Can Tomato Sauce Be Composted (Composter’s Guide)

Composting is wonderful because it reduces waste and creates rich, nourishing plant food. So many things can be composted, including fruit, vegetables, cardboard, expired herbs and spices, crushed eggshells, cooked pasta, oats, coffee grounds, etc. But what about tomato sauce? Can it be added to your compost pile?

Tomato sauce can be composted, but large quantities can be bad for your compost due to its slight acidity. However, if you have one or two expired bottles of tomato sauce, you can add them to your compost pile as it adds moisture, which is vital for the composting process.

If you are hesitant to compost your expired tomato sauce or pasta sauce, you’ve come to the right place. This article will discuss whether tomato sauce can be composted and how to compost tomato sauce properly.

Key Takeaways

  • Safe to Compost: Tomato sauce can be composted, adding moisture and aiding in pH balance.
  • Quantity Matters: Use in moderation; large amounts can negatively affect compost due to acidity.
  • Avoid Meat Additives: Ensure the sauce is pure and free from meat products.
  • Mixing Ratio: Add a cup of tomato sauce for every 4-6 inches of yard waste.
  • Balance is Key: Maintain a healthy mix of carbon-rich materials in your compost.
  • Aeration and Odor Control: Proper aeration is essential to prevent foul odors and enhance decomposition.

The Science of Composting Tomato Sauce

Food and other organic waste have unique properties that contribute to compost quality. Expired or leftover tomato sauces can safely go into your compost pile as long as they’re pure and don’t contain meat additives.

Here are some qualities of tomato sauces that make them suitable for composting:

High Acidity: Balancing Alkalinity and Nutrient Binding

Tomato fruits have a pH of around 4.5 and a tomato sauce may have a slightly higher pH (5.0) due to added sugars. Tomato paste, on the other hand, has a pH range of 3.5 to 4.7.

Tomato products can sometimes harm your compost pile because their high acidity can kill the good bacteria, which are necessary to break down the organic material. However, they’re beneficial if your compost pile has a lot of alkaline components, such as wood ash and animal manure.

In addition, after about 5 to 10 days, a regular compost pile’s pH level rises to 7.0, releasing an unbearably strong ammonium smell. This is called the thermophilic stage, where the pile generates heat from intense microbial activity. The process releases foul-smelling ammonia gas.

This is where tomato sauce comes in handy. Since tomatoes are acidic, adding an appropriate amount of sauce to the pile will help reduce the pH below 7.0, slow down microbial activity, and control ammonia gas emissions. 

Excessive ammonia gas emissions don’t only release foul odors. They also lead to nutrient loss through the release of nitrogen into the atmosphere, leaving your finished compost with little nitrogen for future garden use.

Moisture Enhancement

The moisture in the tomato sauce (around 70%) is beneficial for a compost pile. A healthy compost pile should contain 40-60% moisture. If there isn’t enough moisture present, the compost will either fail to work or take a very long time for the process to complete.

If you add tomato sauce, ensure that you have enough bulking agents, such as yard waste or sawdust, to add structure to the mix and absorb the excess moisture. Adding a cup of tomato sauce for every 4-6 inches (10-15 cm) of yard waste should be safe.

Food waste produces a bad odor (mainly ammonia and leachate). Therefore, it is important to keep your compost pile well aerated to prevent foul smells and to remain aerobic and free of standing water. You can reduce leachate through sufficient high-carbon bulking agents and aeration. 

Although it is not uncommon to have leachate and odor production, there are ways to make it less unpleasant. You can also collect the leachate and reapply it to the compost.

Layering, Moisture, and Materials

Tomato sauce has a low C/N at approximately 5-6:1. You must consider this to ensure healthy composting. A pile’s total carbon-to-nitrogen (C/N) ratio should be about 25-30:1.

With these in mind, you must be careful when layering your compost pile using tomato sauce. The perfect ratio for a compost pile is 1 part nitrogen-rich or green material for every 2-3 parts carbon-rich or brown material.

Carbon-rich or brown materials can include:

  • Straw
  • Hay
  • Untreated sawdust
  • Cornstalks
  • Sod
  • Chopped corncobs
  • Small twigs
  • Wood chips
  • Dried leaves

Nitrogen-rich or green materials can include:

  • Vegetable & fruit waste
  • Grass clippings
  • Manure 

Materials to Avoid

Start to layer everything you want to compost in the designated composting area, but avoid adding ingredients like:

  • Diseased plants that can transfer bacterial or fungal issues to your compost, which could contaminate your garden
  • Meat, which produces a bad odor and attracts rodents
  • Milk & milk products that tend to produce a bad odor and attract rodents
  • Cooking oils, which upsets the moisture balance of the compost pile and attract animals and insects
  • Bread products that can attract pests
  • Rice, which, when raw, can attract insects and rodents, and when cooked, it can breed dangerous bacteria.
  • Colored & glossy paper, as the foils from the ink do not break down and will cause your compost to contain chemicals.
  • Human & pet waste that produces a bad odor and can create a health risk
  • Walnuts contain juglone, which is toxic to some plants.

Proper Layering

You should layer greens and browns in your composting unit like lasagna to ensure that the food is completely covered as it breaks down.

  1. Add 4-6 inches (10-15 cm) of the brown materials, followed by a slight mist of water and a cup of tomato sauce.
  2. Add 2 inches (5 cm) of green materials, another slight water mist, and another cup of tomato sauce.
  3. Repeat the layers until there are no materials left.
  4. Add a 1-2-inch (2.5-5 cm) layer of topsoil followed by another light misting to keep pests off the pile. Only use sterile potting soil or garden soil free of insecticides, fungicides, or bactericides.

Maintaining Your Compost Pile

Looking after your compost pile is relatively straightforward. The important thing is to turn the pile once a week or when the pile’s temperature falls below 110 °F (43 °C) to ensure that the new or outer materials get a chance to be in the center of the pile where the most heat is. 

This is where the organic materials break down the fastest. When you have more materials you want to add to the pile, add them in layers with the mist and tomato sauce in between, like you did when you started the pile. Turn the new materials into the pile immediately using a garden fork. 

If you have added many carbon materials, give the pile a misting using the fine setting of your garden hose to keep the moisture level at the correct percentage. You’ll know that the pile is moist enough when you get a handful and see that it has the texture of a squeezed sponge.

Considerations for Composting Tomato Plants

Since it is possible to compost tomato sauce, it begs the question of whether you can compost the tomato plant as well. Some gardeners are all for composting tomato plants and have done so with satisfying results, whereas others are more reluctant to add them to their compost piles. 

There are a few things to consider before you add the last of the season’s tomato plants onto a compost pile, including:

Avoid Diseased Plants

Avoid adding sick tomato fruits or plants to your compost pile. Diseases like bacterial canker and Fusarium are resilient pathogens often transferred by tomato plants. These diseases can survive the composting process and will likely affect the garden plants that receive the finished compost.

Dice or Chop the Tomatoes Into Small Pieces

Placing large tomato plants to compost could become problematic should the pile not be managed properly. You could end up with unsightly compost containing large pieces of tomato plants that did not decompose successfully.

Remove All the Seeds

It’s crucial to remove the tomato seeds before adding the fruits to the pile. Composting may not necessarily kill all the tomato seeds that remain in the plant and could result in tomato plants growing in your garden where you don’t want them.

Final Thoughts

Composting tomato sauce can be beneficial for a compost pile with alkaline components. The sauce can lower the pH and prevent excessive release of ammonia gas. It also contributes to the moisture requirement of the pile.

However, the compost pile requires careful balance and monitoring. The key here is moderation and monitoring the pH, moisture, and temperature to keep the compost from going bad.

Dr. Moritz Picot

Dr. Moritz Picot is a horticulture enthusiast and the founder of TheGrowingLeaf.com, where he serves as the lead content writer. He established the website in 2022 as a valuable resource for both gardening aficionados and beginners, compiling all the gardening tips he has accumulated over the past 25 years. Alex has a passion for nurturing plants, transforming backyards into inviting spaces, and sharing his knowledge with the world.

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