Is it possible to over-mulch your garden?
Like anything, moderation is good. As shown here before mulch volcanoes around the base of trees can actually prohibit the tree’s success. The same can be said if too much mulch is applied to a garden bed. When landscaping your garden the most mulch you would want to apply is 10-15cm (4-5in) of 
organic material and approximately 5cm (2in) of inorganic material.
In spring we will commence the annual mulching of our garden beds before the summer season arrives. This will aid in halting evaporation that removes the water from our plants that we pay so much for. I’m a big fan of mulch, not only for its purposes but also for its aesthetic qualities. It’s like putting a black background behind a photograph.
If you want to neaten your garden before you put it on the real estate market – mulch the beds. It makes an incredible difference. I’ve seen homeowners who have done this and instantly the house looks better.
So what types of mulch are there and what are their purposes?
The types of mulch are varied and can be anything organic or inorganic.
- Straw/Hay/Lucerne – These are great to put around fruit trees and look great in cottage gardens. They’re inexpensive materials and will keep down weeds very effectively. The best way to apply this type of mulch is to first put down some blood and bone fertiliser around the base of the tree. Overlay this with some newspaper to cover the spread of the tree and then cover the paper with sheep or horse manure (slow-release fertiliser). Finally apply the straw densely over the manure and water in.
- Manufactured Mulches – we’ve just applied some mushroom compost to our beds because of the ease of use and high manure levels within the mulch. Mulches purchased this way have a uniform colour, usually very dark, and can be easily spread across the garden beds. In our ornamental beds we applied some blood and bone before adding the mulch while we just applied the mulch (no fertiliser) to our native garden. The reason, Australian natives don’t mind some fertilising but not in abundance.
- Material Mulches – these mulches are used predominantly for aesthetic purposes. They may consist of broken coloured glass, pebbles, woodchips or any other material than can still allow water to seep in and yet minimise evaporation.
What are the purposes for laying mulch?
- Aesthetics – this may or may not be the biggest reason for your desire to mulch. It all depends on what you’re trying to achieve. You may be trying to create a particular feel to a landscape and these materials help convey that. It may be that you just want to neaten up your garden and are laying a backdrop for this.
- Feeding Your Garden – we usually purchase feeding mulches because we prefer to put these items onto the garden in the hope of improving soil quality. As these mulches break down further, they condition the soil and add to it.
- Keeping Weeds Down – this is a great strategy for using mulch and the reason why it should be applied generously. The heat and density of the mulch will slow down weeds from germinating and also being able to penetrate it. It also means that you shouldn’t put your mulch right up to the base of the plant as it is possible to kill them.
- Slows Evaporation – one of the big reasons you would mulch your garden is to stop evaporation. During the hottest months it’s quite possible to see more water being evaporated from your garden than you’re applying to it. Mulching will slow down this process and allow the plants to retain their required moisture.