“The resultant worm castings need to be post-processed before it is marketed. How effective is solar drying?” Madhu
Drying wormcasts is a different issue for different parts of the world because of the climate.
Many people in hot climates will ask why anyone would want to spend time drying wormcasts when they are having trouble keeping the wormery system moist!
Where I am from the weather is cold, sun is scarce and it rains most of the time.
I have seen worm farmers having a difficult time to find a suitable place and method to dry out worm casts for packaging. Some place it in a shed for drying with heaters and fans, and some place it in greenhouses. Solar drying will also be a very effective way for drying wormcast.
Solar drying is a method used for thousands of years for drying food such as fruits for storage.
Instead of just lying the food around under the sun (where dust and pests can gather), it is placed inside a covered box, with air ventilation. The covering can be black or clear plastic, and the idea is to attract sun radiation and trap heat to speed up the drying process.
It works very much like a mini-greenhouse, but with ventilation view website. This not only helps raise temperature for drying, it also helps spread out whatever is being dried to increase effectiveness and to provide shelter from rain and pests (which is of course not a problem with wormcast).
There are more advanced machines and methods that can be bought which include fans for ventilation. A simple one can also be built by using black or clear polyethene sheets to build a tent or a polytunnel, and having both end open to allow for ventilation.
You can see a few samples of solar drying machines here.
Although solar drying itself is an effective way for drying wormcast, it also depends a lot on the surrounding humidity, wind, temperature and sun, and the higher the temperature, the more wind and sun and the lower the humidity the better.
If you are living in hotter dry climates, you can still use solar drying. However be careful not to dry out the worm completely as this will destroy the beneficial microbes within the cast. You know it is too dry… when the cast is as hard as rock.