All of the plants in all the beds did not grow as they did in past years. Someone pointed out that walnut stunts the growth. Would this be the case of the dark black mulch? I used dark black mulch last year and I had a very poor showing of flowers. The retailer claimed there were NO walnuts in the mulch.
Would Dark Mulch Have Walnuts Inhibiting Growth?
Certified GKH Gardening Expert
It would not have contained black walnut. But, if you use mulch every year, the soil may be depleted of nitrogen, which would stunt plant growth. You should have the soil tested to see if this has happened.
Another possibility is that the mulch was dyed, which has its own issues. This article has more on that: