Compost disappears over time as the organic matter is broken down by bacteria, fungi, insects and worms. The volume of the compost will decrease but the nutrients will be concentrated ready to add to your soil. Compost piles can decrease in size by half as the ingredients are broken down, air pockets decrease in size and larger pieces are decomposed.
Compost that is broken down and concentrated over time is actually a good thing. This means that the larger pieces are being broken down so they can be mixed into your garden soil. The bacteria and worms will mix and break down larger pieces releasing nutrients into the compost so your plants can absorb them.
Over time the deepest layers of compost can even break down or anaerobically ferment turning into humus, a deep dark soil like material that is rich in nutrients and helps the soil to hold water.
Compost can look like it disappears over time and most of the time this is a good thing. This article will explore the top 5 reasons why compost seems to disappear over time.
5 Reasons why compost disappears
Here are the top 5 reasons why compost disappears over time. Some are the natural process of breakdown, others might need you to add extra water or ingredients.
1. Bacterial and fungal break down
Bacteria and fungi are the main contributors to compost breaking down over time. They exist naturally in soil and organic matter and move in to break down your compost ingredients. Different bacteria and fungi thrive in different environments.
If you are running a cold composting pile then aerobic bacteria or those that break down organic matter using oxygen will thrive. Hot composting piles will be mainly made up of anaerobic bacteria and fungi that do not need oxygen to break down the ingredients.
To help compost break down as fast as possible, turn and mix the pile every 2-3 weeks to add extra oxygen and increase contact between ingredients. Keep the pile moist but not wet and
You want the organic matter to be broken down in your compost pile until the ingredients are no longer individually recognizable. The pile will decrease in size, by up to half but that is a good sign. It means that the organic matter is broken down making the nutrients available for your plants.
2. Worms and insects
Worms and insects that decompose compost material are another big contributor to your compost materials disappearing over time. Cockroaches, beetles, caterpillars, slugs, snails and even grasshoppers can all move in and break down the organic matter in your compost bin.
If your compost materials are in balance then these creatures will work in harmony to break down the surface, upper layers and deeper layers of compost. Keep a balanced ratio of around 1/3 green materials like food scraps, coffee grounds and lawn clippings with 2/3 brown materials like hay, straw, fall leaves and dry garden trimmings.
Garden worms will dig up from the ground soil into a moist compost pile to break down the lower layers of the compost. Beetles, slugs, snails and caterpillars will stay near the surface to eat the organic matter on top.
These creatures will keep each other in balance. If you are getting lots of black flies or small vinegar flies around your compost it could be too acidic so mix through some extra brown materials and add a handful of garden lime.
3. Dry weather
Dry and hot weather can cause compost piles to dry out rapidly which can drop their level and make it seem like the ingredients have disappeared. Compost piles that dry out can compact and drop in level rapidly.
It is important to keep compost piles moist in hot weather to keep the soil bacteria and fungi alive. Worms will disappear deeper into the soil if it gets too dry and will stop digesting the organic material.
Cover compost piles with shadecloth on very hot days and give it a good soak in the morning if you know that the weather will be extreme.
4. Too much water
Compost piles that are too wet can seem to disappear. This is because the ingredients will become compacted and the level will drop. This will reduce the oxygen available in the mix causing it to break down anaerobically.
Too much water mixed with anaerobic break down can cause the ingredients to rot and smell. Compost piles should be moist but not too wet. They usually can find balance just with the green and brown ingredients you add.
If your compost pile has become too wet, add some extra brown materials like hay, straw, fall leaves or shredded, plain paper to absorb some of the moisture.
4. Less air
Compost piles that are neglected or left on their own without adding extra ingredients or tuning will compact over time reducing the air component. Even the natural break down process will reduce the size of the organic matter pieces and cause the pile to start to disappear.
Reducing large air pockets is a good thing and is part of the process of the compost being broken down. When compost is ready to add to soil it will look dark, crumbly and the larger pieces will have been broken down.
It is best to avoid adding compost with large pieces to your soil before they are broken down. They can interfere with plant root growth and cause large air pockets in the soil.
5. Turning into humus
If compost is left for a long time to break down, in perfect conditions the bottom layers can turn into humus. Humus is a dark, rich ingredient which is made by anaerobic fermentation of organic materials. It is difficult to deliberately make but it will occur naturally over time.
This material will be a fraction of the size of the original ingredients as it is very concentrated. It is an amazing ingredient for your garden and helps the soil to hold water for longer.
Why Compost Disappears | Summary
Compost piles or bags can seem to disappear in volume over time. Don’t worry if the compost is still moist because this is a natural process where the organic material is being digested and concentrated. To keep your compost healthy and ready to use for longer, turn it every few weeks and keep it moist. It will keep well until you are ready add it to your garden.
I am an accredited practicing dietitian, experienced gardener and a dedicated cook. I love writing and sharing my experience so you can learn from my successes and mistakes.