Finiished Compost: The Smell Test

It is easy to test whether the composting process is  finished cjust by using your eyes and nose.    If it looks dark and crumbly, as compost should, smell is an excellent  indicator of healthy compost. Put a good handful into a polythene  bag, and seal it. After 3 or 4 days open the bag and sniff. It has a pleasant earthy smell you are a complete rotter.  

 An unpleasant smell and wet compost use the sponge test to check the moisture content (see the next post) it may have become anaerobic. A smell of ammonia it is likely that it  still has a high nitrogen content and needs more Browns adding.  Compost with a high moisture content  that smells of mildew should be returned to the bin and turned frequently to provide an increased airflow. Would chip could be added to help increase the air spaces, 

The Radish Compost Maturity Germination test

 The length of time it takes to produce mature compost ready to use will vary with the method used and the type of bin  from about a  month to a year product, and the intended use.

However, most composters do not test their compost if it looks and smells OK. Some will go a little further and carry out a smell test. I have always felt that maturity tests where unnecessary on home compost but  there is always a chance that  immature compost  could slip through into use and  kill  or stunt plants. It is also possible that an  herbicide in  the raw products could survive the composting process.  This happened in 2009/10 when  weedkiller damage to plants was traced to farmyard and stable manure used in compost.

A simple Maturity and Germination   test using  radish seeds is quite quick and requires relatively little effort and offers a means of identifying problems before they arise,  the test is successfully passed where 75% of the seeds sow germinate and grow to maturity. Once  harvested a separate  eating test can be undertaken .

 At its simplest the radish seeds can be sprinkled onto the surface of a pot of the compost under test and on a pot of commercial compost being used as a control.   A simple visual  estimate can be  made as to how the two pots compare. In practice, if I just want to check that the compost is suitable for my own use,  I use a 1.2ml ( ¼ tsp) measure and sow the seeds in a  15cm flowerpot of the compost and just estimate whether about  ¾ have germinated.   It is advisable to always use  a control sample of commercially available compost or a previous tested batch of home compost .

A more scientific approach is to sow a known number of seeds. Some methods use  five, eight or ten seeds per pot so that the geminated and mature plants can be counted, and a percentage germination rate calculated. If counting the seeds, I tend to use ten seeds per pot to make the calculation of 75% easier.

 If greater accuracy is required  more pots should be used, some use more pots two or six have been suggested  pots with an equal number of pots for the test and control samples.

 If the germination rate is significantly lower in the test samples than the control the compost is still immature, and the maturation process should be  continued.

The seeds may need to be watered daily to maintain the moisture level.

Radishes are used because they germinate and mature quickly. It should be possible to count the germinated seeds at about seven days and harvest after 4 weeks.

We are currently harvesting compost from our overwintered bins and the photo shows samples from two bins sown and ready to grow with a commercial available compost as a control. Watch this space.



Compost Awareness Week 2021

Maturity Test during Compost Awareness Week


This  Maturity Test could make an interesting competition on an allotment or community composting site where individual members have a dedicated bin. In addition to CAW  on allotments would lend itself to a new “best compost” class at the annual show or as an Allotment Week event.

If you decide to take part either post yout photo on the Carryoncomposting Facebook page and/or send a photo with your details to carryoncomposting1@


Talks in Leicester and Leicestershire and toursof the Stokes woos Composting site can be offered by Rod Weston  please email




International Compost Awareness Week 2-8 May 2021

Started in Canada in 1995, ICAW attracts participation individuals and volunteer groups as well as  businesses, councils  and  schools.

 Throughout the week events are held to encourage and celebrate home, school, community, and industrial composting. The events include tours of compost facilities, school gardening programs, compost workshops, lectures and lots of activity  of t on social media .

CAW UK  The ICAW provides the opportunity for the National Allotment Society (NAS) and Allotment Societies across the country to promote allotment gardening and demonstrate their commitment to reducing waste sent to landfill and good environmental practice. While Master composters,  Garden Organic,  local councils  and others will be organising events over the country during the week,  the NAS, with our network of local allotments, could take the lead in ensuring maximum  community involvement.

Allotment Open Days, School Workshops and Talks

If you site is interested in helping to promote the campaign week  by holding an event, please email with details and we will publicise on this website and social media. Click here for more information.

CLICK HERE to download a pdf of a Compost Presentation from Rod Weston - Master Composter. If you would like the PowerPoint, please email  You need to be aware that the file is 19MB.


The theme for 2021 in the United States is  Grow, Eat…COMPOST…Repeat.  There is a poster competition, a video contest for children in 4th – 8th grade (ages 10 and up).

 Canada  The  Canadian Compost Council also has invents including a poster competition.

 Australia. CAW  has a  week of activities, events, and publicity to improve awareness of the importance of  compost, a valuable organic resource and to promote compost use, knowledge, and productsthe theme is Better Soil, Better Life, Better Future