Common Mixed Fertilizers

Fertilizer Grades

• Commercial fertilizer formulations follow a national standard, known as a grade, that is displayed on product labels. Three bold numbers on the label represent the primary nutrients nitrogen, phosphorus and potassium and in that order. Although fertilizers with only one nutrient are available, mixed fertilizers contain at least two primary nutrients. 10-10-10 is an all-purpose, fast acting grade to give plants a quick boost. Other readily available mixes include 5-10-5, 5-10-10, 8-0-24 and 6-6-18. If you need to know the weight of a nutrient in the fertilizer mixture, multiply the bag's total weight by the percent displayed on the label. For example, to determine the number of pounds of nitrogen in a 50 pound bag of 8-0-24 fertilizer, multiply 50 by 8 percent or .08. Synthetic commercial fertilizers contain more filler than nutrients, which can help you spread the mix evenly.

Soil Test

• Obtain a soil test from a commercial service or local university extension to determine the amount and type of fertilizer needed. Although home soil kits are available, professional services are more accurate. Test results will also list macronutrient content and pH levels. Re-test every four to five years for current nutrient levels because the soil's needs change over time. Fertilizer is applied more heavily right after a soil test, but once basic fertility is achieved, nutrient applications are applied more lightly and may include a seasonal side dressing of nitrogen or other needed nutrients. Sometimes unusual fertilizer mixtures such as 15-0-14 or 8-0-24 may be recommended for soils high in phosphorus. Contact a fertilizer dealer who works with farmers if these blends are not available at local garden centers.

Synthetic Mixtures

• Synthetic fertilizers, the type of fertilizers most often found in garden supply centers, are usually granular and water soluble, allowing for the quick uptake of nutrients via roots. Synthetic fertilizers may be manufactured from a combination of organic and inorganic sources. Most synthetic fertilizer mixes do not contain micronutrients. Products containing micronutrients can be purchased separately and according to which elements, if any, the soil test shows are missing.

Organic Mixtures

• Many retailers now carry organic fertilizer formulations. These mixtures release nutrients at a much slower pace than synthetic formulations, but contain micronutrients and are compatible with organic gardening. As with synthetic mixtures, levels of nitrogen, phosphorus and potassium are listed on the organic fertilizer labels. Although many organic fertilizers also contain micronutrients, these concentrations vary widely from bag to bag. Organic fertilizers with a comprehensive level of nutrients include fish emulsion, bone meal, bloodmeal and manure.