Everything got wordy, so here are the highlights:
- no, don't add to active compost
- don't add borax at same time of year as lime
- yes, you can mix borax with stuff to apply it
- if you keep animals, borax can be used to improve the pasture, which improves animal health, which improves trace elements in final composted manure.
Borax is awesome for so many things. One of my favourite uses of it is as a toxic for insects like
ants. My second favorite thing to do with it is to add it as a bleach when cleaning the house - it has some great antibacterial properties. Bleach being used here in the traditional, pre-clorox company meaning of the word - whitens, cleans, &c.
Being toxic to bugs and bacteria and perhaps other beneficial beasties in your compost, makes me think it's not a great idea to add it to an active compost. Then again, I could be wrong. If anyone has evidence to the contrary on this thought, please let me know. Otherwise, I think it's a pretty solid opinion based on gathering together known facts (about borax and how compost works) and following them through to their logical conclusion.
Applying borax direct to the spring compost pile - are you also planning to add lime or other sweetener? Borax will increase the acidity of the soil, so it's not good to apply it at the same time as lime as they may interact with each other. The recommendations I've read suggests a minimum of two weeks apart in the rainy season, or two months in the dry. I usually keep lime and borax applications 4 months apart because I've noticed that closer together they seem to cancel each others benefits.
Personally, on those rare occasions when I add borax to my garden soil, I broadcast it directly, either with a seed broadcaster, or a kitchen flour sifter gadget from the second hand store. I add it after the main harvest just to the surface of the soil.
Since you are using manure... it gets me thinking what about what kind of animals you keep. Most grass munchers need trace amounts of (fancy word for borax acid - it's still pre-coffee hour here so fancy word brain retrieval system isn't working). What I do for my grazing pastures, is spread one box of borax per half acre, every 2 to 4 years. This helps keep the animals healthy, and
enough trace elements make it into the garden soil through the manure to keep it healthy.
If you can let me know your animal types I can see if I can dig up some resources that would help you learn the correct way to apply borax for your animals health. There are some very interesting works on this kind of thing.
You can mix borax with
water when applying it to the soil. Sand may work as well. If using it to kill bugs, I would mix with
DE.
One other thoughts, unless you have particularly acid loving plants or very alkaline soil, it may be better to apply borax in the fallow season, or only for emergency cases, and then to the individual plants. Then again, roses love borax any time of year.
Out of curiosity, because I always like learning about these things, how are you telling that your soil is deficient in it?