Your interior light levels form the growth potential of the plant. Your care efforts realize that potential (watering, fertilizing, repotting). Good light is the PREREQUISITE for a plant to grow but the term “bright indirect light” fails to convey anything concrete. At worse, it makes you think just any place the sun doesn’t shine is considered indirect light. And our eyes adjust to a wide range of light levels so you will NOT feel the difference. Instead, those with huge, unobstructed windows and/or skylights are patting themselves on the back at how good they are with houseplants while those with smaller windows living between buildings are struggling to figure out why their fiddle leaf fig always ends up with 90% of their foliage lost.
Measure your light. It will explain the magic of the greenthumb.
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Step 1: Get a light meter and get to know how bright your indirect light actually is. Here are a few that I think work well:
This is the Dr. Meter LX1330B Light Meter that I’ve been using – pricing has been varying wildly on Amazon but it should be around $40-60 [US Link] [CAN Link]. An alternate model: [US Link] [CAN Link]
The Urceri light meter also works well and has the advantage of automatic range selection. The only downside is the sensor cannot be pointed away from the screen so you may need to use the ‘hold’ function (should also be around $40-60) [US Link] [CAN Link]
What about apps? Android devices do not have standardized ambient light sensor hardware and the iOS platform doesn’t give access to the iPhone light sensor, which means those apps are doing a rough calculation based on the camera brightness value. An app might be able to give you a rough idea, but a dedicated device will do the proper cosine correction for the angle of incident light (that’s what the white dome is for).
Step 2: Bookmark this page so you can look up the levels of indirect light necessary for various plants. I don’t have every possible houseplant but after reading a few of these, I think you’ll get the idea.
Commercial Light Levels: most of our typical “houseplants” are grown in greenhouses with varying layers of shade cloth. To give you a rough idea, “50% Shade” would measure to 5000 foot-candles (FC) and “90% Shade” comes to 1000 FC – this is the strength of the sun shining through different layers of shade cloth, which is a black net-like material. These numbers are easily searchable on the internet – I’ve included the source links where applicable. *Don’t expect to achieve these light levels indoors from your indirect light.*
Interior Light Levels: plants can technically survive in a wide range of light levels so do not take the numbers listed here as prescriptive – they aren’t strict requirements. You should think of them as guidelines for good growth. Another consideration is that “good growth” is subjective as any plant will take the shape of its light situation – up to a certain point, it’s not entirely under your control! These numbers are gathered from my own observations and measurements. *Use these as guidelines.*
How to measure: from the spot where your plant is sitting, while the sun is NOT in view, you want the measurement to be above the “good growth” foot-candle reading. Measure at different times of the day and in different weather conditions so you can get a sense for the average intensity of your indirect light. When the sun IS in view, you want the duration to be less than what is stated as tolerable – and if the sun will be in view for longer, then block it with a white sheer curtain.
Adenium Plant
Aglaonema Plant
Ajwain Plant
Allamanda Bail
ALOCASIA PLANT
Aloe Vera
Aloo Bukhara Plant
Anar Plant
Apricot Plant
Areca Palm
ASPARAGUS PLANT
