Concern's fast acting weed killer kills weeds, algae and moss withing hours of applying.  Will not stain bricks, concrete or asphalt.  Concern Fast Acting Weed Killer can be used inside your orchid greenhouse to effectively eliminate all weeds. No mixing required, just spray.  Concern Insect Killing Soap is derived from Neem Oil which makes it a fast acting non-selective herbicide (weed killer).  Areas treated with this product can be sown five days after treatment.  Best results are obtained with young, actively growing weeds, less than 5" in size.