Question
Hi.  I have been trying to make my own organic fertilizer.  It contains worm castings, guano and humate.  After a few days it smells musty and looks like little white mold spots appearing on the surface.  What is causing this and is the fertilizer safe to use on my plants?

Answer
Taken literally, organic 'fertilizer' is a bit of an oxymoron.  Traditional fertilizer tries to send minerals directly into the plant bloodstream, like vitamin pills.  There are negative side effects with this method (risk of overdose, decimation of microbes, buildup of salts).  But when it was invented 100 years ago, it was expected that fertilizer would bring intensive farming to a whole new level and boost output of food manyfold.

Without fertilizer, plants are stuck with whatever's in what they're growing in.  They can't get up and leave a poor location.  If they sprouted in Sand, they're stuck with it.

The problem for them is not so much that Sand is, so to speak, a desert when it comes to macronutrients.  The problem is that there are no microbes to turn the raw material into the kind of food the plants can eat.  

Along comes organic farming.  Instead of those outdated chemicals, people are going back to the basics.  Because scientists have learned that microbes break down Soil and deliver it to plants on a silver platter.  They can track these delivery systems with supermicroscopes and other high tech methods.  They can identify some, although not all (not yet anyway), of the participating microbes.  The concept of organic fertilizer is actually a food delivery system that 'farms' those specialized, beneficial microbes.  They break down the food, metabolising it, and then deposit it near or, frequently, into the roots of a very happy plant.

So you see, your organic fertilizer is really a way of making microbes comfortable enough to generate nutrients.  That's why 'organic amendments' are such a great idea.  Organic amendments are a free lunch for beneficial microbes that will transform them into something delicious and nutritious for plants.  The white fungus/mold you see is just one kind of microbe, and it's doing exactly what you need: It's turning some of those raw materials in your compost into a plant-friendly 5-star dinner for any plant you choose to grow in it.

True, you have to be careful with these things.  If you were out in the garden, you might mix it up with a disease causing microbes.  But I doubt that's the case here.

Let's talk about that odor.

Anaerobic microbes -- the ones that thrive without air -- often do cause disease.  This is why it is so important to make absolutely sure you have lots and lots of Oxygen in any compost.  You want to feed the Aerobes, starve the Anaerobes.

Don't use any fungicide or other chemical, organic or otherwise, on this material.  Let it fully cycle.  Depending on the substrate, it will be available in weeks or, worst case, months.  The usual composting guidelines apply.  Thanks for writing.

THE LONG ISLAND GARDENER