Greenwall Systems: Soil based or Hydroponic?

Vertical Garden and Greenwall systems are rapidly growing in popularity due to their ability to bring the healing serenity of Nature back into the life sapping madness of our ever expanding urban environment. Greenwalls naturally purify the air and have now been proved to reduce a building’s heating and cooling costs. With so many options available it can be difficult to decide which kind best suits your needs but one of the first decisions you'll be faced with is whether to ‘go hydroponic’ or not i.e to grow in soil or water? I am biased towards one type of Greenwall system in particular but my views may at least encourage you to ask the right questions if you are undecided.

Hydroponic Greenwall Systems deliver nutrients to plant roots via water not soil. Small scale Greenwall systems for domestic use can be relatively easy to maintain, even though they still require a constant power/water supply. However, larger hydroponic systems can be quite complex to install as well as more expensive to ‘run’. Here are a few basic factors to consider when trying to decide which Greenwall system is for you. If you ‘think like a plant’, the decision will be easy and maintenance looms large as a deciding factor for me.

Water usage

A soil based Greenwall system's natural ability to retain and evenly distribute water makes it more water conservative and much easier to maintain than a hydroponic Greenwall system, especially if hand watering is an option. With hydroponic systems, a constant flow of clean, aerated water and nutrients is required to keep your plants thriving. The irrigation methods in large scale hydroponic Greenwall systems can be quite complicated and require frequent expert attention. Pump failure without backup power could see plants die in a matter of hours whereas a soil based system is more forgiving should irrigation stop, with a window of days for survival rather than hours. Another challenge you face with hydroponic Greenwall installations is maintaining water temperature and pH levels which are extremely important for plant health, especially outdoors in warm climates. Changes in water temperature will affect your plants ability to survive. A soil based Greenwall system consumes less water, does not have to use recirculated water and allows for more irrigation options which help to stabilize moisture levels and temperature of the soil.

Plant support and weight

Plants naturally produce incredible root systems to anchor themselves to whatever they are growing in, whether this is on rocks, in soil or in synthetic materials like those found in hydroponic Greenwall systems. One problem that can occur when using a hydroponic system is that the plants may not create a strong enough root system to be sturdy and often need weeks of ‘training’ to defy gravity after being plugged into the vertical Greenwall ‘horizontally’. A soil based Greenwall system with a large root space encourages the growth of an extensive, strong root system and the plants grow in their natural ‘vertical’ plane from the start. The price you pay for this bonus though is that the soil based Greenwall system will probably be heavier than the hydroponic one so check that your wall/fence/deck can take it.

Nutrients and oxygen

Even expert botanists occasionally struggle with the proper balance of nutrients for their plants, regardless of whether these grow in soil or water. This is especially true in hydroponic Greenwall systems in which a balanced solution of nutrients must be added to the water at specific times throughout the growth period. Even the smallest fluctuation at the wrong time can destroy plants in a matter of days. Soil based systems are much more forgiving in this area. The soil acts as a natural buffer and plant pantry, absorbing excess nutrients yet providing them to the plants as needed.

Another vital factor for success with hydroponic Greenwall systems is the need for the right amount of oxygen at root level. Plants can die of suffocation due to anaerobic activity caused by mismanagement of irrigation, nutrient mixes and microorganisms. In soil based systems, oxygen is supplied through a natural process – it becomes aerated by hard working little microbes giving the roots the TLC they need.

Risk of disease

Combatting pests and disease is an ongoing problem for any gardener. Soil based Greenwall systems are more resistant to the spread of disease than hydroponic Greenwall systems and can therefore be less risky. In hydroponic systems, where the plants’ roots are more exposed to water that constantly recirculates, algae/bacteria can quickly travel to all plants via the system’s irrigation superhighway. Root rot or ‘pythium’ is almost impossible to eradicate even with extensive disinfecting. Something as simple as unsterilized tools is enough to bring your hard work, as well as your emotional stability crashing down in a couple of days.

Power usage

Hydroponic Greenwall systems require electric pumps to recirculate water from a reservoir at the base to carry nutrients to all the plants. Due to the sensitive nature of a hydroponic Greenwall system, a power failure could be devastating. With a soil based system, you have the option of regularly hand watering your plants with ‘fresh’ water and allowing the soil to carry the water throughout the system, reducing risk of water borne disease. Timers and pumps can be used in soil based Greenwall systems too but only intermittently as needed. Unless it's installed indoors where lights may be needed, hand watering your soil based Greenwall can eliminate the need for a power source all together.

Maintenance

Maintenance is one area where soil based Greenwall systems really shine. Undemanding irrigation, fertilizing twice a year, some tip pruning and replacement of the odd plant now and again means you can spend more time enjoying your lush Greenwall than tending to it. The constant demands of cleaning parts and monitoring nutrient mixes for a hydroponic system are enough to make you revisit toddler training techniques –with no pay off. Owners of large scale hydroponic Greenwall systems usually hire a professional team to maintain their Greenwalls which adds to the ongoing cost. Soil based Greenwall systems require much less maintenance since they're able to regulate water evaporation and nutrient delivery somewhat on their own.

While hydroponic Greenwall systems have their advantages, especially in large corporate settings, many people prefer the hands-on nature of a soil based system. I think this type of Greenwall system is cost effective, easy to maintain, enables multiple use and allows for that personal interaction that gardeners seek and love. After all, what fun is growing plants if you can't play in the dirt?

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