Green wall in apartment doesn't quite get direct sunlight, can I redirect the light somehow?

Question

I put together a lattice in my (4th floor) apartment's living room to try and grow some climbing plants on it, because the room faces west and I thought it would get a lot of light. Indeed during the day it is quite bright, but I realized that most of that light is actually reflected off the buildings on the other side of the block. In the evening, the sun beam does not quite reach the full extent of the lattic, because it dips below the buildings across the block before it is able to reach up towards the bulk of the green wall. I should have measured better, but it is too late since I built it, and so I'm willing to try whatever is feasible to make it work.

Can I buy some kind of mirror or prism that can redirect a sufficient amount of sunlight directly onto the green wall? I don't really know how to articulate this into google, searching for prisms or reflectors typically turns up science teaching equipment or vehicle reflectors.

I have tried to draw the scenario in MS paint. The green part on the left is the plant wall and the blue bit on the right is the window (floor-to-ceiling). It's not quite to scale, there is a lot more space between the two buildings, but I think this captures the problem of angles.

Answer 1

I'd consider alternative solutions over mirrors. These also cause glare in your living room area, meaning you might get blinding reflections into your seating area or on the TV.

The angle of the sun varies both during the day and over the year (how much depends on your location/latitude). For that reason, anything reflective should additionally be tracking the sun, to keep said glare on your plants (and out of your eyes). In your case most of the sunlight entering your room was additionally reflected off of nearby buildings, which would make it an even more challenging project.

I would therefore suggest two alternatives:

1. Move that plant lattice close(r) to the window

You can screw together a simple wooden frame, or put it on the back of an existing bookcase or cupboard. It depends on your room layout of course if this will work, but indoor freestanding vertical gardens are definitely a thing now.

The best would be something on wheels. Because in our case the difference between high summer and the dark of winter is a factor 6 in solar irradiation at solar noon, we move some of our plants near the windows in winter, and deep in the room in summer.

You can visually establish what they need by considering if they're getting light green or dark green (a lot of plants change the amount of chlorophyl depending on available light), and if leaves start withering at a faster rate than usual (radiators underneath windows in winter for one can cause this).

2. Use plants that thrive in indirect sunlight.

There are a lot of forest dwellers that don't normally see much sunlight. These could be ferns, orchids and plenty of others. Specifically for climbing plants this site has a few dozen suggestions. I'll list a couple from there that I personally like (do browse their full list though):

• Heartleaf Philodendron (Philodendron hederaceum)
• Arrowhead Plant (Syngonium podophyllum)
• Swiss Cheese Plant (Monstera adansonii)
• Teddy Bear Vine (Cyanotis kewensis)
• String of Pearls (Senecio rowleyanus)
• String of Nickels (Dischidia nummularia)
• Pothos (Epipremnum aureum)
• English Ivy (Hedera helix)

Note that depending on your location, not all of these might be available (I'm sure that all of them left to their own devices would become an invasive species).

Finally, it's not an either or situation, you can both move the lattice to a more favourable location (which would help the plants in the dark of winter) AND choose plants that grow better in indirect light conditions.

Answer 2

You would need a two mirror system for your setup. Ideally, you’d need your mirror to dim area ratio to be at least one to one, depending on how far the mirrors are placed. One small mirror won’t do much. Or, you’d need to use a convex mirror for the second one - the kind you sometimes see placed in areas where there’s a blind spot for traffic or corners of store ceilings to monitor for shoplifting.

If you’re okay with double mirror aesthetic, it might be easier to just get some supplemental LED grow lights and tastefully incorporate them above the lattice.

Answer 3

You need a sort of venetian-blind or jalousie with slats that are strips of mirror.

Because you will be redirecting the sunlight through such a small angle, the slats will need to be quite wide relative to the spaces between them.

I suggest starting with a venetian-blind set twice as high as the window. Take it apart, removing the strings and all the slats.

Cover each slat on one side with reflective mirror film. There are many brands and types of this film; you want cheap and stiff. You will probably not need glue to make the film stick to the slat. Just spray the slat with water and smooth with a squeegee.

Reassemble the blinds with new strings. The slats should be very close together, with the exact distance depending on the slat width and reflection angle. When the slats are at the proper angle to reflect the sunset onto the green wall, if you look at the slats from the center of the green, you should not be able to see outside between them.

This is a medium-advanced DIY project but the result will take up hardly any of the room's volume.