Compost is not something new to most plant growers using substrate (growth media) that contains organic matters. However, it has become a hot topic in recent years as we face more and more economic and environmental challenges, such as the continuous acquisition of growing substrate for each production cycle of ornamental crops like house plants in our area and the reduction of landfills with organic wastes.

Miami-Dade County ranks first in Florida and the United States at the county level in the production of ornamental crops, with sales of more than $946 million in 2022. Due to the majority of ornamental crops being grown in containers, growing substrates are sold with plants. Growers are searching for cost-effective solutions in producing growing substrates. One alternative solution that can be added to the growing media for ornamental crops is compost.

Compost with materials used to go to landfills has been used as ingredients of commercial potting mix. According to a recent report in the Miami Herald, organic wastes, including food wastes, plant materials, and paper, make up about 50% of the waste going to landfills nationwide. In our area, plant materials collected through landscaping and household waste are even more significant. Such organic materials can go to compost and recycle resources.

So, what is compost? Compost is the end product of a controlled, aerobic process (oxygen needed) that converts organic materials into a nutrient-rich, biologically-stable soil amendment or mulch through natural decomposition (www.epa.gov/recycle/composting; www.compostingcouncil.org/page/CompostDefinition). Although compost contains certain nutrients, it is not appropriate to market it as fertilizer, according to information from a recent meeting on compost held at the University of Florida GCREC. Instead of being used as fertilizer, compost can be mixed into the soil to improve the structure and health of the soil, help the soil retain moisture and nutrients, and reduce the potential for soil erosion.

Compost production is a complex process, particularly at a large commercial scale, in which a lot of regulations are involved at the local level, according to the same report in Miami Herald. With the passing of a legislative item regarding composting in our County, which was sponsored by Commissioner Eileen Higgins, more commercial compost production may be expected in the future in our area.

Characteristics of final compost could be affected by parent materials (food waste, plant materials, biosolids) used, types of processing, and maturity of the compost, according to a publication by Dr. Moore, a professor at the University of Florida. The final compost needs to meet certain criteria to be suitable for use as a component of the growing substrate for plants, particularly for those grown in containers. Furthermore, the correct application of compost is also important to make full use of this beneficial and environment-friendly product. When applying compost to a tree, like a palm, the correct way is to leave the compost some distance from the stem or trunk of the tree, rather than the way seen in this picture, which may lead to rot of the trunk. This may not be a rare phenomenon for regular citizens, something I saw during a volunteer event organized by our County Park offices. The volunteers had mulched the trees the same way as shown in the picture. Fortunately, my colleague Barbara found out and helped correct the issue. Additionally, it may not be a good idea to grow plants in pure compost or in soil with too much compost, as this may lead to a deficiency of certain nutrients. Growers of high-value ornamental plants need to be aware that plants may respond differently to the ratio and type of compost used in their substrate, which can be reflected by the pH and electric conduction values of the final growth media. If problematic compost, like unmatured, is used in the substrate, it can damage the tree growth (featured picture) and lead to huge losses to the growers.

Compost production can help reduce the amount of waste in landfills, provide ingredients useful for growing plants, and conserve our natural resources. Knowledge of the correct use of compost will maintain the confidence of the public in this beneficial product and its continuous consumption in our society. More research and extension on the usage of compost will contribute to more knowledge on this important resource and the sustainability of our local economy and ecology.

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