Green walls are rapidly growing in popularity for their ability to bring the serenity of nature into the madness of our expanding urban environment – they 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 need to make is to either 'go hydroponic' or not Ie to use soil or not? I am biased towards one type in particular but my views may at least help you to ask the right questions before you buy.
Hydroponic Green walls – deliver nutrients to plant roots via water not soil. Small scale systems for domestic use can be reliably easy to maintain. However, larger hydroponic systems can be quite complex as well as more expensive to 'run' if they need professional maintenance. Here are a few factors to consider when trying to decide which way to go. If you 'think like a plant', the decision will be easy but maintenance rates as a big factor in my choice.
Water usage – A soil based green wall's natural ability to retain and even distribute water makes it more water conservative and much easier to maintain, especially if watering is an option.With hydroponic systems, a constant flow of clean, aerated water and nutrients is required to keep your plants healthy. The irrigation methods in large hydroponic systems can be quite complicated and require frequent expert attention. Pump failure without backup power could see plants lost in a matter of hours whereas a soil based green wall is more forgiving should shutdown, with a window of days for survival rather than hours. Another challenge you face with hydroponic installations is maintaining water temperature and pH levels which are extremely important, especially outdoors in warm climates. Changes in water temperature will affect your plants' ability to survive. A soil based green wall system consumes less water, does not have to use re circulated 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, whether this is on rocks, in soil or in synthetic materials like those found in hydroponic systems. One problem that can occur when using a hydroponic green wall system is that the plants may not create a strong enough root system to be sturdy and need weeks of 'training' to defy gravity. A soil based system with a large root space encrypts the growth of an intensive, strong root system. The price you pay for this bonus though is that the system will probably be heavier than the hydroponic one overall so check that your wall / fence / deck can take it.
Nutrients and oxygen – Even expert botanists sometimes 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 systems in which a balanced solution of nutrients must be added to the water at specific times through the growth period. Even the smallest fluctuation at the wrong time can destroy your plants in a matter of days. Soil based green wall systems are much more forgiving in this area. The soil acts as a natural buffer and plant pantry, absorbing excess nutrients still providing them to the plants as needed.
Another vital factor for success with hydroponic systems is the need for the right amount of oxygen at root level. Plants 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 hardworking 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 green wall systems are more resistant to the spread of disease than hydroponic systems and can there before be less risky. In hydroponic systems, where the plants' roots are more exposed to water that regularly re circulates, algae / bacteria can quickly travel to all plants via the system's irrigation superhighway. A disease called 'pythium' which causes roots to rot, is almost impossible to eradicate even with intensive 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 systems require electric pumps that constantly re circulate water from a reservoir at the base to carry nutrients to all the plants. Due to the sensitive nature of a hydroponic 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 through the system, reducing risk of water-borne disease. Timers and pumps can be used in soil based systems too but only intermittently as needed. Without it's installed indoors where lights may be needed, hand watering your soil based green wall can eliminate the need for a power source all together.
Maintenance – Maintenance is one area where soil based green walls systems really shine. Some simple irrigation, fertilizer twice a year, some tip pruning and replacement of the odd plant now and again means you can spend more time enjoying your lushness than tending to it. The ongoing demands of cleaning parts and monitoring nutrient mixes for a hydroponic system are enough to scare some people off. Owners of large hydroponic systems typically hire a professional team to maintain their green walls which adds to the ongoing cost. Soil based green walls require much less maintenance since they're able to regulate water evaporation and nutrient delivery something on their own.
While hydroponic green wall systems have their advantages, especially in large corporate settings, many people like me prefer the 'hands-on' nature of a soil based system. I think these are more cost-effective, easier to maintain, enable multiple uses and allow for the personal approach that gardeners know and love. After all, what fun is growing plants if you can not play in the dirt?