Avoiding Possible Problems With Mulches

• Plants may develop nitrogen deficiency 

  • Use composted mulch materials with a C:N (Carbon:Nitrogen) ratio of 25:1 or less.​

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• Excessive moisture in fine-textured or poorly drained soils​

  • Apply treatments to improve drainage; use of mulch ​may not be appropriate.

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• Air temperatures in the winter are colder above a mulch​

  • Remove mulch before cold weather so the heat capacity of the soil can moderate air temperatures​

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• Air temperatures are hotter in summer above a mulch

  • Avoid using mulches where heat-sensitive plants could be damaged during high summer temperatures​

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• Mulched plants may be delayed in developing hardiness ​because they usually grow later into the summer

  • Remove mulch in late summer; this is not a common problem and has been reported only on species that were marginally ​hardy for the area (Whitcomb 1980)

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• Mulch may delay growth in spring because the soil warms more slowly than without mulch​

  • Remove mulch around plants to expose soil to sun in the spring; it is unusual that this would be a problem for woody plants​

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• Some diseases, such as collar rot and Armillaria root rot may be more likely​

  • Do not place mulch against the trunk and root collar​

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• Rodent damage to root collars and trunks may be increased​

  • Keep mulch away from the trunk and root collar will discourage rodent feeding because it removes their cover for activity​

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• Some mulches increase fire hazard​

  • Avoid using loose mulch of straw or other dry, lightweight materials where fire is of concern​

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• Some mulches may be phytotoxic​

  • Use mature composted mulch​