I have a white pine sapling, which was potted for the last 6 months, in a mulch potting soil mix. Some bottom branches began to turn brown and dry, which was probably due to dry soil conditions, so i transplanted it to a larger pot, with fresh black soil. It had not grown at all in it's previous pot, yet the root systems were extensive, and clinging to the bottom of the pot. Within a week, it's bottom needles began to turn browner, but were soft. I discovered that this was probably do to a fungus in the soil. I took the black dirt from the bag I got and baked it at high temperatures, and transplanted it into another, clean pot, and washed the sapling with roots in a diluted Hydrogen peroxide solution to kill further fungus.  The root system had diminished substantially, but was about one third the length of the sapling. The photos showing the progress after two weeks. One, showing the initial dried needles on the bottom branches. The second, I took today, after transplanting yesterday. As you can see from the photo, there is substantial browning. But it's all soft, and sits outside in open conditions, with plenty of sun, or whatever conditions are outside. I know Baked soil has killed all the nutrients. What and how soon should I consider fertilizer? What do you recommend to save it? I hope you can help. Thanks, Dmitry