It might sound scary, but nitrogen drawdown is just a temporary quirk and not a reason to stop using mulch. When you spread carbon rich mulches like wood chips or bark on top of soil, the microbes that break them down borrow nitrogen from the soil to fuel their needs. As a result, it can momentarily reduce nitrogen available to shallow rooted plants.
The good news is the effect is usually limited to the thin layer where mulch touches the soil and deeper roots remain unaffected, so established trees and shrubs are generally fine.
To keep everything happy:
- Where you grow shallow rooted plants and seedlings of flowers, vegetables and herbs, use a “fast to break down” variety like The Garden Family Sugar Cane Mulch or combine fresh woody mulch like The Garden Family Tea Tree Mulch with a nitrogen-rich layer (like compost or manure) underneath.
- After mulching, lightly feed with organic fertiliser or apply a fast-acting liquid fertiliser such as fish emulsion if you notice slow growth or yellowing leaves.
Mulch offers big benefits – moisture retention, weed suppression, cooler soil, improved soil structure – and with these simple tweaks, you can enjoy them without worrying about nitrogen.
For more background on how mulches work and how to manage nitrogen drawdown, read more about avoiding nitrogen drawdown when using mulch
Drawdown is only one part of using mulch well. The rest is timing and depth, which we cover in our guide to mulching garden beds.
