Flower fertilizer is composed of macronutrients, micronutrients and various trace elements.  Macronutrients are the three elements that are most needed by plants.  These are nitrogen, phosphorous, and potassium.  Nitrogen is needed for new growth of leaves and stems.  Phosphorous is needed by the roots and the bulbs that form flowers.  Potassium promotes overall health and vitality.

Primary micronutrients are calcium, sulfur, and magnesium.  Calcium helps new roots grow, and it improves the vigor of plants.  Sulfur gives leaves that dark green color so desirable in landscaping.  Magnesium, among other things, promotes seed formation and vigor.

Of all these elements, potassium is the most important because it causes flowers to bloom more.
Lawn fertilizers are counterproductive to flower gardens because they make the leafy parts of flowers greener, but they do nothing to stimulate flowering. 

The best mixtures to use in a flower garden are those that contain 17 percent potassium, 10 percent potassium, and 10 percent nitrogen.
Flowers also need extra magnesium because this will balance their greenery with their blooms.  

Flower fertilizer is available in granular form, water soluble form, and organic form.
Surprising to many, organic is the worst of the three.  It lacks many of the vital elements listed above.  With plants of any kind, you have to go by what is called the law of minimum. 

This law states that adding more nutrients already present in soil does plants no good.  Plants draw what they need in the amounts they need it, and when something is lacking, the point of lack stops their growth in their tracks.  Only by adding the elements that are lacking can you stimulate plant growth again.. 

Water soluble flower fertilizer contains all the necessary mixtures to stimulate flower growth, but it has to be continually reapplied when rain washes it away.
This is especially problematic for potassium enrichment because potassium is particularly vulnerable to rainwater and disappears very rapidly when the weather turns wet. 

For best results, then, we recommend that homeowners use granular fertilizers.  Granular products are designed for time-released delivery of nutrients into the soil.  Regardless of climatic conditions, this ensures that the necessary amounts of potassium, magnesium, and other important nutrients are consistently delivered to plants.

Before applying flower fertilizer, or even planting a flower garden for that matter, accurate soil tests must be carried out
This is necessary for two reasons.  First, it indicates which nutrients are most deficient in the soil.  Secondly, soil testing determines the pH content of the soil.  Alkaline soil content lies between 7 and 10 on a 10-point scale.  Acidic soil is anything below 7. 

Most flowering plants grow best in soil with a pH between 6.0-6.8, so anything outside of this range will need to be adjusted in order to facilitate the maximum absorption of nutrients by the flowers.

Homeowners who have the time and expertise to conduct soil testing and hunt down the best granular mix can apply their own flower fertilizers themselves.
They simply have to make certain they follow product directions to the letter, and they have to make double certain that the Potassium in the mix is going to be consistently delivered no matter what the weather does. 

Test kits for soil pH can be purchased in garden stores or online, but people should make sure the kit they are using does what it promises.

If there is any doubt, of if the homeowner does not have the time to do all of this personally, it is best to let Exterior Worlds apply flower fertilizer as part of a landscape maintenance agreement. 
We normally fertilize flower beds and flower gardens during the active growth times of spring and summer.