Passive hydroponic systems are simple setups that have no moving parts. These systems work without the use of electricity. There are no pumps, timers or switches in a passive system.
Instead of soil, you will use a grow medium. Glass pebbles or clay aggregate, are 2 examples of grow media. Your medium will support and set the plant upright and anchor the root zone in place.
Advantages of passive hydroponic systems
- Ideal for beginners
- Simple to build with few parts
- Does not need electricity
- Soil borne pests are not an issue because no soil is present
- Easier to water and feed the plant
- When the mixture levels are low, we simply top off the reservoir
- Eliminates a lot of guesswork and the risk of over and under watering your plant
Disadvantages of passive hydroponic systems
- Not suited for larger or fruiting plants
- Not an automated system
Ideal plants for passive hydroponic systems
- Lettuce and Herbs
- Small non fruiting plants
- Houseplants
Method of growing
All passive systems are a variation of 2 growing methods. They are either water culture or wick systems.
Water Culture
Water culture is generally done in one of two ways. There is the single container method or double container method.
Single container
With the single container method, the plant and nutrient solution are together. The container does not have drainage holes and is water tight. It needs to be made from materials that are non-reactive to liquid fertilizers. You should avoid containers made from metal.
Part of the plant’s root bed sits in nutrient solution at all times. The part of the root bed that’s left out and exposed will take in the oxygen required for healthy growth.
You can track water levels without disturbing your plant in a glass container such as a jar or vase.
Double container
The double container method uses two containers. The plant and nutrient solution are separate from each other.
One container does not have drainage holes and is water tight. This is the reservoir for the nutrient solution.
The second container is a slightly smaller container than the first. It will have perforated holes and sit within the other that is water tight.
Your plant is set in the perforated container. It will keep your plant from being completely submerged in the nutrient solution.
The perforations allow oxygen to flow within the root zone. They also allow roots to grow beyond its container. This becomes important when solution levels are low. Roots will grow to reach to absorb nutrients below.
Growing medium for water culture
Clay aggregate, is also known as hydroton or expanded clay balls. It’s a popular choice for water culture, to anchor a plant in place.
It’s easy to work with, light weight, and will not crush delicate root systems. Yet, it’s heavy enough that it can support the weight of even larger plants.
Hydroton is reusable so long as you wash and sterilize it between each grow.
Important note about using clay aggregate
When using hydroton for the first time, you’ll need to rinse it thoroughly. This is to flush out all the clay dust that accumulates during transport of the product.
Wick systems
Wick systems keep plants and nutrient solution separate from each other. The set up is similar to the double container method.
The nutrient solution is kept separate from the plant. A wick acts as a bridge between the 2 containers. The nutrient solution travels through the wicking material to get to the plant’s root zone. It works on the principles of capillary action .
The wick
How well your plants thrive growing in this system depends on the wick. It needs to be very absorbent so that nutrient solution can travel up from the reservoir to the plant root zone.
Where one material will deliver nutrients with ease, another will have more resistance. Not only is the type of material used important, but also the number of wicks used for each plant. The wick must keep up with the plant’s need for water and nutrients.
Common material used for wicks
- nylon rope
- cotton rope
- braided polyurethane yarn
- felt strips
- mop head strands
- tiki torch wicks
- fabric strips from old blankets or clothing
Grow medium for wick systems
For wick systems, you want a growing medium that has some capillary action of its own. It needs to draw nutrients to areas in the root zone that are further from the wick.
If a grow medium with no capillary action is used, you would need a handful of wicks fed throughout a plant’s root zone. Even then, your nutrient solutions wouldn’t be evenly distributed. Your plant will run the risk of starving.
A mixture of sand, perlite and vermiculite is a better choice for wick systems. This mixture can absorb nutrient solution from the wick and draw it to other areas of the root zone.
This will distribute your nutrient solution more evenly and promote healthier growth.
If you want to use a net cup for your plant, you can line it with landscaping fabric to avoid sand leaching out.