What is the white powder on some pieces of bark?Updated 4 months ago

This is dolomite (calcium magnesium), added to the bark in the final stages of production. It is beneficial for your plant, so do not wash it off if you see it! In rare conditions, fungi may grow on the bark, either before shipping or if the product is left in warm, moist conditions in your home. This can result in a fine whitish-gray layer of fungi on the bark. These fungi are most likely Penicillium or Paecilomyces and are not harmful to your plants; in fact, they can be beneficial by helping to prevent the colonization of pathogenic fungi. Typically, when the material is moved or shifted, the fungi are disturbed and will disappear.