Flowers, like vegetables, are heavy "eaters" and will require nitrogen for vegetative growth and phosphorous for healthy roots and reproduction, which includes flowers. However, too much nitrogen may create a healthy, vigorous plant, with few flowers. Phosphorous is not water soluble and thus can not move easily through the soil. It needs to be placed deep enough in the soil where the plant's roots can easily take it up. Thus, it should be mixed into the soil in the root zone before planting, or dug into side trenches if required after the plant is established. If plants are in the ground, fertilizer is best applied to moist soil to help prevent burning. Because there are so many variables involved — the condition of the soil, plant species, fertilizer type (dry, slow release, liquid), weather, your garden's microclimate — there is no magic formula for applying fertilizer. Follow the directions on the label of the fertilizer you choose. Depending on your conditions, you may need to add fertilizer as often as every six weeks or so during the flowers' peak growing season. If you have nutrient-rich soil that is well prepared before planting, additional fertilizer may not be required. Consider keeping a garden journal, noting what kind of fertilizer you used, how much and when it was applied. Keep an eye on your plants. Do they look green and healthy? Do buds and flowers form? Let your plants and your "eye" determine what is needed.
Flowers grown in containers need a regular schedule of fertilizer or a timed-release fertilizer mixed in at planting time. Some Master Gardeners recommend applying a diluted fertilizer with each watering in cooler weather. In hot weather, you may need to water daily, so cut back on fertilizer to once a week. This is only a guide. The size of the container and the plants will determine fertilizer needs.
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