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Fertilization at planting and during establishment
Adding slow release fertilizer of any type at planting has never been associated with improved or reduced survival. There are only a few documented growth increases associated with fertilization applications made at or soon after planting (Gilman et al. 2000). Response to fertilizer applications at planting is most likely to occur in poor soils, and response is likely to be minimal.
Application of slow release fertilizer is not likely to hurt the plant provided it is applied according to the directions on the product. On the other hand, adding soluble fertilizer to a newly installed plant could burn roots if too much is applied. Burned roots will injure the plant and could kill it under some circumstances.
Since survival will not be improved, growth increases are unlikely (except in very poor soils), and the potential for fertilizer burn is real, it might be best to make the first fertilizer application at least a few months to a year after planting. Any nitrogen source can be applied to established trees with about the same effect on the tree.
When fertilizer is applied, spread it on top of the root ball and backfill soil or on top of the mulch. There is no need to mix it with the backfill soil or place it at the bottom of the planting hole since most roots end up close to the soil surface in urban and suburban landscapes. Under most circumstances, mulch will not steal the fertilizer from the tree (Gilman et al. 1990).
Read more on details of fertilization and transplanting.
See: University of Florida landscape fertilization best management practices.
