In the SCV, typically we look to improve drainage and aeration within the landscaping. An organic soil amendment can improve drainage and aeration while also providing nutrients and beneficial organism habitat. Most often, soil amendments are incorporated into the soil at planting. They can also be incorporated outside of the plant’s root zone during routine cultivation.
Although many gardeners frequently think manure is the ideal amendment, in most cases, your neighbors will thank you (and so will your landscaping) if you avoid it! It has a lot of salt and can contain weed seeds. Lots and lots of weed seeds.
A mulch has the same basic characteristics as a soil amendment, but instead of being incorporated into the soil, it is placed on top in a layer 2” to 4” thick. Although non-organic materials like gravel, stone, or decomposed granite can be used as mulch, they retain a lot of heat in the summer months, and don’t provide any nutrients to the plants. We see a lot of projects with rocks proposed – please think of the heat. That is truly a hard place for plants to survive.
Organic mulch (the chunkier the better!) holds in soil moisture, helps to keep the soil cooler in the summer months (reducing water loss from evaporation) and helps to keep the soil warmer in the winter months. It is critical to keep the mulch at least 6” away from the base of the plants (the larger the plant, the farther away – up to 18” on mature trees and shrubs). Piling mulch against the base of plants will, over time, lead to disease issues and usually death. Other benefits of mulch include reduced soil compaction, reduced weed growth and reduced water runoff. It is important to re-apply mulch as needed; it needs to be an on-going cultural practice.
Mulch needs to be replenished as it breaks down over time. If applied correctly it should only need to be reapplied 1 or 2 times per year.