I’ve decided to include two reader questions here since they are somewhat related.
Our first question comes from Hibou:
I’ve read that a bit of lime is very good for garden soil. Is it good for my vermicompost bin? If so, which type? Wikipedia tells me that “agricultural lime is” mainly calcium carbonate (CaCO3). However, the lime I’ve got my hands on is “slaked lime,” i.e. calcium hydroxide (Ca(OH)2), the by-product of acetylene gas. Thus it’s mixed with a bit of calcium carbide (CaC2) as well. What do you think? Will my worms appreciate it?
Hi Hibou – I’m really glad you wrote in with this question since this is an important topic to talk about. Firstly, yes you can certainly add lime to your worm bin in moderate amounts to help keep the pH balanced somewhat and provide a source of calcium for the worms. Is it vitally important to do so? Definitely not – composting worms actually tend to prefer a somewhat more acidic environment (similar to the one they are used to in their ‘natural’ habitats such as compost heaps etc), so you really don’t need to get hung up on the pH issue. That being said, if you ARE giving your worms a lot of acidic foods such as tomatoes or juicer waste (citrus etc), you will more than likely need to provide at least a little lime supplementation. One thing I definitely DON’T recommend you do is wait until your bin goes ‘sour’, then try to rectify the situation by dumping lots of lime in – you’ll more than likely just end up making matters worse for yourself. Rapid shifts in pH can wreak havoc on your bin ecosystem, and ultimately your worms.
Ok – now on to the different types of lime. This is REALLY important since there are a variety of different materials called “lime”. You want your lime to be CaCO3 – 95% or higher. One exception is ‘dolomitic lime’ which basically has a 50:50 ratio of CaCO3 and MgCO3 – it is ok as well. You definitely DO NOT want ‘hyrdrated lime’, ‘builders lime’, or ‘slaked lime’ (all similar) since these can be caustic and thus not worm-friendly.
Hopefully you have not added your slaked lime to your bin yet! Your worms will definitely not appreciate it.
Next, we have a question from Nick:
Are seashells (Calcium carbonate and chetin) OK to use in my
bedding, instead of eggshells or limestone? I live close to a beach full of seashells, and would be criminal not to take advantage of the millions of seashells washed ashore every day. Hopefully, there will be no adverse effects on my red Wigglers. I am a beginer in vermicomposting and would feel really bad, if I inadvertently harmed the breaders.
I am a big fan of slow-release sources of CaCO3, so I would give a big thumbs-up for seashells. I use eggshells myself, but I suspect seashells (that have been washed with fresh water to avoid adding salt to your bin, and perhaps crushed with a hammer) would provide a similar source of calcium. Moderation would be important, as always – you certainly don’t want a worm bin full of sea shell shards (try saying that 3 times fast!!), as these would likely be quite abrasive.