When is my compost ready to use?

This was a question that two new owners of a Green Johanna were asking themselves in their first year of composting. 

Adam and Hayley decided to try composting with a Johanna last year following a few failed attempts with other composters.

They’re both vegans and wanted to produce their own compost to use for growing their own veg, as well as recycling their food and garden waste sustainably.   

  The standard test for when compost is ready for use is that it is dark brown in colour, crumbly in texture and has a pleasant, earthy smell like damp woodland. If you’ve been hot composting, the mature compost will no longer be generating heat. The original materials should not be recognisable. There may be a few items that have not fully broken down, such as sticks, bits of tea bags, corncobs, eggshells, fruit stones, compostable bags – these can be picked out and added back into the next batch of composting material.

 If there are other recognisable waste items and an unpleasant smell, the compost is not ready and should be left to continue breaking down.

Master composter Rod Weston, in his book A Gardener’s Guide to Composting Techniques, suggests a test to check if compost is ready if you are wanting to add it to soil immediately (immature compost added to soil can cause a temporary reduction in the availability of nitrogen and oxygen and create root-inhibiting organic acids).

The test involves putting a handful of compost in a plastic bag and sealing it for three days at room temperature. If when opened the contents have a pleasant earthy smell, composting is complete.

 Rod suggests that during the growing season immature compost is best used as surface mulch. If mostly composted it will finish breaking down in the soil. In autumn and winter it can be dug into garden beds. Some people prefer to leave their compost breaking down over winter to have it ready for the start of a new growing season. 

Horticulturalist and author Charles Dowding encourages a relaxed approach to the final product. In his No-Dig Children’s Gardening Book (also a good read for adults) he says that mature compost can be anything from ‘slightly lumpy and fibrous to quite fine and soft’. It all depends on the materials that went into making it and they will all decompose at different rates.

‘It doesn’t need to look perfect – woody bits in your compost make great food for fungi.’

He cautions against sieving compost as it can damage microbes.

What’s the difference between compost and humus?

The term compost describes materials that are still breaking down whereas humus is what’s left when breakdown is no longer taking place and the usable chemicals in the organic matter have been extracted by the micro-organisms.

It takes years for compost to decompose into a humus state. Even mature compost isn’t really ‘finished’ since bugs and fungi still have material to work on. Some gardeners have a bank of composters and leave the final one to break down completely into humus.  

A bumper crop

Adam and Hayley decided to leave their compost for about a year so they could use it in a compost mix for growing potatoes.

With first-time use of a Green Johanna, it can take 6-8 months for compost to be ready for use. After that, depending on conditions, it’s usually 4-6 months. With regular cold composting it’s usually between 6 months to 2 years.

Great compost accelerator

The couple also used a bokashi bin alongside their Johanna.  The pre-compost that a bokashi bin produces makes an excellent compost accelerator, raising temperature and speeding up decomposition. Fermented bokashi mixture is usually quite wet so needs to be balanced with plenty of carbon-rich materials. The bokashi mixture will then break down in the composter. 

 ‘Bokashi has become a really useful part of our composting process,’ said Adam. ‘We put all our food waste straight into the bin and give it a few sprays of Bokashi spray, then once it’s full and has been left to ferment we transfer it to the Johanna.’

It usually takes them around one to two weeks to fill the Bokashi bin with their kitchen waste, which is usually vegetable scraps along with some beans. They then use their smaller kitchen caddy to take food waste to the Johanna while the Bokashi bin is ‘doing its thing’.

Food waste provides the compost mix with nitrogen-rich content, which must be balanced with shredded carbon-rich materials (dead leaves, twigs, branches, wood chips, paper waste) and regularly aerated to get oxygen into the pile.

The verdict on the Johanna:

With previous composting attempts, the couple had experienced slow breakdown of waste materials with hardly any compost produced.  

 ‘The Johanna is much better built and works faster at breaking down all the waste,’ said Adam.

The couple feel their efforts with the Johanna and Bokashi have paid off – not only are they recycling all their food and garden waste nature’s way, but they also get to make their own delicious home-grown spuds. What’s not to like? 

Spare Parts