So I live in Phoenix, AZ in a house neighboring my grandparents. Today we had to cut down a huge pine tree in our front yard because it had died from bark beetle (or some other parasite). I mentioned that I would probably have to go to the store to get some bark mulch because my little flower garden used to be shaded by the big tree, and the added insulation for the soil might help it survive in the 100-degree summer. I just looked out my window, and my grandpa is shoveling sawdust onto my flower garden...without asking me or my husband. Is this good for flowers? I have simple ones, such as succulents, daisies, and lavender.
Its not really good for plants, especially if dug onto the soil, though not so bad a mulch, because it takes nitrogen from the soil as it breaks down. It's okay so long as you apply nitrogen to the soil beneath prior to spreading the sawdust, but obviously, that's not a choice you've been able to make. If you can scrape the worst of it off, then apply nitrogen, and replace the sawdust,that will lessen its nitrogen stealing effects. More info here https://www.gardeningknowhow.com/garden-how-to/mulch/using-sawdust-as-mulch.htm