Aside from purchasing a test kit, learning how to test compost for maturity is easy. Garden composting is collecting waste material from the garden or kitchen and letting it decompose to use as a fertilizer. Compost must mature before it is ready to use. Immature compost will kill your plants, because it will siphon off valuable oxygen that the roots need. You can conduct your own test using some simple supplies.
Step 1-Label Your Containers
Divide your containers into two sets of six. Label the first six containers with the date you plan to begin your test, the word CONTROL, and number them consecutively from one through to six. Label the second six containers the same way, but instead of the word control, use COMPOST.
Step 2-Get Dirty
Fill the six containers that you labeled as CONTROL with the potting soil and fill the six containers you labeled COMPOST with your compost sample.
Step 3-Plant Your Seeds and Place Your Containers
Plant 6 seeds into each container and water them. Place the containers in various spots about your room or nursery.
Step 4-Water and Wait
Over the next seven days, water each container to maintain moisture.
Step 5-Count Your Germinated Seeds
After the seventh day, count and record the number of seeds that germinated in each cup. Put those numbers in a chart.
Step 6-Do the Math
For the control group, divide the number of germinated seeds in one container by the total number of seeds used in all 6 containers and multiply that number by 100. This number will give you the germination percentage. Repeat for all six containers. Then repeat the entire process for the compost group.
Step 7-Compare Your Results
If the germination rate in the compost group is significantly lower than the control group, your compost is immature. If the germination rate is equal to the control group, then your compost is ready to use as fertilizer.
Repeat this process again after the compost has aged another 21 days if your compost is immature. If you do not wish to use any mathematics, there are two simpler ways to test for maturity:
Get two pots and put samples of the compost into each pot. Plant five to seven radish seeds into each pot. If ¾ of the seeds germinate, then your compost is mature.
Get a handful of compost from the middle of the compost heap and dampen it. Place it into a plastic bag and seal. Keep the bag for seven days at room temperature. Open the bag and smell the contents. If the compost smells pleasant and has an earthy smell, then the compost is mature.
Testing your compost will ensure quality fertilizer and a healthier garden.