Compost, the result of decomposed organic matter, is a powerful soil amendment that improves water retention, soil structure, and nutrient availability in gardens and landscapes. The answer to whether you can purchase it is a resounding yes; commercially produced compost is widely available for all scales of gardening. Buying compost is often a practical solution when a gardener needs a large volume, lacks the time for home composting, or requires a specialized mix of ingredients. This convenience allows gardeners to immediately enrich their soil without the months-long process of building a finished product from scratch.
Where to Source Commercial Compost
For smaller projects, such as container gardening or small raised beds, bagged compost is the most convenient option, typically found at big box stores and local garden centers. While these retail packages are readily available, the quality can vary, and the cost per volume is significantly higher compared to bulk options.
Local nurseries and garden centers often supply specialized compost blends, offering a higher quality product and expert advice. For larger landscaping projects, buying in bulk is the most economical choice, with materials typically sold by the cubic yard by bulk suppliers, such as landscape yards. Bulk purchasing offers substantial cost savings, as one cubic yard can equate to roughly 27 standard retail bags.
Municipal composting programs process local yard waste and sometimes food scraps, often selling the finished product to residents at a reduced price or providing it for free. The nutrient content and consistency may fluctuate based on the local feedstock materials. When purchasing bulk, you will need a truck or must arrange for delivery from the supplier.
Understanding Different Types of Purchased Compost
Compost is categorized by its primary feedstock, and understanding the source material helps match the product to the gardening need. Yard waste compost, derived from leaves, grass clippings, and wood chips, is a common general-purpose soil amendment. This type is valued for improving soil structure and organic matter content, serving as a reliable foundation for most garden applications.
Manure-based compost (cow, horse, or poultry) is richer in nitrogen and other nutrients. While beneficial for heavy-feeding plants, it must be used carefully, as high-nutrient composts can be too strong for seedlings. Mushroom compost is a byproduct of the mushroom growing industry, often consisting of straw, hay, and gypsum, and is typically alkaline, making it suitable for neutralizing acidic soils.
Vermicompost, or worm castings, is the product of earthworms digesting organic matter and is highly concentrated in microbial life and nutrients. It is often sold in smaller quantities and used as a potent soil inoculant or supplement for potting mixes rather than a large-scale amendment. Many suppliers also offer specialized blends, which may combine different feedstocks or be screened to a fine texture for use in topdressing lawns or creating custom potting mixes.
Key Factors for Selecting High-Quality Compost
High-quality, finished compost indicates proper decomposition and maturity. The texture should be uniformly dark, crumbly, and resemble rich soil, with no recognizable pieces of the original feedstocks. Immature compost that is coarse or contains large, undecomposed wood chunks can draw nitrogen away from plants as it continues to break down in the soil.
The smell is an immediate indicator of quality; a finished product should have a pleasant, earthy aroma. A sour, acrid, or ammonia-like smell suggests the compost is anaerobic (lacked sufficient oxygen) and may contain compounds harmful to plant roots. An ammonia odor specifically indicates an excess of nitrogen being lost as a gas, which occurs when the initial carbon-to-nitrogen (C:N) ratio was too low.
The ideal C:N ratio for the composting process is around 25:1 to 30:1, while a finished product will have a ratio closer to 15:1 or 20:1. Purchasing compost with a Seal of Testing Assurance (STA) certification from the U.S. Composting Council provides assurance that the product has been tested for maturity, pH, soluble salts, and heavy metals. High levels of soluble salts, which are measured in lab reports, can cause dehydration of plant roots, making it necessary to leach the compost before use if the reading is too high.
Proper Application Methods for Purchased Compost
Once the right product is selected, there are several methods for incorporating purchased compost into your gardening routine.
- Soil amending involves mixing compost directly into the existing soil of new garden beds or raised beds, typically to a depth of six to ten inches. This physically improves soil structure by binding sandy particles and loosening heavy clay, while introducing organic matter and nutrients.
- Top dressing involves applying a thin layer (one-half to one inch thick) onto the surface of established beds or lawns. This surface application allows nutrients to slowly leach into the soil and acts as a fine mulch layer to suppress weeds and conserve moisture.
- Compost tea can be brewed for an immediate nutrient boost by steeping finished compost in dechlorinated water for 24 to 48 hours. The resulting liquid extract is rich in microorganisms and soluble nutrients. Apply this liquid as a soil drench or foliar spray, preferably in the early morning or late afternoon to prevent rapid evaporation.
- Screened, fine-textured compost can be used as a mulch alternative, providing a visually appealing and beneficial layer that slowly feeds the soil over time.