I wish to make my own basic winter fertilizer. I have potash and phosphate and would like to know what else to use, keeping it nitrogen free. I also need to know how you determine the ratios of each ingredient.

Thanks to all, in advance.

It is not worth the trouble. Just buy the liqued 1-0-0, 0-1-0, 0-0-1 liquid fertilisers if you insist in mixing your own. But really. It is not worth the effort. Plants will absorb what they can use. NOt just plain what is available. A balanced green plants fertiliser is fine.

depending on where you live and the species you should not be using fertiliser in winter anyway. Deciuous trees are never fertilsed in winter. Pines only very little depending on temperatures.