What kind of fertilizer should I use for Redwood trees?

Answer 1

Redwoods can be fed with a fertilizer for acid loving plants, they like a pH that is on the acid end from 4.5 to 6.5 in the usual sandy loam. A ratio of 3-1-2 is a good basic number for trees or lawns.
Plants benefit from a slow release nitrogen fertilizer that may be organic or inorganic. Keep in mind that nitrogen is readily leached (washed through soil) but phosphorus and potassium are not, meaning they require less frequent application. Look for water insoluble nitrogen (WIN) on the label. The higher the WIN number, the longer lasting and the safer for the environment the fertilizer will be.
Fertilizer application needs to be more frequent in sandy soils, but with lower rates each time due to leaching potential of sand.
Fertilizer rates for trees are no longer based on trunk size or caliper, but on root system spread, calculated by doubling the area of crown coverage (crown coverage = 3.14 x radius^2). Use one to three pounds of actual N/1000 ft2 of root zone or less if the tree is restricted in growth as in a pot or near building.
Apply fertilizer Valentines, Labor, & Christmas days or spring , fall & winter when water is available in the soil. N-P-K ratios should be 3-1-2 or 3-1-1 or a multiple of those like 6-2-4 if you use a complete fertilizer. This is a typical lawn fertilizer ratio like Season Lawn Fertilizer 6-2-4
Compressed spikes only work when the soil is moist and soft.

Fertilization will not benefit a plant under stress from compacted or water saturated soil, insufficient light or space, or excessive pest problems.

Answer 2

I probably would put fertilizer spikes around the tree. You can get them for evergreen trees.