Mulch

Mulching is a simple yet powerful tool for gardeners and landscapers. By applying mulch properly, you can enhance the health and appearance of your plants, reduce water use, and even improve the quality of your soil over time. Whether you prefer the nutrient-boosting benefits of organic mulches or the long-lasting appeal of inorganic options, mulch is a valuable addition to any landscape.

Why use mulch?

Mulch offers a variety of sustainable benefits to your landscaping, including:

helps prevent the germination and growth of weeds by blocking sunlight, making it harder for weeds to sprout.
reduces water evaporation from the soil, allowing plants to stay hydrated longer between watering sessions.
organic mulches increase the nutrient content of underlying soils.
acts as an insulator, keeping the soil cooler in summer and warmer during colder months, which can protect plants from extreme temperatures.
helps protect the soil from being washed away during heavy rains.

Types of mulch

Mulches can be composed of anything that is suitable as soil covering for landscape use. There are two main types of mulch: organic and inorganic, each with its own benefits and considerations.

Organic Mulch	Inorganic Mulch
Wood chips & shredded bark Long-lasting and provide excellent weed control and moisture retention. As they decompose, they slowly release nutrients into the soil.	Rocks, gravel, & stones Provides long-lasting coverage and are great for decorative purposes. However, they don’t improve the soil as organic mulches do and can heat up, potentially harming plant roots.
Compost Rich in nutrients, compost improves soil structure and fertility, but it may need to be applied more frequently and doesn’t offer as much weed control as wood chips.	Rubber mulch Made from recycled tires, this durable option is good for playgrounds but does not contribute to soil health and may not provide the same weed suppression as organic materials.
Fresh tree trimmings Offers good weed control and add nutrients to the soil, but they need to be replenished annually.
Grass clippings or leaves Great for adding organic matter to the soil, but can sometimes compact and reduce water flow into the soil.

How to apply mulch

To see the benefits of mulching, it’s important to apply it correctly. Proper mulching not only maximizes the benefits like moisture retention and weed control but also ensures the health of your plants. Incorrect mulching techniques can lead to problems such as plant rot, poor water penetration, and ineffective weed suppression.

Follow these guidelines to make sure your mulch works effectively and keeps your landscape looking its best.

apply freshly chipped mulch containing wood and leaves
use coarse mulch, greater than 1-inch in size
use on-site landscape trimmings, especially from trees
apply 6 to 12 inches of fresh mulch for ideal for weed suppression and moisture retention
do not pile mulch directly against the stems of plants or tree trunks, as this can trap moisture and lead to rot or disease
do not apply compost as mulch
if mulching on a slope, use shredded or coarse mulch to help it stay in place

References:

Mulches for Landscapes, UC ANR publication 8672 (Downer, J. and Faber, B. 2019)
California Master Gardener Handbook, UC ANR publications 3382 (Pittenger, D. 2015)