Purpose of a bottom container beneath a worm farm

Question

I followed a video on building my own worm farm using styrofoam boxes. The video suggested having a box underneath the main box to collect the worm castings, so it required I put holes in the base of the main box and have an empty box underneath.

The instructions also suggested placing fly screen at the base of the top box to stop worms leaving and other insects from infesting from below.

I have added my worms and everything has been going smoothly and the worms are processing a large tub full of scraps every week, however the lower box is completely empty?

The boxes I am using are about 1 - 1.5 foot deep. I filled the top box with about 3/4 of soil.

I am wanting to know:

• Is the bottom box even necessary if I stack a box on top once the bottom one is full? I can empty out the bottom soil and use in the garden etc, right?
• If it is a good thing to do, is it maybe either the fly screen or I put in too much soil to start with?
• Was it even necessary to put that much soil in to begin with? I am curious because when the container is completely full and I add a top container do I need to semi-fill it with soil?

Answer 1

• An extra box below a main box with holes can be used for 2 purposes:

  1. Capturing fluids. The holes make sure that a surplus of fluids can escape and your box doesn't get too wet. Holes used for draining only are usually small.
  2. Harvesting compost. When using a continuous flow approach (a.k.a. flow-through approach), you regularly remove compost that is ready to be used from the bottom of your box. In this case there are usually large holes or a mesh at the bottom of your box, optionally with a bar for scraping. More info on different continuous flow systems here.

  If you use a stacked approach and have a good method of draining fluids (e.g. a tap), then an extra box below your main box is not necessary. Like you said yourself, if you stack you can empty the bottom box once the worms have moved to the upper box.

• Your approach seems fine. Just make sure the conditions in the bin remain ok (not too wet and not too dry). When you start composting, you can add a little bit of soil so the worms have some space to roam around. There is no need to start a bin with lots of soil but it won't harm the worms either.

• Your third question has already been answered here. There is no need to add new soil when adding a new box on top.

Answer 2

I think you have ample soil, and that soil is still filling up with castings. But if it's been a couple of weeks and you're not seeing anything, your worms are probably too dry.

In Australia it's often necessary to water your worm farm as the heat dries them out too much. It's like a pot plant - you have a small amount of soil that doesn't have the thermal mass of your garden, so it gets hotter and colder than the ground does. The polystyrene helps, but when it's really hot (as it has been lately) the soil can dry out.

You should have newspaper on the top to reduce evaporation. Lift that up and poke around. The active part of the worm farm should be moist. Not soaking wet, but squelchy and moist. The paper on top should be soaked, though, and that will dry out over time. Like many insulation setups, this is all about layers. You have a layer of wet newspaper, then a layer of moist air above it, then the lid of the worm farm, then hot, dry air. Well, "air that's not cool and wet", because it's cool, wet air that worms like.

Normally vegetables have enough water content that this isn't an issue. But in hot dry weather like Melbourne heatwaves (days of 45°C with 10% humidity) we were watering our worms twice a day, and they were still trying to escape the heat.

That water is what percolates through and gives you "worm juice". If you're not getting that I suspect your worms are too dry.