Gardeners, landscapers, and farmers grow two things: plants and soil. Building healthy soil that teems with life is fundamental for growing healthy plants, fruits, and vegetables. Compost and mulch are versatile tools for improving soil health in gardens, and StopWaste can help you get the most out of these amendments.

Amending Soil with Compost

Compost is not soil, despite the visual similarity! Compost is an amendment applied to soil to provide physical and biological benefits to soil and plants, and is made of well-decomposed and stabilized organic matter from the aerobic decomposition of plants and food scraps.

In the soil ecosystem, organic matter is the primary food and energy source for the beneficial fungi, bacteria, and invertebrates maintaining the soil food web and providing many ecological functions to the soil. Using compost essentially feeds the soil ecosystem, which cascades into various benefits. Compost boosts soil fertility, enhances soil structure, improves moisture retention and drainage, assists plant roots with accessing nutrients, and feeds soil microbiology responsible for nutrient recycling and exchange with root systems.

While compost is a versatile and forgiving soil amendment to use, it's important to know how to use it properly.

General Guidance for Using Compost

  • Establishing new garden beds: Mix 2-4 inches of compost into the top 6-8 inches of soil before planting. For heavier clay soils, 4-6 inches of compost can be used. StopWaste generally advocates for no-or-low tilling of soil, but there are benefits to incorporating compost into top 6-8 inches of soil when establishing new garden beds.
  • Top-dressing existing garden beds: Apply a 1/2 - 2 inch layer of compost over garden beds. Water into the soil, as opposed to incorporating into the soil through tilling.
  • Top-dressing on lawns: Spread a thin 1/4 to 1/2 inch layer of fine compost over established lawns or garden beds. Immediately irrigate to help compost particles wash off grass blades and enter the soil.
  • Potting and seedling mixes: Sift compost through a 1/2 or 1/4 inch mesh screen. Blend 1 part sifted compost with 3 parts potting soil. You can add other ingredients to create custom growing media for containers and raised beds.
  • Compost tea, extracts and dilutions: In a 5-gallon bucket, toss in 1-2 handfuls of compost and fill with water, mixing along the way. Once thoroughly mixed, it can be immediately used as a compost dilution or extract for soil drenching. To brew a compost tea, you can continue to mix the compost-water and add aeration using a compost tea kit or bubbler. Compost tea builds the microorganism population, and after 1 hour of aeration, can be sprayed for foliar feeding or used for soil drenching.

Using Mulch

Mulch mimics the natural layer of fallen leaves and organic debris that protects and builds the soil in forests and meadows.

  • Apply 3-4 inches of organic mulch (wood chips, shredded bark, or straw) around plants, keeping mulch a few inches away from stems and trunks.
  • Replenish annually as mulch decomposes and incorporates into the soil over time.
  • Use coarser materials (wood chips) for pathways and around trees; finer materials for garden beds.

Benefits of Compost and Mulch

  • Improve soil structure: Quality compost teems with microorganisms — one teaspoon can contain more than one billion beneficial microbes
  • Retain moisture: Compost improves the water-holding capacity of soil; mulch reduces evaporation
  • Address problem soils: Compost helps with compacted earth, heavy clay, sandy conditions, nutrient-poor soil, and even lead-contaminated areas
  • Suppress weeds: A thick mulch layer significantly reduces weed growth
  • Regulate temperature: Mulch insulates soil from temperature extremes

Compost and Mulch Together

For best results, apply compost to the soil first, then cover with a layer of mulch. This combination feeds the soil ecosystem from below while protecting it from above.

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