What Is Sour Mulch

Sour mulch occurs when the materials used to make mulch are stored in piles that are too large. These large piles can result in pockets of mulch near the center of the pile experiencing anaerobic conditions, or a lack of oxygen.

How do you fix sour mulch?

Once mulch has soured, the problem may be corrected by spreading it out in a shallow layer and watering heavily to leach toxic chemicals (Rakow, 1992). Adding large amounts of limestone will neutralize acidity and restore the mulch to useable form.

How can you tell if mulch is bad?

If your mulch has gone sour, it will smell like rotten eggs or vinegar. The best way to fix this is by spreading it out to dry. Turn the pile frequently and let the sun and air cook out the toxins. Using the mulch without cleaning it up can cause plant problems.