce trial a few years ago. I grew 2 green and 2 red Salanova lettuces in coffee cans, and while the Green Butter plants stretched their roots and followed the water, the Red Sweet Crisp did not! We suspect that the red type I chose just wasn’t a good Kratky method selection. It grows perfectly well in soil or pots, and in hindsight, I realized that transplanting into a wicking setup would quickly correct the issue. Whatever you choose to create a homemade passive hydroponics setup in, make sure the walls aren’t transparent. You don’t need light inside your reservoir. Besides roots avoiding light, algae will move in and use up all oxygen your plants are relying on. So, paint those Mason jars and soda bottles to block out sunlight. If you want them pretty, get creative. But remember that dark colors are better than light ones. (White or pastel a must? Paint over a dark color.) Not everyone loves a DIY project, and for them, there are professionally made passive hydroponic systems on the market. My favorite is more sophisticated than a precisely molded tub, and it’s scalable, so you can start small with 2 or 4 plants and add units as your garden grows. That’s the AutoPot Easy2Grow system, which gives the gardener some distinct advantages over both the Kratky and wicking methods. You can use it as a hydroponic system with plain coir or peat growth media, or a self-watering garden when planting in a nutrient-rich potting mix. All your individual pots are separate from the reservoir. Moisture and nutrients arrive in the growing media through gravity and a unique mechanism in the tray beneath each pot. The mechanism only allows more moisture to enter when the media is dry. This prevents possible root disease problems from an overly soggy potting mix and allows you to keep the reservoir in a cooler place than your plants. Reservoir temperature is important, especially when growing outdoors in summer’s heat. You can’t cool off a heat-stressed plant with hot water! Images courtesy of Pawat Polar Bear, Farmer Tyler, Qfamily, dianemv, Sincerely Sara D., and AutoPot (respectively).
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