Is Mulch the Same as Compost? A Complete Guide to Using These Soil Amendments

Mulch and compost are two of the most important tools in a gardener’s toolbox But there is a lot of confusion about whether they are the same thing or not The short answer is no, mulch and compost are not the same. While both are organic materials that enrich the soil, they serve different purposes and are used in different ways. This article will provide a complete guide to understanding the key differences between mulch and compost, and how to use each one properly for a healthy, thriving garden.

What is Mulch?

Mulch refers to any material applied to the top layer of soil in a garden or landscape. The primary purpose of mulch is to suppress weed growth, regulate soil temperature, retain moisture, and prevent erosion. Mulches can be either organic or inorganic

Organic mulches are derived from plant materials and include

• Wood chips
• Shredded bark
• Leaves
• Straw
• Hay
• Compost

Inorganic mulches are not derived from plant materials and include stones, pebbles, plastic sheeting, landscape fabric, rubber, and other synthetic materials. Unlike organic mulches, inorganic varieties do not improve soil health by breaking down over time.

The benefits of mulching include:

• Prevents weed growth and seed germination by blocking sunlight
• Retains soil moisture by reducing evaporation
• Insulates soil and protects plant roots from extreme temperatures
• Reduces erosion by protecting bare soil from rain and wind
• Improves visual appeal and creates a finished look in garden beds

Proper mulching technique is to spread a 2-4 inch layer of mulch around plants, taking care to keep it a few inches away from plant stems and tree trunks. Mulch should be replenished annually as it decomposes.

What is Compost?

Compost is decomposed organic material made from plant-based kitchen and yard wastes. Through the natural process of decomposition, microorganisms in compost break down organic matter into humus, a nutritious, soil-like material.

Compost is created by combining yard trimmings like leaves and grass clippings with kitchen scraps such as vegetable peels, eggshells, and coffee grounds. This mixture is piled into a compost bin or heap, periodically turned for aeration, and allowed to break down into compost over a period of months.

The resulting compost is a dark, crumbly, earthy material, rich in nutrients and beneficial microbes. Unlike mulch, compost is designed to be dug down into the soil, rather than placed on the surface.

The benefits of compost include:

• Improves soil structure and texture
• Increases nutrient availability and fertilizes plants
• Promotes healthy root growth
• Increases moisture retention
• Encourages beneficial soil microorganisms
• Improves drainage in clay soils

Compost can be added to garden beds and plantings by mixing 1-3 inches into the top 6-12 inches of native soil. It is also commonly used to enrich potting mixes for container plants and seed starting.

The Key Differences Between Mulch and Compost

Now that we’ve defined mulch and compost individually, let’s summarize the key differences:

Location

• Mulch is applied to the soil surface
• Compost is dug into and incorporated with soil

Purpose

• Mulch protects and insulates the soil surface
• Compost nourishes plants by improving soil fertility

Composition

• Mulch can be organic or inorganic

• Compost is 100% decomposed organic matter

Consistency

• Mulch exists as loose particles of various sizes

• Compost has a crumbly, soil-like texture

Decomposition

• Mulch decomposes slowly over seasons or years

• Compost is already fully decomposed

Nutrient Content

• Mulch has low to moderate nutrient content

• Compost is rich in all essential nutrients

Application Frequency

• Mulch is applied annually or as needed

• Compost is added every 2-3 years

Using Mulch and Compost Together

Now that you understand the distinct roles of mulch and compost, it should be clear that using them together is ideal for a healthy garden.

Here is an effective way to use both mulch and compost:

1. Spread 1-2 inches of finished compost over the soil surface and mix into the top 6 inches of native soil. Compost is best worked into beds before planting.

2. Plant flowers, vegetables, shrubs and trees into the enriched soil.

3. After plants are established, apply a 2-4 inch layer of organic mulch around plants. Leave a gap between mulch and plant stems.

4. Reapply compost annually by topdressing beds with 1/2 to 1 inch of fresh material. Mix lightly into surface soil.

5. Replenish mulch as needed, generally on an annual basis.

Using compost provides nutrients and organic matter to feed plants from the roots up. A proper layer of mulch seals in that nutrition while suppressing weeds and regulating temperature and moisture at the soil surface. It’s a powerful one-two punch to grow thriving plants!

Mulch and compost are two of the most useful amendments for building fertile, healthy garden soil. While they are both organic matter, mulch is applied on top of soil and compost is worked into soil. Learning when and how to use each one according to their different strengths will lead to better results in your garden.

Mulch primarily protects and insulates the soil surface, while compost nourishes plants by improving soil texture, fertility and microbial life underground. An effective gardening practice is to work compost into beds, then mulch generously around plants to maximize the benefits. With this complete understanding of the purposes and ideal uses for mulch and compost, you are equipped with the knowledge to build soils and grow gardens sustainably using natural organic methods.