Great information. Thank you!Perfect timing for this question. I heard a podcast about this so I checked out the study. Any leaf that is not receiving at least 200 ųmols of light won’t perform photosynthesis. It will continue to transpire though. So essentially you have leaves that are sucking up nutrients, and spitting out humidity, but aren’t doing anything for the grow itself, yet.
Now, this gets a bit tricky. Those leaves that aren’t photosynthesizing aren’t necessarily a bad thing. They’re holding a whole bunch of nutrients the plant can call on when it needs more. This is useful deep into flower. However, there’s a line to watch. If your airflow is poor and/or humidity is an issue, it may be more beneficial to trim off anything below 200 ųmols.
Outdoors this isn’t really an issue. The sun will hit any leaf that is exposed to it. Indoors though, with a beefy canopy, a lot of that light won’t penetrate to the container level. If you’re an organic grower, you will likely want to keep as many leaves as possible even if they aren’t photosynthesizing. If you’re using mineral salts, keeping nutrient sinks aren’t as important since you can just dose the plant with whatever it needs when it needs it.
This info gives the grower a standard and a measurement they can use to determine which leaves to take and which to keep instead of guessing.