Answer: All plants need nitrogen, phosphorus and potassium for healthy growth. Some plants have specific needs which are often addressed in specialized fertilizers such as those formulated specifically for roses or for rhododendrons/azaleas. These contain additional elements and are tailor made for roses or rhodies. Nitrogen promotes lush, green growth; phosphorous promotes flowering and healthy stem growth; phosphorous works in conjunction with the other two and encourages healthy root and stem growth. If you have a shrub that flowers, you'll want a higher middle number, which will promote flowering.
In a nutshell, homogeneous blend fertilizers are those that, through the manufacturing process, contain equal amounts of all elements contained in the fertilizer. This manufacturing process ensures that each pellet is exactly the same. Simple blend fertilizers can contain the same elements as a homogenized blend but each element is separate (you can see the individual granules of different fertilizer materials) where the manufacturer has mixed particles together to produce a desired overall composition. Water soluable fertilizers can be used as foliar feeds, are quick release and generally will not burn plants the way granular fertilizers can.
How often you feed depends upon the particular plant you are growing. The fertilizer labels will recommend how often to apply.
Hope this answers all your questions!
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