I have a terrarium with some small cactuses in it. Small as in smaller than the 10 inch or so clear plastic walls.  My question is, does the sunlight they need have to be direct or can it be through the clear plastic?

Some of my grandfather’s greenhouses were plastic, as far as I can remember. I can’t imagine it makes much difference, except for the light not being as strong.

I’m pretty sure plastic and glass only absorb certain UV wavelengths but let most visible light through. I don’t know anything about cacti but most plants rely on visible light wave lengths ( except green) for photosynthesis and don’t use UV at all, so if it is filtered out by the plastic it shouldn’t matter.

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Unless they get sunlight for most of the day you may want to supplement it with a small fluorescent gro-light (historically very popular with in-door pot growers).  They make covers with a light socket, that fit over aquaria or terraria.  (Oh, geez, George is going to attack my approach to pluralizing these.    )

Occam

Great info guys, thanks!

My gf and I have 5 or 6 cacti and through the winter we just sit them by the big window and they seem to do fine.  Hell, one of them, who we’ve named Juan, we call the Highlander Cactus because he just keeps growing and no matter what happens to him he survives and thrives.  Freaky ass super-cactus.

I think the rays can still penetrate but better if it the plant directly receives it..

I recall, as a small child in New England, my mother carefully nurturing some geraniums through the winter she had in pots by a south facing window.  When we came to Calif, they were growing everywhere almost like weeds.

Occam