A couple of weeks ago I mentioned that I would be taking a look at the leachate that comes from vermicompost. Here is the worm house, owned by Master Gardener Meleah Maynard, from which this leachate came. This is a picture from when the house was new — it now has multiple floors.
It has been running for a few years now, and the “ingredients” that she puts in, mostly table scraps, are pretty typical of what anyone would put into compost. She reports that it produces about a gallon of leachate every 2-3 weeks. The leachate from this house has the following properties:
- pH – 8.5: That’s a high pH for soil, but for a fertilizer added every week or two it’s fine.
- Nitrogen – 1120 ppm: That’s high for a fertilizer. About twice the concentration I’d use if I were applying a liquid fertilizer to my plants at home. The nitrogen is present mostly as nitrate, which is a good thing. If the nitrogen were present primarily as ammonium, that might cause problems.
- Phosphorus – 22 ppm: That’s a good/appropriate concentration of phosphorus for most plants. It’s much less than we apply when we use a typical garden fertilizer. Potassium – 5034 ppm: This is an order of magnitude higher than we’d apply for most plants using a liquid fertilizer.
- Calcium – 279 ppm: This is a reasonable amount of calcium.
- Magnesium – 211 ppm: This is reasonable amount of magnesium.
- Sodium – 634 ppm: I’d like to see less sodium, but this shouldn’t cause a major problem.
- Other elements present included Iron, Copper, Manganese, Zinc, Molybdenum, and Boron, all at levels less than 1 ppm.
So what’s my conclusion? I think that, based on the nutrients and nothing else (no trials), this could be a great liquid fertilizer if it were used properly. I’d recommend diluting it somewhere between 1:1 and 1:5 worm juice : water before applying it, and I’d only apply it once every week or two. If you want to use it, try it on something that you’re not too concerned about first, just to make sure that it doesn’t do anything too terrible (It shouldn’t, but I believe in caution).