I keep a vermicompost bin and I sometimes worry that I haven't given the worms enough food or if it's not wet enough. How can I keep track of the worm's general health?
If the worms are growing (dig down and check on this every now and then), eating (new food should disappear from the surface in just a few days), pooping (leaving casings on the top of the worm bin soil) and reproducing (really healthy bins get so full of worms that some of them need to be "re-homed" on a regular basis), then they are doing well. If food left on top doesn't show signs of being eaten, if the worm bed smells, or the worms stay small and don't multiply, then you need to check on how you are feeding them and how warm and moist the contents of the worm bin are.
A general rule is if you dig around carefully in your bin and you see worms of all sizes, ranging from tiny baby worms to large adult worms, as well as worm cocoons (small white-brown eggs that look like seeds), then the worms are procreating fine and should be ok and healthy. Just don't check this too often, because worms don't like to be disturbed. Other clues that you are doing ok are:
- bin has an earthy smell
- worms have a glistening skin
- there is sufficient air in the bedding
- bedding is disappearing over time
- worm castings are accumulating
A clue that something is wrong is if you only see adult worms, or if worms are trying to escape your bin (unless you have a dark bin where the walls get moist, then worms may try to escape even if conditions are fine). Other bad clues are:
- bin is smelling sour
- worms look dry
- material is becoming a soggy clump, leaving little air for the worms to breath
- one particular critter species seems to be taking over the bin (e.g. fruit flies, mites, maggots, ants).
Moisture: To check the moisture level, take a bit of material from the bin and squeeze it in your hand. If one or two drops of water come out then it is just moist enough (for most worm types). If more comes out, your bin is probably too wet. Another clue that the bin is too wet is if it is starting to smell sour. Some worm types such as the Eisenia Hortensis like it a bit more wet. Personally I almost never add water because my kitchen scraps will contain enough water already and my bin will retain that water very well (because it's plastic).
Feeding: How much food to give depends on a lot of factors. How many worms you have, the available surface in your bin, the temperature in the bin (below a certain temperature worms stop eating), the type of food. Worms won't eat fresh scraps immediately (they don't have teeth), instead they suck up the parts that are decomposing. If you see a lot of decomposing or still fresh-looking food then don't feed them yet. Wait until it has disappeared a bit.
A good strategy for feeding is to create several 'pockets' in your bin. Fill a pocket with food and check if the worms are starting to eat from it. As soon as they do, start filling another pocket.
BTW, if you really want to keep your worms healthy, try to feed them organic foods as much as possible. Many non-organic fruit and vegetables contain pesticides that are bad for the worms and the microorganisms in the compost.