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When should I harvest? A guide to harvesting your compost bin

There are many different methods of composting available to gardeners, but whichever method we choose, the end result we are after is something that turns our household organic materials into a rich soil amendment that will add nutrients and help improve the structure of our soil to help our plants thrive. The double bonus is that by doing this at home we are keeping those organic materials out of landfill where they break down into climate damaging substances such as methane.

Whatever method of composting you wish to use; it is really important to make sure that the compost is fully mature before you dig it into your soil. Let’s look closer at the idea of compost maturity. Composting is all about taking something that was once living and exposing it to the various compost creatures and microbes that chop the organic material into smaller and smaller molecules. The microbes and other organisms use the nutrients within the compost, such as nitrogen, to build their own cells in order to enable them to break down the tougher and more resistant ‘brown’ (high carbon) materials that are essential to a well-balanced composting process. The ‘green’ components of your compost such as fresh lawn clippings and fruit and vegetable scraps provide the nutrients needed to fully decompose all the woody brown materials.

There are obviously various stages of decomposition along the composting journey, but at the final stage of composting we are left with a rich dark substance called humus. Compost heaps will not reach maturity if there are issues such as an incorrect nutrient balance, too much or too little moisture, or a lack of aeration. Such problems can be fairly easily corrected in most cases to resurrect a stalled compost heap and help it reach maturity and we will cover that later in this blog.

The key to knowing when to harvest from your compost bin lies in identifying when most of the contents have reached the final breakdown stage and have become humus, signifying that your compost is mature and ready to go on the garden.

Tell-tale signs to look for in compost that is ready include:

  • It should be dark and crumbly and not stick together as a sodden, lumpy mass
  • It should not have any unpleasant or strong odours as this could indicate that it has not had sufficient oxygen present to produce humus
  • The compost mass should be roughly at room temperature and not be at all hot or give of steam
  • A very simple test you can do on compost before use is to germinate some quick growing seeds such as radishes, kale or lettuce in a pot of the what you hope is mature compost ready to use in the garden. If the seeds do not germinate or grow poorly or are off colour then you will know there is a problem and that it should not be used in its ‘immature’ state.


How to make harvesting compost super easy
One of the most practical composting options of all is a cold compost bin that has a flap or opening at the base which allows you to remove mature compost that has gradually worked its way to the bottom of the heap over several months. Regular removal of finished compost causes the heap to drop in the bin thus making room for fresh material to be added at the top. This is a very practical option for gardeners who generate small amounts of organic waste (such as kitchen scraps) on a daily basis.
Another tip for harvesting compost from an established pile is the Tumbleweed Compost Mate or ‘compost corkscrew’, which is without doubt one of the best composting tools ever invented as it takes all the back breaking work out of aerating and turning your compost heap to help accelerate the process. As well as using it that way, you can also use it to easily extract mature compost from the middle or base of an established compost bin or heap. By winding the Compost Mate down into the heap, you are filling its core up with compost that can be lifted out of the heap and into a bucket for distribution to the garden

How to speed up a stalled compost to ensure it reaches maturity
One of the most critical elements in any composting system is having the right balance of nutrients to fuel the growth of the microbes responsible for organic matter decomposition. A good practical way to ensure you create the right balance is to always place a thin layer of high nutrient material such as manure or kitchen scraps directly on top of each layer of low nutrient material such as straw, dead leaves, bark or shredded paper. If you feel your compost has stalled you can simply add extra nutrients in the form of a liquid manure made by soaking some animal manure in water. Or you can add the concentrated liquid that can be collected from an above ground worm farm that is not only full of nutrients, but also a healthy dose of compost microbes to get your heap back on track.
Aeration can be achieved most simply by turning the heap with a pitchfork but if space is limited specialised tools such as the Tumbleweed Compost Mate that can be used to turn the heap in situ. Alternatively drill lots of holes in some rigid plastic pipes and insert them into your heap whether it is a cold or hot heap and leave it in place to give constant aeration. Tumbleweed compost tumblers are another practical solution to the issue of oxygenating compost in a small space. Giving the compost a turn every few days will significantly increase the speed of decomposition.
The microbes that break down organic matter respire in the same way animals and plants do and therefore need a certain level of moisture as well as oxygen to function. If the heap is too dry activity slows down. On the other hand, if there is too much moisture there is not enough room in the pore spaces of the heap for the oxygen they require. A great rule of thumb is that you should be able to squeeze only a few drops of moisture from a handful of the material from the heap. It is OK to simply hose the heap down if it is too dry.
Another tip to helping achieve mature compost quicker is that by finely chopping up organic materials you can greatly increase the surface area available to the micro-organisms that decompose your compost to speed up the process and help ensure success. For kitchen scraps like orange skins and egg shells simply take a little extra time to dice or crush them up before adding to the compost. For bulkier materials such as garden pruning’s, put them on the lawn and run over them with the mower and catch the resulting finely chopped residue which will break down far more quickly as a result.
Using compost in the garden
Using the tips in this blog you are now ready to harvest your compost and put it to work. All compost is fantastic as a soil conditioner that will boost your soil’s capacity to store both water and nutrients. Mature compost, whether it be from a worm farm or compost bin, is best dug into the soil before planting. Alternatively, if you want to feed plants that are already established a great strategy is to put down a layer about 5 cm thick around the base of the plant. Then put a mulch layer on top of the compost, such as lucerne hay or pea straw. The native earthworms that live in your garden will come up and feed on the compost below the mulch and take it down into the root zone of your plants. The worm population in your soil will increase and as they do, they will aerate and cultivate the soil around the root zone, and your garden will love you for it!

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