By A.J. Bailey, Colorado Master GardenerSM, Colorado State University Cooperative Extension, Denver County
Plants and the human body have a lot in common. Among other characteristics, both need basic nutrients to keep them going.
Plants need three major and ten minor nutrients for healthy growth.
Nitrogen (N) is essential for growing strong vegetables. Nitrate is the form most readily absorbed by plants and most desirable as a fertilizer.
Leafy vegetables, such as spinach, cabbage, kale and lettuce, especially benefit from fertilizers with a high nitrogen content. Nitrogen-deficient plants display leaves that yellow from their tips toward the stem. Excessive nitrogen creates weak spindly growth, resulting in few flowers and fruits.
Nitrogen can be lost in the soil by the leaching action of irrigation and rainfall. Legumes, such as clover, "fix" nitrogen into the soil, making them excellent additions to any garden.
Phosphorus is important to early root growth, cell division and respiration. It's also necessary for fruit production. Phosphorus doesn't dissolve and move through the soil. The root tips absorb whatever phosphorus that is available, so it must be placed as near to the roots as possible to be accessible to the plant. Tuber and root crops, such as potatoes and carrots, benefit from phosphorus applications. Watch for stunted growth, dead older leaves or red or purple leaves and stems. These symptoms may suggest a need for more phosphorus.
Potassium affects photosynthesis, fruit formation and winter hardiness. Place potash near the roots in the form of humus to improve the general well-being of plants deficient in potassium. Watch for yellowed leaves or susceptibility to disease that may indicate the need for potassium nutrients such as muriate or sulfate of potash.
Calcium, Magnesium and Sulfur
Of the minor nutrients needed by our gardens, calcium magnesium and sulfur generally are sufficient in our area soils. These are important in the growth and manufacture of chlorophyll. Many of the other minor nutrients found in fertilizers actually act as catalysts for the plant to utilize or break down other food available to it.
Fertilizer comes in many formulations. The three numbers on all fertilizer containers stand for nitrogen-phosphorus-potash. Apply fertilizer 2 to 3 inches from the plant when applying at planting time. Failure to fruit and injury may result from too much fertilizer. Exercise caution when applying dry fertilizer granules. They are worked into the soil surface and dissolved with water, but they can easily burn the plant if used improperly. Liquid fertilizer may be preferable because nutrients are made available to the plant immediately.
Simple fertilizer, such as 0-46-0, contains only one of the three major nutrients. Complete fertilizers, such as 15-30-15, for example, contain portions of all three major nutrients. You also will find special purpose fertilizers available, such as rose or tomato food. And, you might want to try some of the many sticks, stakes and tablet forms of fertilizer on the market. These are compressed fertilizers that dissolve slowly as you water and yield nutrients gradually.
If you want a more natural approach, try organic fertilizers, such as bone or blood meal, manure or cottonseed meal. These are derived from the remains or by-products of once-living organisms.
Whatever method you choose, keep in mind that vegetables generally are fast-feeders. You will find tomatoes, broccoli, cabbage and celery to be among the heaviest while eggplant, horseradish and herb salsify are among the lightest. Many of our most popular garden vegetables, such as carrots, beets, garlic, onions, squash, peppers and potatoes, are medium feeders and will fall somewhere in between the two. Read the product directions carefully and pay close attention to the results of the products you try. Keep a record of uses and results.
Contact your local Cooperative Extension office for more information.
Photograph courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010