I found some research that I did with a team on green walls and wanted to share it more broadly. We ultimately did not develop the wall, but we learned a lot about requirements and considerations. Without ado, here goes...

Selecting Plants

Questions to keep in mind:

1. What plants work best for your climate and specific area the green wall will be placed at? (Maybe try to aim for plants that require less water)
   1. Wall direction
   2. Shade or sun
   3. Climate
   4. Accommodate soil drainage needs
2. Lifetime of the plants?
3. Do you want to have native plant species? Diverse plant species?
4. Preferences for color palette, edibility, non-toxicity, fragrance?
5. Do we want borders? (maybe use twining climbers)
6. What is the mature height of the plant? What is your height limit?
7. What are maintenance requirements?

Caring for Plants

Some general tips and also succulent-specific advice.

Light

• Most varieties need at least half a day to a full day of sunlight.
• Most cacti and succulents like bright light, but not all can tolerate intense, direct sunlight, especially in conjunction with high temperatures. The intensity of the light that a plant will thrive in depends on the species.

Water

During their growing season, these plants like regular watering and fertilizing. For most, the period of growth is from Spring into Fall. Many plants rest (stop putting on growth) from late Fall to early Spring, when temperatures are cool and daylight length is short, and during mid-Summer, when temperatures are at their peak.

• While growing, cacti and succulents should be watered at least once a week. During each watering, give the soil a good soaking, so that water runs out of the 'drainage holes' of the pots.
• During the growing season, a balanced fertilizer, which has been diluted to 1/4 strength, can be added to the water for each watering. (A balanced fertilizer is one that has roughly equal proportions of Nitrogen, Phosphorous, and Potassium. A 10-10-10 fertilizer diluted to 1/4 strength is ideal.)
• When the weather cools and day-length shortens, plants enter a rest period. During that time, increase the interval between watering, and let the potting mixture dry out between watering.

Soil

• Succulents need good draining soil. For container planting, you can purchase cactus soil or incorporate sand, gravel or volcanic rock for better drainage.
  • The best way to achieve this is by adding horticultural-grade sand and grit to the compost component of the soil.
  • Many believe that a good starting ratio for the mix's components are one-third compost, one-third horticultural-grade sand, and one-third grit.
  • The sand component should be horticultural grade, relatively coarse, and sharp. Never use non-horticultural grade sand, such as fill sand, as this is usually not washed, and can contain, among other things, salt.
  • For the grit component, most people agree that horticultural pumice is the best. It is also not widely available, and can be expensive if you can find it. Some other materials that can be used include pearlite, porous gravel, and lava fines.
• The container you are planting in should have a drainage hole or put crushed rock on the bottom before your planting medium.

Fertilizer

Most succulents need very little fertilizer. Watering with a well balanced fertilizer once a month will be all they need.

Irrigation

Considerations

• Technically they can be watered manually if there will always be someone to do that
• Because of gravity, the bottom tends to be overwatered and the top underwatered
  • Put plants that need more water at the bottom
  • Set up an extra cycle for only the top portion
• Roots should not soak in water
• Irrigation system is different depending if we use a bagged system, felt, or soil
  • Felt: water tends to collect at bottom
  • Husk (coco): holds no water
• First question you have to ask yourself is: Do I want a reservoir or do I want to use potable water source. Once you decided on what the source of irrigation water will be the next step is to calculate how many zones and in what configuration the wall will need.

Types of Irrigation Systems

Both Types of Irrigation

• Can be operated with a timer/controller that tells it when to turn on/off
• Need fertilizer (try bioSoil or Add-It), beneficial bacteria

Drip Line Instructions

1. Cut your riser tube to the height of the wall.
2. Cut your drip line to the width of the wall.
3. Install your dripline every second row of pods.
4. Add your drip line joiners, making sure the drip emitters is centred over each pod.
5. Punch holes in riser tube for the dripline.
6. Attach your drip line to your riser tube, cable tie riser tube to spare clip holes on plates.
7. Plug in your end plugs to your drip line and riser, attach riser to tap and irrigation controller.
8. Program timer and let it grow!

VIDEO

Materials Needed

• Riser tube
• Drip line
• Drip line joiners
• Tube end plugs
• Propagation timer/controller
• Tools for tube cutting and hole-punching
• Fertilizer
• Fertilizer injector
• Brackets or hooks to attach tube to wall

References

http://www.ambius.com/blog/how-green-walls-work-irrigation/

http://agreenroof.com/wp-content/uploads/2013/06/Hydroponic-irrigation.pdf

http://www.popularmechanics.com/home/how-to-plans/how-to/g847/how-to-start-a-vertical-garden/