Composting is the natural process of recycling organic matter into a nutrient-rich soil amendment called humus. Tomato scraps, including fruit, vines, and leaves, are excellent additions. The fresh material is considered a “green,” or nitrogen-rich, component that fuels microbial activity within the compost pile. However, successful composting requires managing two primary concerns: the survival of seeds and the potential spread of plant disease.
General Suitability of Tomato Scraps
Tomato waste is highly suitable for composting because of its composition. The fleshy fruit and soft tissues possess a high moisture content, which is necessary for microbial breakdown. This moisture and soft structure allow tomatoes to decompose rapidly compared to dry, woody materials.
As a “green” material, fresh tomato scraps provide a significant source of nitrogen to the composting microorganisms. Nitrogen is the building block for the proteins and enzymes these organisms need to multiply and break down carbon-rich “brown” materials. This accelerates the overall decomposition rate of the entire pile.
Preventing Volunteer Tomato Plants
The seeds encased within tomato fruit are remarkably resilient and can easily survive the typical cold composting process. These tough seeds often remain viable, leading to unwanted tomato seedlings, known as “volunteer plants,” sprouting when the finished compost is spread in the garden.
The most effective strategy to ensure seed death is to employ a hot composting method. This requires maintaining the internal temperature of the pile at or above 131°F (55°C) for at least three consecutive days. This sustained heat is sufficient to denature the proteins within the seeds, rendering them non-viable.
If maintaining such high temperatures is not feasible, an alternative method is to bury the tomato waste deep within the center of a large, active pile. Microorganisms are most abundant and decomposition is highest in the core, which may destroy some seeds. Another approach is to ferment the fruit waste separately in a sealed container for a few weeks before adding it to the pile, which can also help break down the seed structure.
Guidelines for Diseased Tomato Material
Composting diseased tomato plants presents a significant risk of reintroducing pathogens into your garden soil. Tomatoes are susceptible to fungal diseases like late blight and bacterial infections such as fusarium wilt. The spores or resting structures of these pathogens can survive on infected plant tissue, even after the tissue has dried out.
A strict guideline for home composters is to never add any plant material showing signs of disease, such as leaf spots, wilting, or rot. Most backyard compost piles cannot reliably kill all destructive pathogens. Diseases like fusarium wilt are challenging because their structures can persist in the soil for years.
The only safe way to compost diseased material is within a professionally managed or industrial composting system, where temperatures consistently reach 140°F (60°C) to 160°F (71°C). For the home gardener, infected leaves, stems, or fruit should be bagged and sent to a landfill or incinerated, to prevent the disease cycle from continuing.
Preparing Tomato Waste for the Pile
Physical preparation of tomato waste is necessary to speed up decomposition and manage its high moisture content. Whole tomatoes, large vines, or thick stems take a long time to break down. Chopping all material into pieces no larger than one or two inches increases the surface area available to the composting microbes.
Because tomatoes are mostly water, adding a large volume can quickly make a compost pile soggy, leading to anaerobic conditions and unpleasant odors. To prevent this, the nitrogen-rich tomato scraps must be balanced with sufficient carbon-rich “brown” materials. Balancing agents include dry leaves, shredded newspaper, wood shavings, or straw.
A general ratio of about three parts brown material to one part green material by volume helps to absorb the excess moisture and maintain proper air circulation. Layering the chopped tomatoes between these dry, carbon sources ensures the pile remains porous and oxygenated for efficient and odor-free composting.