Composting is a great way to create organic and nutrient-rich food for your garden but many people think that the process is complex and far too time-consuming. However, more and more gardeners are jumping on the ‘composing in builder’s bags’ wagon and are having some great results. Of course, as with anything, there is a knack for getting it right but it’s simple and almost anyone can do it. In this short guide, we will be looking at how to start composting in a builder’s bag, even if you have no previous experience.

Leaf litter in compost bag
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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.

Why Should I Start Composting?

If you are new to composting, you might be wondering what the point of this process is. The great news is that there are a huge array of benefits to composting so even if you have stumbled upon this guide by chance, allow us the opportunity to tell you why composting is a worthwhile activity. In the main, there are two reasons why composting is worth considering. In a world where being eco-friendly has more significance than ever, composting is an easy and viable way for gardeners to do their bit. Research has shown that in the USA in 2018, only 4.1% of food waste was recycled; that is an astonishingly low figure and is similar in other countries around the globe. By composting your food waste and other organic materials, it is believed that you could reduce your carbon footprint by a seriously impressive amount. In fact, composting for one year will save the equivalent of the number of harmful gases put out by your washing machine in three months.

Furthermore, your plants will thank you. Compost is one of the most natural and effective ways to feed your garden and when applied regularly, you should notice significant changes in the health of your plants. Compost is incredibly rich in nutrients and this has several benefits for your garden including stabilising the soil’s pH balance, improving moisture and benefitting the soil structure.

What Does Compost Need?

If you want to get started on composting then there are a few key ingredients that will see you succeed. Without each of these things, the compost will not fully develop to its best, but using a builder’s bag will provide you with each of these things in just the right measures.

  • Air flow is essential to prevent the compost from smelling.
  • Compost needs heat in order to break down the organic material; some would say this was the engine of the process.
  • Moisture is needed to keep the compost hydrated.
  • Compost doesn’t develop overnight, this is a process that requires time.
  • Vegetation is required to keep the compost thriving.
Compost in Builder's Bag
Compost in Builder’s Bag

How To Compost Using Builders Bags?

When most people think about composting, they imagine using a compost bin or large container. Perhaps you aren’t able to get your hands on one of these or would like to try something a little different. In that case, switching to a builder’s bag could be a great alternative.

These bags, which are used for transporting sand, soil, stones and other materials are the perfect shape and size and provide excellent conditions for your compost to develop. They won’t rot and are incredibly strong, so once you have your established compost bag, there’s a very limited worry about its durability over the long term.

Step One – Source Your Bag

If you are fortunate enough to have a builders bag lying around in the garden after delivery of aggregates for your latest garden project, then you pretty much have everything you need. However, if you’re short of a builder’s bag, they are relatively easy to come by. You might try approaching your local builder and seeing if you can take a bag for a small cost.

Step Two – Finding The Right Location

One of the most important things to think about when starting to compost with a builder’s bag is where you will place your setup. In the main, provided that you place the bag somewhere level, you won’t have too many problems. However, you might also wish to consider the fact that these bags aren’t the most aesthetically pleasing so hiding them in a garden work area or behind a fence can be a more preferable option.

If you are concerned about weeds underneath your builder’s bag then it is a good idea to place down some protective material such as a weed barrier. Regardless of where you place your builder’s bag, be sure to leave enough room to comfortably access it.

Step Three – What To Put Into Your Builders Bag Compost

Many people believe that, in order for compost to perfectly develop, there must be a balance of materials inside but this is not always a correct assumption. While it is good to have a balance of materials, the most important thing is to ensure that you fill the bag. As soon as organic material becomes available, throw it in. When you add materials, be sure to level out the compost and ensure that the materials fill each corner at the base of the bag. For the first few weeks, you will notice that the compost bag fills up very quickly. As materials at the bottom begin to degrade, the level will gradually drop, leaving you more room to add additional materials. You can put any of the following into your bag:

  • Grass clippings
  • Leaves
  • Rotten fruit
  • Vegetables or veg waste
  • Hedge trimmings that do not contain wood
  • Soft weeds

That being said, there are some products that should be avoided, these include bones or meat, wood, thorny plants such as roses, and perennial weeds.

Step Four – Maintaining Your Compost

Once you have everything in place, you will need to maintain your compost. When your bag is filling up, you will need to compact the materials as densely as possible. You can do this by either standing on it and using the bag’s handles to pull the sides up or you may simply use the back of a shovel to flatten the contents.

In any case, you will find that the bag quickly fills up and when no more can be added, you will need to cover it with a thick material such as an old piece of carpet and leave it alone for up to six months. It can be tempting to add more as the compost pile reduces but it is important not to do this. If you want to keep composting, you can start a new bag.

Step Five – Using The Compost

Now that everything has nicely developed, you will be able to use your compost as mulch around your garden. Before adding it to the soil, it is important to give it a stir and check for any non-composted materials. These can be added to a new bag and left for an additional few months.

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.


Composting is an excellent way to add important nutrients to your garden and cut down on waste. While some of the commercially available composting bins can be quite costly, a builder’s bag is a great alternative. Getting started is simple and in as little as six months, you will have an ample supply of compost for which your garden will thank you.

How To Compost Using Builders Bags Infographic

Garden Doctor Tips

“Remember that your compost will need a little moisture but do not over-soak!”

“Add anything organic and uncooked – veg peelings are a must and must not be thrown away!”

“Do not add perennial weeds to your compost, they may take root and start to grow again!”

“The beauty of composting is that it can be done anywhere and almost anything can be used to make it!”

Frequently Asked Questions

What is the process of composting?

Composting is a process that turns organic material into nutrient-rich soil. It can be done in the backyard, on a farm, or in an industrial facility. When composting, you take waste such as fruit and vegetable scraps and combine it with other materials like dead leaves and straw to create black gold-rich soil that helps plants grow!

What can you put in your compost bin?

What can you put in your compost bin? Well, there are quite a few things that can go into your compost bin. Think about all the fruits and vegetables that you throw away when they start to rot – those items are perfect for your compost bin! There is also grass clippings, leaves, eggshells… The list goes on and on. And what can’t you put in it? That’s an easy question – anything with meat or dairy products cannot be added to the compost pile.

What is bad about composting?

Composting is a great way to reuse organic material. But, there are some drawbacks that may not be so obvious. For example, you need a lot of space to compost properly and it can take several months before the compost is ready for use in your garden or flower beds.

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.

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.

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.

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’.

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.

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. 

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 will start declining.

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.

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.

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).

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.

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.

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 🙂

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.

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.

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.

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


Trevor Wright is not just a seasoned horticulturist; he’s the esteemed Garden Doctor. With a BSc in Horticulture and years of hands-on experience in the soil, Trevor has become a trusted mentor for all things gardening. As the founder of Garden Doctor, he’s committed to clarifying the intricacies of gardening, offering straightforward advice that’s rooted in years of practice. His writing is a garden of how-tos, savvy insights, and comprehensive guides that enable individuals to nurture and grow their garden dreams. When he’s not knee-deep in garden beds, Trevor is at his keyboard passing on his green-thumbed wisdom to budding gardeners, ensuring that the legacy of sustainable and joyful gardening blossoms far and wide.

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