Compost and mulch are vital materials for a bumper harvest, but deciding which one to use depends on your soil's specific needs. Compost is ideal for improving soil structure and regulating soil pH. Mulching is ideal for a garden's aesthetic appeal, to prevent soil erosion, lock in soil moisture, and control weeds.
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What Is the Difference Between Compost and Mulch?
Compost, dark brown humus, is essentially decayed organic materials created through biodegradation.
The organic material includes organic yard waste, sawdust, paper products, grass clippings, and kitchen scraps and peels.
On the other hand, mulch can be any material put on the soil surface to prevent weed growth and erosion, and retain moisture. It could be wood chips, shredded tires, lawn clippings, pine needles, hay, geotextiles, cardboard, or peat moss.
| Compost | Mulch |
| Decomposed organic matter mixed into the soil | A layer of protective material spread to the soil surface |
| Contains many nutrients suitable for plant growth | Suitable for keeping moisture locked into the soil, controlling weeds, neutralizing soil temperature, and preventing erosion |
| Consists of organic materials only | There are organic and inorganic mulches |
| Compost can be used as mulch | Inorganic mulch cannot replace compost. However, organic mulches can be dug into the soil and become compost after undergoing the decomposition process. |
| Compost releases nutrients faster into the soil when used as mulch, especially during the rainy season | Takes time for mulch (organic) to decay and add nutrients into the soil. |
| Compost is soil amendment that looks and feels like soils | Mulch is shredded material in its natural or artificial form |
Can Compost Be Used as Mulch?
Absolutely! Compared to regular mulch, compost provides multiple benefits to your garden when spread on top of the soil.
Here are the benefits of using compost as mulch:
1. Improves Soil Structure
Soil is made of sand, clay, and silt. The combination of these particles is called soil structure.
The nature of these particles determines the soil’s ability to retain water, maintain good drainage, and resist erosion. The perfect way of improving how the particles aggregate or clump together is through compost.
Compost contains earthworms, fungi, and bacteria, among other microbes that scrawl through the soil, mixing it up and changing its structure.
They also produce a sticky substance that converts the particles into micro aggregates, thus improving the structure.
2. Promotes Plant Growth
Compost is packed with nutrients such as potassium, nitrogen, and phosphorus, crucial for plant growth. It naturally releases these nutrients slowly, providing the plants with food over a longer period.
As mentioned earlier, compost improves soil structure, maintains soil drainage, and prevents erosion. Good soil drainage means the soil can retain moisture for plant growth.
On the other hand, compost also holds together loose soil, preventing the nutrient-rich top layer from being washed away by rain or blown by the wind.
Additionally, soil with good structure is neither too loose nor too tight, so root penetration in search of water and food becomes more accessible.
3. Balances Soil PH
The optimum soil PH ranges between 6 and 7. When the pH is too low (acidic), it inhibits nutrient release such as phosphorous into the soil. On the other hand, a high ph level (alkaline) kills crucial microorganisms.
Once amended into the soil, compost acts as a buffer, neutralizes acids or bases in the soil, and maintains neutral pH levels.
How? Compost contains positively charged hydrogen ions that lower the pH once released into highly alkaline soils.
It also contains negatively charged ions that attach to the hydrogen ions to raise the pH levels of acidic soil.
When to Use Compost?
The ideal time to use compost is at the start of a growing season or when you anticipate the beginning of the next season. As mentioned earlier, compost is nutrient-dense and makes your soil healthier and ready for plant growth.
When using compost for your vegetable garden, mix about 3 inches of compost into the top 5 inches of your planting bed. Top-dress your garden bed with compost during the growing season if your plants have a higher nutritional need.
Use compost mulch when planting roses during winter. Add 6 to 9 inches of compost around the base of your roses as a protective layer.
You can also mix compost in your potting soil when planting starter plants. Mix the compost and pot soil in a 1:1 ratio.
When to Use Mulch?
Mulching requires perfect timing. You can add mulch during late winter or early spring.
- Add mulch in early spring if you live in a dry area. However, if winter is too wet, mulching mid or late spring is advisable to avoid slowing down the warming process or trapping too much moisture into the soil.
- If you struggle with aggressive weeds, add mulch in early spring.
- Add mulch during early winter if your soil has deficient nutrient levels.
- During freezing winter, adding a layer of mulch adds a warm blanket that prevents your plants from freezing.
Caution: Mulch should not come into direct contact with your trees and shrubs. Direct contact causes the stem to soften, exposing it to diseases.
Can You Add Compost on Top of Mulch?
It is not recommended to add compost on top of the mulch. Compost should always be in direct contact with the soil. When you put compost on top of mulch, three negative things happen;
- Compost nutrients will not be able to get their way through the mulch layer into the soil
- Nitrogen in compost will be burnt away once exposed to direct sunlight
- Weed seeds in compost will sprout first, denying your plant seeds vital nutrients
Can You Just Put Compost on Top of the Soil?
Absolutely yes. Adding a layer of compost on top of the soil has numerous benefits. The compost naturally finds its way into the soil, providing nutrients for plant growth. It also acts as a protective layer from erosion, direct sunlight, and weed growth.
Adding a layer of 2 to 4 inches of compost is recommended if your soil has a good soil structure. Digging and mixing compost with structural fit soil disturbs the delicate microbes, thus affecting their productivity.