In the previous post we looked at some of the benefits of mulching. This time we will examine some of the things you need to consider when choosing which mulch to spread over your garden beds.
Firstly, if we look at nature we can gain some insight into the importance of mulch and it's composition in the natural environment. In dense bushland/forest areas, mulch is created naturally by pieces of bark, fallen leaves, twigs & branches that fall from the forest canopy and build up on the ground. This is why in those areas you'll always find a thick layer of organic material on top of the soil, keeping the soil moist and supressing weed germination. At the lowest layer of this organic material, the area where humus interacts with the soil surface, soil microbes and worms are continually breaking this organic matter down into a form that plants can use and mixing it into the soil.
What does all this mean to us in an urban environment? Firstly, the closest type of mulch to approximate the compostion of mulch in natural areas is the relatively cheap and sometimes free mulch available from your local tree lopper (or from me if I lop & prune your trees). Similar to the mulch in those natural environments it contains leaves, twigs, bark & chopped up branches. It's generally fairly chunky in its consistency which is important because it allows water to percolate through to the soil surrounding the roots of your plants. Another good choice is pine bark mulch which retains it's colour for a long period of time & has the added benefit of slightly acidifying the soil, which counteracts the effects of the mostly alkaline soils in Perth.
By contrast, fine particle mulches quite often pack down tightly over time, holding moisture above the soil layer forcing your plants roots upwards searching for that moisture. It also contributes to faster evaporation because that moisture is held in a layer closer to the drying effects of wind and sun.
The next post will be the last in this series on mulch and will deal with a prominent myth about using fresh woodchips. Does it tie up nitrogen or not?