A popular composting question we get asked is whether eggshells will compost in the HOTBIN. Although it may seem like a myth, like most things, eggshells do break down over time and this article covers the science behind why we say they can be added into the HOTBIN.
What Does an Eggshell Consist of?
An eggshell is a natural source of calcium with the shell made almost entirely from calcium carbonate - it’s one of nature’s great designs really!
Calcium carbonate can be likened to lime/chalk, which although difficult to digest by bacteria in a cold compost heap, is susceptible to heat. This exposure to heat causes the shell to soften and weather resulting in it becoming brittle.
Benefits of Adding Calcium to Soil
The process of liming is well known to seasoned gardeners. This is where lime is added to acidic soil to increase calcium content, to raise the soil pH, and improve soil quality.
Similarly, to a human diet where calcium is needed for strong bones, calcium is essential for supporting cell growth in plants to ensure strong plant walls and healthy growth.
How to Compost Eggshells in the HOTBIN
If adding eggshells into the HOTBIN it is recommended that they are crushed into fragments before adding. When processed inside at temperatures of 40-60°c the heat inside the HOTBIN causes the shell fragments to become brittle encouraging them to breakdown much faster than they would have done if the shells had bypassed the hot composting process.
When harvesting a batch of HOTBIN compost you may well still see small bits of shell, these however will be quite brittle which means when added to flower beds they will break down/crumble quickly releasing calcium into the soil faster too.
Different Uses for Eggshells
If you do not wish to compost eggshells, then there are several other uses for them:- Eggshells provide further benefits such as enhanced aeration when added directly into the soil.
- It is claimed that eggshells act as a slug deterrent because of the sharp surface they create for the pests.
- If you fancy being creative, half shells can be used as starter pots for seedlings providing them with calcium benefits from the very start.