Important to plant health, fertilizing bushes provides additional nutrients that the surrounding soil may lack. Using fertilizer on young and newly transplanted bushes quickens plant growth and a bush's ability to establish itself into the landscape, and fertilizer helps bushes with slowing growth begin to sprout once again. All plants produce their own food through photosynthesis and the application of fertilizer provides the necessary elements and ingredients to help promote the photosynthesis process and healthy, vigorous growth.
What the Numbers Mean
Most complete fertilizers are a mix of three elements - nitrogen, phosphorous and potassium, represented by a series of three numbers, such as 18-18-18. The numbers indicate the percentage of each element in the package by weight. Therefore, an 18-18-18 fertilizer would contain 18 percent each of nitrogen, phosphorous and potassium. A 16-4-8 would contain 16 percent nitrogen, 4 percent phosphorous and 8 percent potassium. A fertilizer with 8 percent nitrogen and no phosphorous or potassium would read 8-0-0.
What Bushes Need
Nitrogen is the element most used by plants and is essential to healthy plant growth. Phosphorous promotes photosynthesis and healthy root development, and potassium assists with water retention and disease resistance. Before beginning a fertilizing program, test the soil pH to ensure the fertilizer will be effective. A soil pH between 6.0 and 7.0 is the optimum level for the bush to absorb and draw nutrients from the fertilizer. A high or low soil pH may render the fertilizer ineffective, or possibly toxic to the bush. A soil test will determine if any adjustments need to be made prior to fertilizing. Fertilize in early spring, or in autumn once the active growing period is finished. One application per year is typically enough, unless soil conditions are well-drained, sandy or if there has been a season of excessive rainfall. If so, a second application may be needed, depending on the overall health of the bush.
Also called fast-release fertilizers, water-soluble blends are dissolved in water prior to application and the nutrients immediately surround the plant when poured into the soil. Typically costing less than slow-release versions, the downside of water-soluble nutrients is their tendency to leach quicker through the soil with just a few inches of rain or additional watering, thereby not providing as much nutrition to the bush as intended. However, for a suffering bush, a quick soaking of a water-soluble blend may help its survival.
Granular, or slow-release fertilizers provide ongoing nutrition throughout the season because the granules release nitrogen and other elements over time. Place granular fertilizer in a wide circle around the bush and slightly work it into the soil surface. As rainfall or regular watering occurs, the bush receives light fertilization. Granular fertilizers are good for sloped areas, beds with high runoff or heavily compacted soils.
Natural fertilizers such as composted manure or vegetation provide the needed elements at a slower rate than other fertilizers and they also provide many of the minor elements that bushes benefit from such as iron or zinc. The nitrogen, phosphorous and potassium levels tend to be lower in natural fertilizers, therefore requiring more frequent applications than other fertilizes. The benefit, however, is that natural fertilizers aid in improving the overall soil condition and can be added to the soil at any time.
When Not To Fertilize
Poor plant growth is not always an indication of a need to fertilize. Planting in the wrong location, too much sun, not enough sun, overwatering, under watering, all can cause shrubs and bushes to have growth issues such as yellowing or fewer leaves than usual, limited twig growth or dying back of the overall plant. Before fertilizing, determine and correct the cause of the poor plant performance; the addition of fertilizer during periods of stress may cause further damage to the plant. Never fertilize when the plant shows signs of drought stress, such as scorched or drooping branches, and do not apply any fertilizers during a period of drought unless the bush is well watered. Fertilizing when conditions are dry may cause root, stem and leaf damage if water is not consistently available.
- North Carolina State Univeristy: A Gardener's Guide to Fertilizing Trees and Shrubs
- Univeristy of New Hampshire Cooperative Extension: Fertilizing Trees and Shrubs
- Sunset: Planting and Caring for Shrubs
- University of Rhode Island Landscape Horticulture Program: Fertilizing Landscape Plants
- Clemson Cooperative Extension: Fertilizing Trees & Shrubs
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