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Ornamental Bed

(March 2012)

QuestionI got mulch from the city this past week. It's beautiful this year but evidently toxic. I spent many hours today mulching. Later I walked around and looked at my beds and my tender perennials, lettuce and herbs, in addition to some flowering plants look like the leaves have burned. The mulch has a slight chemical smell. I can't imagine what that might be. Perhaps there is a chemical in the mulch or perhaps the mulch is very green and what I am smelling, and what is burning the plants, is excess nitrogen. What do you think would cause this problem and do you have any ideas what I can do? Should I water my beds excessively or put something on my beds to neutralize the nitrogen. Please let me know your thoughts. I'm frazzled, frustrated and worried about my plants.

AnswerThere sometimes can be a problem with what is called "Sour" mulch. What basically happens is that if the mulch pile is large and we get a heavy rain, the oxygen levels sort of bottom out in the pile when it gets waterlogged. Toxic gasses can begin to build up inside this anaerobic environment and if applied in this state, the mulch can burn or damage tender plants. If you are applying mulch and it has a rotten egg odor or ammonia smell, stop applying it. Turn the mulch pile, or spread it out to allow oxygen in. The condition in the mulch pile is quickly remedied, but if it has already damaged your plants, you may have to replace some of the more damaged plants. For more information on sour mulch look at our fact sheet at:

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