Inoculating biochar has nothing to do with needles and everything to do with filling up some of the porous spaces, of which there are MANY, in your biochar. Sometimes this process is referred to as ‘charging’. Really it just means mixing!
Biochar added to soils all on its lonesome can actually create a not-so-great scenario underground in the first year. That’s because its hungry to fill in its spaces (think of an apartment building needing furniture and people!). If it doesn’t have something already filling that space, it will slurp up nutrients and water from surrounding plants and soils. So really its best it inoculate/charge/fill up/mix before you apply it. A lot of research says you should do this at least 2 weeks before you mix it into your soils.
There are lots of options in terms of what to mix it with; compost, compost tea, manure, and even (gasp) fertilizer can be used. It really depends on what your soils and/or plants need most. One rather interesting approach is to use biochar in your composting toilets (c’mon, you’ve got one, right?). All that ‘material’ added to the biochar – which also helps with any unfortunate odors – will actually provide a rather high degree of nitrogen. Adding this to food growing soils might be a bit of a marketing challenge however. An easy way to inoculate your char is to toss it into your compost bin – this also helps cook the compost faster and acts as a deodorizer as well.
The ratio of your mix is mostly up to you. A 25/75 blend by volume (biochar/compost) is often recommended but a mere 10% biochar tossed in a high quality crumbly compost pile can work wonders. Test it yourself to see what works best with your soils and plants.