I generally empty mine when the top layer is almost full (generally twice a year with my family) and I try and do it in the Spring and the Autumn i.e. while the weather is still reasonable.
A common misconception is that all the worms will have vacated the bottom layer and moved up. I've owned a wormery since 1998 and I have never yet known this to be the case - there are always a few of the stubborn ones quite happy in the bottom layer.
So how do you separate them from the compost?
You have a few choices:
- The first is don't bother. You can just empty the whole bottom layer in your border or compost bin where the few stragglers and eggs will either live in the garden, become live food for the birds or in the case of the compost bin carry on regardless. I like the last option because they can then colonise your compost and thereby speed up that process as well.
- You can empty the whole lot into a barrow or onto a plastic sheet and hand pick them out, either adding them to your wormery again or even box them up and head off fishing. The choice is yours.
- Put the bottom layer on the top with the lid off. Scrape away and remove compost until you come across some worms and then leave it for a bit. Worms hate the light and will burrow down into the compost that remains. Repeat this process until they have all burrowed into the layer below, by which time you will have harvested all the compost.
Be warned though that this is a lengthy process.
When you remove the bottom layer you will almost definitely find that the sump is full of worms. Many beginners panic and worry about worms getting in the sump but they always do.
It's yet another reason to make sure you empty the sump regularly so that they don't drown.
They can and will climb out when they are ready but you're very lucky indeed if you never find any there.
As you can see from the pictures both my bins have plenty of worms in the sump. So while we're emptying the bottom layer make sure you empty the contents of the sump (drain it of liquid first though) into the top layer. It tidies the sump up as well as helping establish worms in the new top layer.
So now you've emptied the bottom layer and cleaned out the sump you can place the now empty tray to the top of the bin.
When adding this new layer be careful to make sure that it fits snugly. If there's too much stuff in there then a) you'll be squashing them with the new one and b) they can get out of the sides.
I just add the layer and start adding waste - they will move up when they are ready i.e. they have eaten most of the layer below and fancy some of the new stuff.
I guess it wouldn't harm to take some of the bottom layer and add it to the new one, especially if it's quite full and stops the new layer fitting snugly. Definitely add the moisture mat (or a layer of cardboard) as the darkness will further attract them into the new layer.
As you can see from the pictures, adding what's in the sump can make the wormery look quite wet and soggy so make sure you add a fair amount of shredded/scrunched paper and/or cardboard to help dry things out.
You can never have enough paper in a worm bin, something that people often forget. It helps keep things dry and adds a god dose of carbon. The worms will munch their way through it as fast (if not faster) than the food scraps and the resultant compost will be of a higher standard.