What Is the Best Fertilizer for Beans?

Fertilizer Formulas

• A bag or box of fertilizer will have three numbers prominently displayed, such as 20-20-20 or 5-10-10. These are the NPK numbers, standing for nitrogen, phosphorous and potassium. Nitrogen promotes leafy growth while phosphorous and potassium both contribute to strong stems, abundant flowers and healthy fruit development. Vegetables, including beans, need a constant supply of nutrients to grow well so fertilizing both before and after seeding is important.

Fertilizer Needs of Beans

• Beans are light feeders, needing less fertilizer, for instance, than corn. The most accurate way to judge the need for nutrients is to have a professional soil test done to find out the amount of nitrogen, potassium and phosphorous present in the soil. Home test kits are available, but may not be as accurate.

  Without a soil test, you can simply mix a low nitrogen fertilizer such as 5-10-10 into the top 6 inches of soil before you plant. Higher levels of nitrogen will delay flowering and pod formation. Sandy soils may need another application of nitrogen fertilizer after a good set of pods since nitrogen leaches more quickly in light soil.

Inoculating the Seeds

• Since nitrogen is easily leached out of the soil, it is the most commonly lacking nutrient. Nitrogen-fixing bacteria will contribute this element once a good root system is established but, if a legume has not been grown in that soil before, you'll need to inoculate the seed to make sure bacteria is present near the developing roots. Packets of the inoculant will be available wherever you buy bean seed.

Micronutrients

• Beans and other plants need nutrients other than nitrogen, phosphorous and potassium. Some, like calcium and magnesium, are used in moderate quantities or are usually present in the soil in sufficient quantities. Others, called micronutrients, are needed in very small amounts. In general, micronutrient deficiencies are not a problem in beans but a deficiency of zinc may cause stunting of young plants and some yellowing of the leaves.