Making Compost in the Summer

Spring and summer is a great time to make compost. Get the manure in the spring and add extra carbon materials if needed to raise the C:N ratio to around 30:1, and put it out in windrows. Temperature should increase to over 55ºC with no problem, especially in a year like this.

There is however one other very, very important factor - water! To make good compost, the water content should be about 50-60% moisture. That is fairly easy to achieve in the spring with moist materials and an occasional rain. In a dry year like 2005, there has been no rain (in many areas) to replenish the moisture that is lost during the composting process. If the compost gets too dry, the microbes will stop working, and it will take longer to finish the compost. More importantly, if it gets too dry, spontaneous combustion can occur, which could destroy the compost and/or result in a fire hazard.

When making compost you should periodically check the temperature. During the active phase, the temperature should be over 55ºC for at least 15 days when in windrows (or 3 days if using an in-vessel or aerated system). During this time the bacteria and fungi are breaking down the carbon materials (straw, shavings, etc) to carbon dioxide, water and some other gases. Some water will go to the lower part of the pile (with gravity) and some of this water evaporates from the pile with the flow of warm air. As the compost in the top half and edges of the pile dries, the temperature increases above the optimum temperature and this kills some bacteria/fungi. Turning at this stage will help to eliminate the hot spots and the wet spots by making the pile/windrow more uniform and keep the compost process going.

You should also check the pile for moisture. The easiest way is to use a grab test. Reach into the pile in several areas and grab a handful. Squeeze it tight and then open your hand. If moisture oozes from between your fingers when you squeeze, it is too wet. If when you open your hand you see some beads of moisture on your hand but there is no excess water, it is about right. If you see no sign of moisture and the ball of compost is totally loose in your hand, it may be too dry.

When the compost is too dry you should add water to the pile. The best way to do this is to add water while turning. Some compost turners have adapters to add water while turning. This can take a significant amount of water. Irrigation over the top can help, but typically it would just put water on the top and a lot would run off, making it too muddy to turn the pile right after watering to mix it in.

Covering piles is another way to reduce moisture loss in the summer, but you still need to monitor the moisture and temperature. Covers can be fabric or a 6 inch layer of compost or straw. Plastic sheets are not suitable because the pile must be able to breathe to allow for carbon dioxide and other gases to escape, and for oxygen to get into the pile.

It is easy to put out the compost and forget it when you are busy, but stop and have a look once in a while. For more information on composting see the new OMAFRA factsheets - Agricultural Composting Basics (Order #05-023) or Manure Composting as a Pathogen Reduction Strategy (Order #05-021).

Compost turner mixing pile to distribute moisture and heat evenly.
Note the steam released from the centre of the pile

Freshly turned compost pile with moisture returned to the surface.

Learn more:

• Agricultural Composting Basics, OMAFRA Factsheet Order 05-023
• Manure Composting as a Pathogen Reduction Strategy , OMAFRA Factsheet Order 05-021

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