Answer: Your spacing depends to some extent on how soon you want complete coverage and how long you want your planting to last. Junipers need full sun on all sides plus good air circulation to stay healthy, so you would not want to crowd these. Keep in mind that sometimes you can do a group planting or island planting rather than a stright line to provide screening, and this might allow you some leeway in spacing. Ideally they would be eight feet or more apart, but this will take years for them to begin to grow into a dense screen. If you plant them closer together they will screen faster but may not be as long lived. It is a matter of personal preference. You might also consider using a different plant that is more amenable to hedge type use.
Fertilizing is not usually recommended for new plants. It is more important to dig a wide hole and loosen the soil over a generous area to encourage easier rooting. If you use an organic mulch year round, this should provide enough nutrients gradually as it breaks down. The bonemeal is very slow acting. You could also top dress each spring with good quality compost and possibly a general purpose granular fertilizer such as 10-10-10 per the label instructions. It is better to underfertilize than overfertilize and junipers as a group do not require a rich soil to grow well.
I hope this helps.
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