Just because the soil looks rich and dark doesn't mean that the nutrients are all there. Soil nsoil test tells you what's already there (so you don't add more) and what's missing. Lime is used for raising pH (making it more alkaline). Sulfur lowers soil pH (making it more acidic).
Slow-release fertilizers are excellent to use at planting time. Advantages of slow release fertilizers are that the nutrients are available gradually over time. This means that the gardener can fertilize less often and the nutrients are provided slowly and steadilly. This is how most plants prefer to be fed and helps them grow well. Most slow release fertilizers (organic and synthetic) release at specific (warm) soil temperatures. The benefit of this is that plant roots generally are most active in warm soil and therefore the slow release fertilizer will start to make fertilizer available as soon as the plants actually needs them. As the plant roots become more active (in warmer soil) more fertilizer will automatically be released.
Follow the manufacturer's directions carefully as to the size of the plant to be fed and the exposure to sunlight.
For plants with limited nutrient needs, time-release fertilizers may be enough to support the plant throughout it's life. For others, subsequent applications utrients can become depleted over time and need a boost. A soil test is the key. The