Why the recommendation to maintain a 2″ layer of mulch? Wouldn a thin layer be just as attractive?
A. The 2″ thick mulch layer serves several purposes. First, it looks better than bare dirt. Second, it helps prevent compaction of the soil from pedestrians walking through the planters by distributing their weight over a larger area. Third, it reduces weed growth because many smaller weeds can’t grow up through the thick mulch layer. Fourth, it reduces water loss due to evaporation from the soil surface. Finally, it helps promote healthier plants. It does this by keeping the top 4″ of soil, where almost all of the shrub and tree feeder roots are, cooler in summer and warmer in winter. Mulch also encourages earthworms in the soil, which helps aerate the soil, reducing problems with root rot. Bark mulches also decompose into a product called humus, which assists in nutrient uptake by the roots. Thus, the need to add mulch each year to replace the mulch that decomposed is actually almost as important as fertilizing the landscape. (Note that with some desert plantings rock mulches are use
