Commercially available fertilizer mixes are designed to supply the correct ratios of nutrients for garden plants. The three main ingredients contained in mixed fertilizers are nitrogen, phosphorous and potassium. This is expressed on packaging as the N-P-K ratio. As with all garden chemicals, common mixed fertilizers should be stored out of reach of children. Once the fertilizer is diluted and applied, most treated plants are safe for children to play around. Check package labels for specific warnings.
What Is a Mixed Fertilizer?
There are three main types of fertilizers: straight, complex and mixed. Straight fertilizers supply one type of nutrient. Complex fertilizers are a single substance that supplies more than one nutrient. Mixed fertilizers combine more than one type of straight or complex fertilizer to give plants a specific mix of nutrients. Purchasing mixed fertilizers saves time and effort, since individual components of fertilizers do not have to be researched and mixed by hand. Commercially available mixes are balanced to provide the right amount of each nutrient, and often contain micronutrients that would be harder to mix at home.
The main ingredients in all-purpose fertilizers for use on gardens and potted plants are chemical or natural sources of nitrogen, phosphorous and potassium. A water-soluble plant food with the ratio 24-8-16 contains 24 percent nitrogen, 8 percent phosphorous and 16 percent potassium. The remainder of the mix is filler or trace nutrients. One tablespoon of this fertilizer would be mixed with 1 gallon of water and applied every seven to 14 days when plants are actively growing. A time-release fertilizer to be worked into the soil every three months will have a different fertilizer analysis, such as 10-10-10.
Mixed lawn fertilizers are typically sold in granular forms or as liquids that are applied when irrigating. For granular fertilizers, apply according to label directions, using a drop or cyclone spreader. Apply half the amount of fertilizer in one direction across the lawn, and then spread the remaining fertilizer in the other direction to avoid missing patches of lawn. Liquid fertilizers are often sold in a bottle that attaches to a garden hose and automatically dilutes the fertilizer as the lawn is watered. Lawn fertilizers contain high percentages of nitrogen and low levels of phosphorous. Typical ratios include 32-0-4 and 29-2-3.
Special Plant Foods
Different types of plants have different fertilizer requirements. A time-release food for shrubs might have a fertilizer ratio of 18-6-8 with traces of minerals like magnesium, copper and iron. Rose mixes contain higher amounts of phosphorous with similar proportions of nitrogen and potassium, such as a 9-18-9 or 18-24-16 ratio. Vegetables can usually be fertilized with all-purpose plant foods, although there are specific mixed fertilizers for a few plants. Tomato food, for example, has a fertilizer ratio of 18-18-21 and can be used on other vegetables as well.