As far as I understand, Cedar is not aleopathic (as other species like
Black Walnut are), but rather pest & rot-resistant. This makes Cedar particularly good at raised beds & other outdoor structures (since they will resist rot for much longer than other woods) and particularly bad at Hugelkultur (since the
pests and rot are what transform the buried wood into nutrients for plants). There
should be no ill side-effects to growing in Cedar raised beds — it's possibly the best wood you could choose!
Here's a quote from a
short summary from the WSU extension:
Cedars, especially Thuja species, have developed chemical weapons against a number of pests and pathogens. Researchers have found that Thuja plicata heartwood contains thujaplicin, a water-soluble tropolone not only inhibitory to various bacteria and fungi, but with anti-tumor activity as well. This antimicrobial activity is probably responsible for the rot-resistant nature of cedar wood. There is, however, no evidence that this substance harms plant tissues.
I always take a
common sense approach to toxicity. Every plant is toxic to something, this is the nature of our world. Peppers are toxic to us, but we happily eat them. The variables involved are too numerous to say something is always bad or always good. If you don't see a problem, there probably isn't one. If there is a problem, it's probably more obvious (read: human in nature) than you'd expect. Humans are way better at creating aleopathic compounds than nature could ever be.
As an example: When using wood chips, remember that tree service companies are generally removing unwanted
trees (ex: when they get in the way of power lines). Power companies don't want any trees near those lines. So they routinely
spray herbicides in the same areas they're removing trees. Maybe those cedar wood chips are reducing microbial activity... or maybe they're covered in herbicides. Evidence is slim that Cedar wood chips have negative effects on plants, but evidence is pretty strong that herbicides kill plants.