Compost Accelerators, Starters and Activators

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Robert Pavlis

Compost accelerators, compost starters and compost activators are all terms used for products that are added to the compost pile to make better compost and to make composting faster. What is the difference between these terms? Are they required for composting, and how much faster is the composting process if you use them?

compost accelerators, compost starts, compost activators, compost boosters
Compost Accelerators, Starters and Activators

Compost Accelerators, Starters and Activators

Let’s first try to understand the different terms. I spent some time looking for definitions of these terms and looked at a lot of products that use the terms. My conclusion is that the terms are used interchangeably, or they are used incorrectly a lot of the time. I could not find clear definitions for any of the terms.

However, products being sold under these terms do not all contain the same ingredients. Bottom line, I think it is best to ignore the terms, and look at the ingredients in the box which is what I will do in this article. I’ll discuss the ingredients instead of looking at accelerators, starters and activators.

How do you find out what the ingredients are in a certain product? Simple, right – look at the label. Wrong. Almost none of these products list their ingredients. They might say something like “contains bacteria” but they never say which ones or how much. They might also mention fertilizer – but they never give details. This lack of information should be a big red warning sign – DO NOT BUY!

Microbe Science for Gardeners Book, by Robert Pavlis

Microbial Inoculant and Soil Inoculant

Microbial inoculants and soil inoculants contain microbes. We all know that microbes are responsible for the composting process and so it seems to make sense that we should add some at the start of the process to speed it up.

All of the organic matter you add to the compost pile is covered with huge amounts of bacteria and fungi spores. You can’t see them, but they are there. It makes no sense to go out and buy some more to add to the pile. Don’t believe claims that microbe inoculants will speed up the process.

The other thing to understand about composting is that it is a very dynamic process—I discussed this in Compost Microbes – Good For The Soil. As the compost pile warms up, the microbe populations change. As water levels change, so do the microbe populations. If the environmental conditions are favorable for a certain microbe, it will find the compost pile and it will prosper. They are everywhere. And if you add microbes that don’t like the current conditions they will die. Purchased microbes may already be dead when you buy them, or they might die as soon as you add them – you have no way of knowing.

Lime and pH Balancers

Many composting recipes advise you to add lime, which will raise the pH of the compost. Some products claim that they include ‘pH balancers’ and or lime.

How important is it to keep a correct pH?

To better understand this, lets look at the changes in pH as the composting process proceeds.

The initial pH of garbage, yard clippings and manure will have a pH of between 5 and 7. Manure tends to be at the upper end of this rage, close to 7, and woody products (woody stems, paper) tend to be more acidic. So the starting pH depends on what goes into the pile. All of these things will compost, so starting pH does not seem to be that important.

In the first few days of composting, acids are produced and these will lower the pH to about 5. Some scientists have suggested that this early acidic phase may be very important for killing pathogens, so adding lime may actually prevent the killing of pathogens.

As composting proceeds, the pH will slowly increase to a final pH of about 7 to 7.5.

The composting process manages its own pH and it does not need our help to adjust the pH during the process. The microbes will adjust their populations to match the pH for us.

Secondly, since most finished compost is neutral or slightly alkaline, it makes no sense to add lime to the process—it will only make your finished compost more alkaline. Most plants prefer a pH below 7. Excess lime will also release more ammonia, and you want to keep as much of the nitrogen in the compost as you can.

Bottom line—don’t worry about the pH, don’t add pH balancers, and don’t add lime.


The only reason to add fertilizer to a compost pile is to help feed the microbes. They certainly don’t need more phosphorus and potassium, but if your compost pile ingredients are mostly browns (see How to Compost – Browns & Greens), there will be a deficiency of nitrogen. Adding more nitrogen will speed up composting.

Good nitrogen sources include Urea, blood meal, grass clippings and alfalfa meal. These are much better for the compost pile than compost accelerators, compost starters and compost activators – and cheaper!

Energy Source

Some products claim to contain an ‘energy source’. I guess they think you need this extra energy to wake up the microbes so they will do their job. What these manufacturers fail to realize is that almost everything in the compost pile is an ‘energy source’ for microbes.

Some people talk about adding sugar, molasses, or milk for the same reason. Adding food that has spoiled can certainly be composted—there is no problem adding these items. But they are not needed to make compost nor do they speed up the composting process to any great degree. And I think that adding good food to a compost pile is environmentally irresponsible – donate it to someone who does not have enough to eat.


A number of web sites recommend adding worms to a compost pile—they are wrong. There is a composting process call vermicomposting, or worm composting, that uses worms, but that is a completely different process than using a compost pile. A compost pile gets hot and will fry the worms. Actually, the worms are smart enough to leave as the pile gets too hot.

You might see worms in the finished compost, but that is because they have moved into the pile near the end of the composting process.

Handful of Soil

Earlier in this post I said that you do not need to add a commercial source of microbes, because they are already on the ingredients. If you think that your plant refuge might be too clean—its not—then feel free to add some soil into the compost pile. The soil will add more microbes and costs you nothing.

The soil is not needed, but will not harm the composting process. If it makes you feel good, add a handful or two of soil.

Compost Accelerators, Starters and Activators

I am amazed at how many such products exist—hundreds of different brands. I am even more amazed that many provide no information about their ingredients. Nor do they provide any kind of test results to show that their products actually work. But people must be buying them!

The reality is that composting happens in nature once microbes and organic matter meet. A compost pile provides the mass to produce good heat to speed up the process along, but composting happens even without a pile.

In a future post I’ll look at ways to speed up the process.

Adding compost accelerators, compost starters, compost activators, compost boosters etc, is a waste of money and resources.


1) Photo Source: SKS Bottle & Packaging Inc

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

48 thoughts on “Compost Accelerators, Starters and Activators”

  1. Hi, Thank you for your article; very informative. I have a Vitamix Foodilizer, which greatly reduces scrap volume by 50 to 75% of original volume. What it really does is dehydrate by heating at high temp and grinding the food scraps. What do you suggest to add to “reactivate” it or add microbes destroyed by the heating? Do I need to add any browns to it or worm castings? They sell Foodilizer tablets, but not sure what that does. Thank you!


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