All commercial fertilizers are labeled uniformly. There are three figures. The first is the percentage of elemental nitrogen (N), the second is percentage of available phosphate (P2O5), and the third is percentage of water-soluble potash (K2O). For example, 50 pounds of (5-10-5) fertilizer contains 2.5 pounds of nitrogen, 5 pounds of phosphate, and 2.5 pounds of potash. As a rule, 10 to 20 pounds of low-analysis complete mineral fertilizer (5-10-5, 6-10-4, etc.), may be added to 1,000 square feet of garden area each year. Most Colorado soils do not require potash, so on a potash-sufficient soil, application of a high-analysis fertilizer would supply 10 pounds of superphosphate [0-(16 to 20)-0] or 5 pounds of treble superphosphate [0-(42 to 47)-0] or 5 pounds of ammonium phosphate (11-48-9) per 1,000 square feet. Nitrogen can be supplied by working well-aged manure in with the phosphate fertilizers. Note: Never use fresh manure in food gardens. Urea, ammonium sulfate or ammonium nitrate may be used at rates to give one pound of nitrogen per 1,000 square feet. Mineral fertilizers should be worked into the soil in the fall or spring. Phosphate and potash do not need to be applied after planting. Post-planting applications of nitrogen on fruit-bearing crops, such as tomatoes and strawberries, may stimulate vegetative growth and reduce yield. Starter solutions high in phosphate may be used to advantage when setting transplants. For more information on understanding and using fertilizers, see fact sheets
Choosing a Soil Amendment,
Fertilizing the Vegetable Garden,

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