A person wearing blue and gray work gloves holds a cupped handful of reddish-brown wood mulch.

Mulches & Soils

Whether you're planning a new garden bed or maintaining a mature landscape, our FAQs have the answers to common questions. Learn the right techniques for applying mulches and soil to ensure a healthy, thriving foundation for your lawn and garden.

Mulch & Soil FAQs

What is growing in my bag of mulch or soil?

Why do I sometimes find mold or fungus growing inside a sealed bag of soil or mulch?

If you open a new bag of soil or mulch and find white mold or fungal spots, it's a direct result of moisture content. Mold and fungus thrive in moist environments containing organic matter. Since soil and mulch bags are not always perfectly waterproof, water content from the original packaging (especially in colored mulch, which retains moisture from the dyeing process) or moisture seeping in after packaging provides the ideal conditions for these harmless organisms to develop.

The mold and fungus found in soil or mulch bags are generally harmless. They are natural organisms that help break down organic matter and contribute to the health of your garden, rather than damaging your plants. They pose no risk to people or pets, though wearing gloves when gardening is always a good idea.

If you see mold on the exterior of a bag of soil or mulch, do not purchase it. This may indicate improper storage conditions and potential contamination. Unlike mold found inside the bag (which is often harmless), external mold suggests a compromised product.

Fungi, including mold and mushrooms, are essential components of a healthy soil ecosystem. These beneficial microorganisms perform a vital function: they break down organic material into readily available nutrients that your plants can easily absorb. This process is so crucial that we deliberately choose not to sterilize our growing media, ensuring we preserve these natural helpers that enrich the soil and foster balanced conditions for robust plant roots.

If you notice a large, unattractive amount of mold, it's typically a sign that the soil or mulch is too wet. While this overgrowth is not harmful to your plants, you can easily reduce or eliminate it by exposing the media to sunlight and air.

  • For Unused Soil/Mulch: Spread the product out on sheets of newspaper or a tarp and allow it to dry out before application.
  • For Soil/Mulch that is already applied: Allow the area in your garden to dry out a bit by reducing the frequency of your watering.

The mold should naturally dissipate once the moisture level decreases. Remember to always wear gloves when handling any growing media product.

How Does Mulching Help?

It Adds Curb Appeal

Mulch is the key to achieving a finished, professional look in your yard. It immediately adds rich color and texture to areas like landscape beds, around trees and shrubs, or along your home's foundation. Choosing a colored mulch offers the added benefit of beautifully accenting and harmonizing with the existing colors of your home and flower gardens.

Mulches made from wood and other organic materials are valuable because they actively improve the soil as they decompose. Over time, natural soil inhabitants like microbes and insects consume the mulch. The by-products of this natural consumption are released back into the soil as organic matter, leading to healthier, more fertile growing conditions.

Mulch functions as an effective insulator, playing a critical role in regulating soil temperature throughout the year. It keeps plant roots cool during the heat of summer and provides essential warmth and protection during the winter months. This insulating property is particularly vital for tender, new plantings established in the fall, offering necessary defense as temperatures begin to drop dramatically.

Mulching directly contributes to reduced watering time because it acts as a barrier to moisture evaporation. By slowing down this process, mulch ensures that more water remains conserved in the soil, readily available to nourish thirsty plant roots.

Applying a 2 to 3-inch layer of mulch provides a natural, effective barrier against weeds. This works by blocking sunlight and physically suppressing growth, which prevents weed seeds from sprouting and taking over your landscape beds.

How much mulch do I need?

A table titled "Help with calculating the number of 42.5 liter bags of mulch" shows the required number of bags for coverage at two different depths: 5 centimeters (2 inches) and 7.5 centimeters (3 inches). The table indicates that an area of 2.2 square meters (24 square feet) requires 3 bags at a 5 centimeter depth or 4 bags at a 7.5 centimeter depth; 4.5 square meters (48 square feet) requires 6 bags or 8 bags; 6.7 square meters (72 square feet) requires 8 bags or 12 bags; and 8.9 square meters (96 square feet) requires 11 bags or 16 bags, respectively.
Area Number of 42.5L bags at 5 cm (2") Depth Number of 42.5 L bags at 7.5 cm (3') Depth

2.2 m² (24ft²)

3

4

4.5 m² (48ft²)

6

8

6.7 m² (72ft²)

8

12

8.9 m² (96ft²)

11

16

Application Tips for Mulch

Should I remove old mulch before applying new mulch?

In most situations, there is no need to remove old mulch since it will naturally decompose and enrich your soil. The only time removal is necessary is if the layer is excessively thick (over 4 inches). If you choose to leave the old mulch, always be sure to loosen it up before adding a new layer. This simple step is vital for improving both drainage and airflow in the soil beneath.

As a general rule, applying fresh mulch to your landscape or garden beds once a year is recommended.

What can I grow in a raised bed garden?

What grows well in a 15 cm (6") high raised bed?

Arugula, leeks, lettuce, onions, radishes, spinach, strawberries, basil, chives, cilantro, dill, mint, oregano, parsley, thyme, marigolds and other annual flowers

Beans, beets, broccoli, Brussels sprouts, cabbage, cantaloupe, carrots, cauliflower, collards, cucumbers, garlic, kale, summer squash, Swiss chard, turnips, lavender, rosemary, sage, borage, calendula, cosmos, lantana, nasturtiums, snapdragons, sweet alyssum (plus everything in the 6" list)

Artichokes, asparagus, eggplant, okra, parsnips, peppers, sweet potatoes, tomatoes, watermelon, winter squash, pineapple sage (plus everything in the 6" and 12" lists)

Feed your plants, one month after planting, with Miracle-Gro® Shake 'N Feed® All Purpose Plant Food 12-4-8, following label instructions. Using this plant food in combination with Miracle-Gro® Raised Bed Soil yields bountiful results. For the next growing season, you don't have to replace all the soil that has naturally broken down. Instead, simply refresh the old soil before planting by adding Miracle-Gro® Garden Soil All Purpose as directed on the package.

How much soil does your garden need?

A table answers the question, "How much soil does your garden need?" The table lists the Area Surface in square meters and square feet, and the corresponding Number of Bags Required for two different scenarios: 7.5 centimeters (3 inches) depth and 15 centimeters (6 inches) raised beds. For an area of 2.2 square meters (24 square feet), 6 bags are required for either depth. For 6.7 square meters (72 square feet), 12 bags are required for either depth. For 8.9 square meters (96 square feet), 24 bags are required for either depth.
Area Surface Number of Bags Required at 7.5 cm (3") Depth Number of Bags Required 15 cm (6") Raised Bed

2.2 m² (24ft²)

6

6

6.7 m² (72ft²)

12

12

8.9 m² (96ft²)

24

24