Compost Pile

Compost is a wonderful tool in the garden, but how do you know if it is what your plants need? We have compiled a list of frequently asked questions about compost, and we are answering them here.

From the benefits of compost to whether or not it can be used as mulch, this article covers all the bases so that you can make informed decisions when making compost for your garden. 

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1. What is Compost?

Compost is the result of composting. Composting is the process of breaking down organic materials to create a nice, nutrient-rich, earthy substance that can be used as an organic soil amendment in the garden.

Compost is perfect for use in growing vegetables or flowers – ready to enliven your backyard garden!

The most common ingredients are leaves, brown twigs and sticks, grass clippings from lawns, sawdust, and crop residues like corn stalks and straw. It is important to remember that these should be chipped or shredded into small pieces at least one inch in length before adding more debris.

Covering this mix with mulched leaves or other compostable material helps regulate the temperature necessary for decomposition while keeping out animals such as foxes and rats looking for a free meal.

2. Is Compost the Same as Soil?

No, compost is not the same as soil. Compost is the nutrient-dense natural result of the decomposition process of organic materials such as kitchen scraps and garden waste.

Soil is made up of composed mineral grains that have been formed by weathering and erosion over millions of years, along with organics rolling in from fallen foliage.

Compost is used to enrich the quality of soil and even though they are both “earthy,” they serve different purposes and cannot be used interchangeably.

3. How Do You Know When Compost is Ready?

A compost pile will typically exhibit the following traits to indicate that it is ready for use in a variety of home gardening applications.

The pile should emit an earthy fragrance, with some fresh, foul odours depending on the exact ratio of green matter and brown matter in the pile.

A good rule of thumb is that if it smells like grass clippings or dog poop, it is not ready! 

The top 6-8 inches of a typical heap should be moist but considerable water cannot be merely squeezed out from below. The material will feel crumbly when you squeeze and release small handfuls between your fingers. It is important not to confuse this ‘crumbliness’ with dryness as complete carbonization is the point of no return.

Much like a cake, you should be able to pull out piece after piece with very little effort. The pile will crumble when pulled apart and not fall back together readily under its own weight (known as ‘cakey’). Being cakey is an indication that there are too many wet materials in the mix or insufficient brown material for carbonization has occurred.

Depending on the conditions, the whole composting process typically takes 3-12 months for all of the materials to break down.

4. How Much Compost Do I Need?

How much compost you need will depend on a variety of things such as what you are growing and the underlying soil type. For example, clay soils will need a little more compost than loamy soils.

In general terms, it is often considered a ‘rule of thumb’ to add one to three inches of compost into the top 6 inches of your soil each growing season.

This, however, is not necessarily true depending on the variables we mentioned above.

5. Can You Reuse Compost?

The short answer is yes, you can reuse compost.

But if you want your garden to flourish (both this year and the next) I recommend using fresh compost each time. To explain why, it helps to know a little about how plants work.

Plants are working 24 hours a day to convert sunlight into energy through photosynthesis. They need all the nutrients they can get their hands on, and they are often things like nitrogen, phosphorus, and potassium. 

Fresh compost provides many of these nutrients needed by plants because it has been created with green materials like grass clippings and vegetable waste that have been broken down organically over time by microorganisms and bacteria.

Be aware that if you do reuse compost, the nutrient content will be diminished, and this is known as being ‘spent’.

6. How to Regenerate Spent Compost?

There are several ways to regenerate spent compost, but in general, if compost is too ‘spent’, it will no longer provide any beneficial nutrients to your plants or soil, so it is important to freshen up and amend the compost.

One way to accomplish this is through transferring finished “compost” from the head end of the container (where fresh materials are being added) – through a device called an upgrader – that mixes it with recently saturated aged material from the tail end of the container so that all compost gets cyclically mixed.

There are also other commercially available products and fertilisers that can be added which will increase the nutrient content of your compost.

7. What to do with Used Tomato Compost?

Ways to use tomato compost around the home include using it as a natural fertilizer or growth medium for plants (for example, in garden pots or window boxes), in your houseplants’ soil, and on your lawn.

Because of its high nitrogen content (more than 6% organic nitrogen), this type of compost should not be used directly from its compost pile for strawberry beds and other plants susceptible to excessive nitrogen levels; instead, it needs to be aged first before applying. 

Tomato compost can also provide nutrients such as calcium, copper, iron, magnesium, and potassium if it is added as an amendment to a soil that has a high clay content. 

8. Can I use Ericaceous Compost for Tomatoes?

While tomato plants may be able to grow quite well in an Ericaceous compost, it may also inhibit their growth. The problem here is of phosphorus availability.

As you may know, phosphates are typically used as a major nutrient source for tomatoes. Well unfortunately this is exactly what the Ericaceous Compost performs so well at breaking down – namely extracting phosphate into the soil and making it unavailable for uptake by the plant roots.

What this means is that over time your tomatoes will stop receiving enough phosphorus and their health starts declining.

9. Is Mushroom Compost Good for Potatoes?

Of course! Mushroom compost is high in calcium, phosphorus, and other micronutrients.

Potatoes grown in properly prepared beds of mushroom compost do not need much fertilizer either which greatly reduces costs associated with nitrogen, potassium, and other fertilizers on top of higher yields overall from potatoes over time.

The only thing that we will say is that using mushroom compost on your potatoes does increase the risk of potato scab, but this is more of a cosmetic problem that does not affect the overall quality and taste of the potato.

Also, if you are only growing earlies, the spuds will not be in the ground long enough to be affected by scab either. Win-Win!

10. Can You Compost Moss?

Composting moss is the subject of much debate as to whether or not you should.

Composting moss is possible, but the process will be terribly slow and inefficient. Moss does not break down like leaves or other organic materials in compost.

The best way to control rotting moss is by adding clay at the bottom of a new pile which will differentiate between decaying and non-decaying biomass; thus, cutting down on decomposition time by fixing potentially foul-smelling waste matter more quickly than an ordinary composter would.

In addition to this, moss should also not exceed 10% of your total compost mixture because it offers little benefit in comparison to other organic materials.

11. Can Shredded Paper be Composted?

Yes, shredded paper can and should be composted. The thing to keep in mind is that the paper should be shredded BEFORE use and that the paper will decompose much faster if there is a lot of heat and moisture present.

Paper shreds are an important addition to any compost heap, as they can provide extra carbon for the balance between nutrient-rich materials that supply nitrogen and plant food (carbon).

Additionally, lack of oxygen inhibits bacterial activity so oxygen from other sources must be provided to maintain adequate conditions for decomposition. 

12. Can You Compost Cardboard?

Yes, you can compost cardboard if it is free from food items or any other contaminating material.

Cardboard is one of the few materials that has many fibres that are plant-based, so cardboard will naturally decompose in your compost pile.

Like shredded paper, cardboard is an important ‘brown’ material that adds value to your composting.

13. Is Coal Ash in Compost Okay?

No. Composting of coal ash would release toxic substances, including heavy metals, sulphate, and lead, into the surrounding environment.

Coal ash is one of the world’s largest sources of industrial waste by volume. It has been linked to environmental contamination and groundwater pollution in communities near coal-fired power plants in the United States.

Long-term exposure to these toxins has been associated with developmental delays, neurological issues, high blood pressure, asthma, and cancer. “Composting” is simply just not ok.

14. Can you Compost Potato Peels?

There are differing opinions on this, some people are against it and others will add them in with no worries.

The only reason for not composting potato peelings is that they are a potential source of the fungus that causes potato blight.

However, there is an easy way to eliminate this concern – bury them well down in your compost and ensure you turn it regularly!

If you are not as active as you should be with your composting, it is probably better you do not add them but if you are on top of it, feel free to add these delicious food scraps into your pile without worrying about any concerns at all 🙂

15. What are the Yellow Balls in Compost?

If we are talking about store-bought compost, those small yellow balls are slow-release fertilisers.

If, however, you have small yellow balls in your homemade compost pile, the chances are that they are some sort of insect eggs. Likely to be worms, slugs, or snails.

16. Can You Compost Flour?

Yes, flour can be composted and is firmly in the ‘brown materials’ camp. In order to help the microbes break down flour, it must first be mixed in with other materials such as leaves, grass clippings or coffee grounds.

If all-natural substances are unavailable, then some non-organic nitrogen sources could be used but these need to oxidize first before they will start providing nutrition for your plants.

It is good practice to add a layer of soil or mulch over any pile you build so that oxygen remains contained within the pile and decomposition occurs more efficiently over a prolonged period of time.

17. How to Tell if Horse Manure is Composted?

Tests exist for other types of compost and their tests work quite well, but there is nothing so far that will tell you if the horse manure is actually a “compost” or just dried dairy cattle manure with some leaves in it.

And until then, all one can do is make an educated guess about what it has become based on its odour, texture, age (sound familiar?), looks (again) as well as the soil around it.

There are certain characteristics one would expect from a natural compost – natural cycles take time to finish reaching an equilibrium of warmth and moisture levels needed by bacteria to break down materials.

For instance, this is why compost piles often have a dark brown or black colour and release an earthy odour.

There are two common characteristics of “compost” that you will also find in traditional fertilizers: carbon (browns) and nitrogen (greens).


I hope we have answered that niggling question that has been bugging you.

Remember, the most important thing about compost is that it should be well-balanced. This means that the right amount of nitrogen, carbon and minerals are all present in order to make your plants thrive.

By following these tips, you can create a healthy balance for your garden as well!

It is not too late to start making this year’s batch of compost so let us know if we can help with any questions or problems along the way – our team would love to hear from you.

Garden Doctor Trev

Garden Doctor Tips

“Make sure you are composting the right materials. You don’t want to add any fats, meat, or dairy!”

“You will need to ensure that your compost is moist and not wet, when squeezed it should feel as damp as a wrung-out sponge!”

“Never add coal ash to your compost pile. It is not good for the environment and will do your plants no good!”

“Only add potato peelings if you are an experienced composter and know what you are doing. For beginners, it is best to wait and learn so you are able to get it right!”

About Me

Hi, I’m Trev and I’ve been growing things since I can remember. When I was younger, I grew up on a farm, so I have always been around plants and animals. After studying horticulture at university, I decided to start my own nursery which I have run now for 25 years. In my spare time, I run this website – which is a resource for people who want to learn more about their gardens.

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