Proper fertilization of flowers growing in landscape beds is important to ensure that annuals perform well all season long, and perennials are more likely to repeat bloom year after year.
Annuals Flowers. Annual flowers are grown to provide flower color and/or foliage interest all season long. Most annuals will continue to bloom if their needs of water and nutrients are met, until plants are killed by fall temperatures. Some also benefit from removal of old flowers (deadheading). The most important nutrient needed in most Kentucky landscapes is nitrogen. A soil test will indicate if other nutrients are needed. When annuals are installed in spring, about ¼ pound of actual nitrogen is added per 100 square feet of planting area. If you use a high nitrogen fertilizer such as 46-0-0 or 33-0-0, that would be around ½ to ¾ cups of these fertilizes worked into the soil at planting. Then annuals need additional fertilization—apply about half the previous rate monthly through September. There may be time for more one fertilization in late summer this year to help ensure blooms until frost. When applying fertilizer to established plants, spread it on the surface of the soil and lightly cultivar and/or water the fertilizer in. Wash off any fertilizer that may adhere to foliage. Alternatively, you could apply compost to your planting. It would be best to begin the season with a good application of fertilizer since the compost releases nutrients slowly, but the nutrients released by the compost should provide for the needs of the annuals for the rest of the growing season. There are also slow release fertilizers that supply nutrients over a 3-6-month period, or you may choose to add fertilizer in a water soluble form through irrigation or the watering can. In either case, consult the product label for proper application rates. If you are adding fertilizer but not ensuring good soil moisture you are wasting your time and money. Ensure annual plants are well watered during dry seasons.
Perennial Flowers. Perennial flowers are a bit different than annuals. They generally require less fertilization and since they often slow down growth in autumn to prepare for dormancy, fertilization should be avoided after late summer. Also, some perennials bloom early in the season and often go dormant in later summer and need less fertilization. The initial fertilization rate for perennials should be the same as that for annuals given above. This is usually applied in early spring as perennials are beginning growth. For early flowering perennials (spring flowering bulbs, peonies, columbine, bleeding heart, etc.) this may be all the fertilizer they need. Later blooming species such as asters, goldenrod, chrysanthemums, will benefit from one or two additional applications of fertilizer, about every 6 weeks, or application of compost. There still may be opportunity to fertilizer some of these species this summer. Let the plant tell you when to stop fertilizing. For perennials, once blooming has been initiated, stop fertilization and don’t fertilize again until next spring. Unlike annuals, most established perennials can withstand several weeks of dry weather without rain. However, this does not mean they will perform well under these conditions. If you are fertilizing, make sure plants are well watered as well. Neither annual nor perennial plants are able to take up nutrients from dry soil.
Submitted by Rick Durham, Consumer Horticulture Extension Specialist