I wouldn't use that type of bark. Plants could find certain bacteria useful while your reptile could suffer with these bacteria.

However I find that the absolute best substrate for a snake would be eco-carpet. It looks relatively nice and is insanely easy to clean. It can be just rinsed, soaked or even put on a rinse cycle in the washing machine. It can be used for years and years before it needs replacing. It makes it easier to clean and is easier on the wallet. It isn't as ugly as paper towels or newspaper either. It really is the best.

When I first started keeping snakes I used reptile bark and it seemed fine. That was until I got a mite infestation. It was absolutely impossible to get rid of with the bark (even after complete substrate changes and bleach cleanings) but it cleared up right away with the eco-carpet. Also if you feed your snake in its cage it could cause digestive problems when using bark.

the reptile bark s safest for the snake. nursery bark will quite possible have some undesirable characteristics that could be harmful to the snake.

Don't feed your snake in its tank so you dont have to worry about that. If it is pesticide and herbicide free, then it is safe as long as you bake it in the oven for an hour or so. This will kill any bacteria and parasites.

It should be fine. I'd make sure that it doesn't contain any fertilizers though before use.