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What are the effects of road base and deco (inorganic mulches) on plant health?

A friend wants to put inorganic mulch up to the base of the tree, however, I don't think its a good idea. I am concerned about pH and making soil anaerobic. 

General Advice • Garden Jobs

When it comes to choosing a mulch for plants, generally, an organic mulch - as opposed to an inorganic mulch - is best for plant health.


Organic mulches

- Examples of organic mulches include wood chips, sugar cane, pea straw, bark, etc.

- Advantages of organic mulches include: weed suppression; cooler and protected surface roots; once the mulch breaks down, it adds soil organic matter - improves soil structure, adds air, nutrients and food for soil organisms; helps retain soil moisture; and prevents soil water repellency (hydrophobia). 

- Disadvantage: some organic mulches can cause an effect known as "nitrogen drawdown", however, this is easily fixed by first applying a fertiliser such as Yates Dynamic Lifter Soil Improver & Plant Fertiliser


Inorganic mulches

- Examples include blue metal, pebbles, stones, granite, etc.

- Advantages include: aesthetically pleasing, and some weed suppression.

- Disadvantages include: increases soil surface temperature (hot roots); soil compaction (which can cause soils to become anaerobic); prevents organic matter from entering the soil; and doesn’t feed the soil or soil organisms.  

- A tip when applying inorganic mulches, it is best to first lay down weed mat, then apply the inorganic mulch. This will help to prevent the inorganic mulch from being embedded and mixed into the soil, and will also allow you to remove, wash, clean and refresh the area when it needs it.

- Plants that tolerate inorganic mulches include Grass trees, grasses (e.g. lomandra, and Pennisetum), and sometimes cacti and succulents





Answered: 9 Apr, 2021

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