Most fertilizers contain nitrogen, but gardeners can choose a low-nitrogen fertilizer for soils that already have enough nitrogen or for plants that do not need very much nitrogen. Low-nitrogen fertilizers do not work great for some incredibly leafy plants, such as lawn grass. They tend to be most beneficial for plants that produce fruits, vegetables or flowers.
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Commercial Fertilizer Nitrogen Amounts
Commercial fertilizer comes with three numbers on the packaging, indicating the amount of different nutrients in the fertilizer. The first number in the ratio stands for the percentage of nitrogen in the fertilizer mixture, and the second two stand for the percentages of phosphorous and potassium. For example, a 5-10-10 ratio fertilizer contains 5 percent nitrogen, which is half as much nitrogen as phosphorous and potassium. When looking for a low-nitrogen commercial fertilizer, look for a fertilizer with a nutrient ratio that has a low first number.
Organic Fertilizer Nitrogen Amounts
Organic fertilizers, such as manure, compost, straw and leaves, also add nutrients to the soil. The nitrogen in organic fertilizers is not as readily accessible to plant roots as the nitrogen in commercial fertilizers. Before plants can uptake nitrogen from organic material, soil organisms need to break down the material and release nitrogen for the plants. To provide low amounts of nitrogen with an organic fertilizer, choose an organic material that contains lots of carbon and little nitrogen. Straw and sawdust both have high ratios of carbon to nitrogen, so they do not release much nitrogen for plants.
Nitrogen promotes foliage growth in plants. A lot of nitrogen is important for leafy plants, such as grass. Plants with less nitrogen in their soil and fertilizers will not grow as much foliage as plants with a lot of nitrogen.
Benefits of Low Nitrogen
Crops with too much nitrogen in the soil produce a lot of foliage and not as much of the actual crop. Low-nitrogen fertilizers can help plants focus on producing their fruits rather than their leaves. Veggies with low amounts of nitrogen in their fertilizers produce more antioxidants than veggies with a lot of nitrogen. Nitrogen levels can also affect the taste of plants. Although herbs grow best in somewhat fertile soils, too much nitrogen makes them leggy and less flavorful. This reduced flavor is because leggy herbs have a lower concentration of essential oils. Too much nitrogen can also cause a plant to grow more leaves than flowers.
- National Gardening Association: Soil Fertility 101
- National Gardening Association; High Nitrogen Levels Reduce Health Benefits of Veggies; Charlie Nardozzi
- Colorado State University Extension; Organic Materials as Nitrogen Fertilizers; K.A. Barbarick; January 2006
- Oregon State University Extension Service; Gardening and Water Quality Protection: Understanding Nitrogen Fertilizers; G. Andrews; January 1998
- National Gardening Association: Herb Gardening 101