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GUEST COLUMNIST: Love Your Yard and Eat It, Too! Compost is Compost is Compost – Or is it?

By Ari Tenenbaum.

Spring is just around the corner, and San Diego gardeners should be thinking about transitioning to warm season veggies like tomatoes, squash, and peppers. If you have spent the cool months harvesting greens and other winter vegetables, your garden soil is going to need some amendments before moving into the warm season. One of the best ways to recharge your soil is by adding compost. What many people do not realize is that compost is a very general term for decomposed organic material. An array of different “compost” products can be purchased from nurseries and green waste facilities, but it is important for gardeners to understand that not all compost is created equal. Learning how to evaluate different products will help you find the compost that is most suitable to your needs.There are three characteristics that I always look at when evaluating the quality of a compost product: Smell, texture, and source material.

  1. Smell: A high-quality, finished (fully decomposed) compost should have the sweet, earthy smell of a forest floor. Compost that is actively decomposing often has a sour, somewhat astringent odor due to volatile chemicals like ammonia that are released as a byproduct of the decomposition process. Anyone who has visited the Miramar Greenery may recognize the smell of the compost being produced there. The sour smell is a good indication that the compost is not fully mature. Care must be taken when amending soils with unfinished compost products. These products are not necessarily bad for your garden, but it’s best to incorporate them into your soil least least three to four weeks before you plan to plant.

  2. Texture: Compost for vegetable gardens should be finely textured. Avoid products with large chunks of woody material. Mixing woody material into a garden bed can tie up nutrients like nitrogen, making it unavailable for your plants. If you have compost with larger pieces in it, one option is to sift out the large pieces before adding it to your garden beds. The larger pieces can then be used as a surface mulch around shrubs and trees.

  3. Source Material: Nearly any organic material can be turned into compost, but some materials will provide significantly more nutrition for plants than others. For thousands of years, animal manures have been used to increase soil fertility. Compost that contains animal manures can be highly beneficial to gardens but it is essential that these products be fully decomposed. It is common to age manures for six months or more to ensure they are safe for use in the garden. Composts from green waste recycling facilities are typically composed of yard waste only. This eliminates any concern for pathogens like E. coli or Salmonella, but composts made from recycled green waste tend to have more woody material and fewer nutrients immediately available for plants.

There are a number of factors that may affect what type of compost you ultimately end up using to improve your garden soil. In the end, adding compost to your garden is generally going to be beneficial. The important thing is to understand how to get the most out of whichever product you are using. Compost from green waste recycling facilities is very cost effective, but it works best when incorporated weeks before you wish to plant. Alternatively, some bagged products and manure based composts may be significantly more expensive, but can be incorporated into garden soil and planted immediately. Like all things gardening, there is no right choice when it comes to compost. The best approach is to try some different options and figure out what works best for you.

Ari Tenenbaum holds a B.S. in Plant Science from UCSC and is a landscape designer and contractor in San Diego. His company, Revolution Landscape, specializes in the design and installation of edible and eco-friendly landscapes.

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