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How To Harvest Worm Castings Like A Boss

How To Harvest Worm Castings Like A Boss

The most frequently asked questions I get from new composters once their farms are showing signs of the fabulous compost they are so famous for is: how the hell do I best harvest the good stuff?

There are a few ways to skin this cat. For those of you not super keen on the ickier aspects of worm farming, unfortunately they usually involve getting your hands dirty. The good news is that once the worms have done their job, you are dealing with a wonderfully rich and beautiful compost that you may just feel compelled to sink your hands into!

Can you dig it? Yes you can!

Before you start, there are a few things I recommend you do to encourage ideal conditions for harvesting. Firstly, it’s worth pointing out that you can only harvest compost from about eight weeks after first feeding at the earliest –  before then your vermicompost won’t be fully processed. Choose a time when the worms have processed all the food scraps already in their bin (you can hold off feeding them for a week or so if that helps). This will ensure that you are accessing only the finished composted product rather than half processed food scraps. Secondly, harvesting will be easier if the farm isn’t too wet. A moist, loose, crumbly texture is perfect for the task (see below – think cheesecake biscuit base for a good comparison). If your farm is a little on the wet side, hold off feeding, check the drainage and station your farm in a dry place to allow some of the moisture to evaporate (if it’s not too hot, put the farm out in the sun or take the lid off for a few hours each day).


What you will need

  • A ground sheet or a few sheets of newspaper. The good thing about newspaper is that you can reuse it as bedding once the harvest is complete.
  • Daylight, or if you are indoors and working with limited light, a torch.
  • Fresh bedding (newspaper, coir, dry leaves, soil) to replenish your farm at the completion of the harvest.

The ‘Simple Dump’ method 

This method is an attractive method for those who want to minimize effort and mess. Its simple: remove half of the contents ofyour farm and disperse it over your garden. This method means you will lose a higher percentage of your worms (around half), but there should still be plenty of worms and eggs remaining to repopulate the farm in time.

Remember that the more worms you lose to your garden, the fewer you will have left and the less food scraps your worms will consume. This will be important if you have a small, urban farm and want to keep your population up so that they are able to take on a good percentage of your food waste.

The ‘Dump & Sort’ method

Dump the contents of you farm out onto a plastic sheet or newspaper and sift your worms from the castings.  You can either hand sift your way through one large pile or take it to the next level by creating multiple small pyramid piles. The little guys do not like light and will burrow down to avoid exposure. Leave your pile/s of worms in the sunlight for 10 minutes or so to allow them time to get to the bottom of the mound. Once they have done so, you are free to collect the casting from the top of each pile.  You can then return your worms to the farm with their population largely intact.

The ‘Dung Divided’ method

Work your farm in two halves. Create a regular routine of placing food scraps in one half of your farm only. Your worms will seek out the source of the food and congregate in that half of your farm. This will allow you to more easily collect castings from the other half of your farm.  Not all worms will migrate to the food, but there will be fewer to sift through when it comes time to harvest.

Once you have harvested castings from one half, swap feeding sides, opening up the other half of the farm to harvesting once the worms migrate across.

The ‘Double-the-dung’ method

An alternative to the ‘Dung Divided’ method is to get two farms running simultaneously. Feed one of the farms exclusively while allowing the second farm to process compost. You will still have to sift the fertilizer from the worm population, but it’s a good way to make sure the compost you harvest is well processed rather than cut with food scraps. Once you have harvested from one farm, switch the farm you feed, leaving the other farm to work on its compost.

If you have a multi-level farm, you can also achieve the same result through exclusively feeding one ‘level’ of the farm at a time. Again, the worms will slowly move to the source of the food leaving their castings behind them for easier collection.

The ‘Lighten-your-load’ method

Take a hessian bag or other material with holes big enough for your worms to fit through.  Spread some of the contents of your bin on top of the bag and place the bag on top of your farm. Shine a light on your worms or take them out into the sunshine. In an attempt to escape the light, the worms will burrow back through the hessian leaving a layer of castings on top.  Hessian also makes for a great worm ‘blanket’ so can be placed on top of your farm after harvest for extra insulation.

Once your harvest is complete, return your worms to their farm and add some fresh bedding. This process will give your worms a new lease on life and will bring joy to your plants!


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