Fertilizer Labeling
The numbers on any bag of fertilizer refers to the volume/percentage of primary nutrients found inside.
The primary nutrients in fertilizer are:
- nitrogen (N)
- phosphorous (P)
- potassium (K)
- N-P-K
Primary Fertilizer Ingredients
The first number is the percentage of nitrogen in the fertilizer bag. So a bag of 5-15-5 has 5% total nitrogen, 15% Total phosphorous and 5% Total Potassium. That’s 25% – the remaining 75% are other nutrients and filler product. This filler helps to distribute the nutrients evenly – The filler is also essential, as adding only nitrogen, phosphorus and /or potassium could chemically burn the plants. . Other nutrients include calcium, magnesium, sulfur ,iron, and organic matter.
Nitrogen in fertilizer increases a plants ability to produce chlorophyll, the end result being rapid growth and darker richer color. That’s just dandy if you want a luxurious dark green lawn that needs a lot of mowing. But Be aware that if you are planting fruits and vegetables excessive nitrogen will lead to rapid plant growth and dark richer foliage AT THE EXPENSE of fruit/vegetable production. Plants that are deficient in nitrogen may start turning light green or yellow.
Phosphorous is the second number in the mix. For example, 5-15-5 has 5% total nitrogen, 15% Total phosphorous and 5% Total Potassium.
Phosphorous in fertilizer aids in root development and increases flowering ability as well as bloom size. Some high phosphorus fertilizers are marketed as ‘Bloom Buster‘ High-phosphorous fertilizer should be used when plants are being established in your garden.
Potassium is the third number, it represents the percentage of potassium found in the product. So a bag of 5-15-5 has 5% total nitrogen, 15% Total phosphorous and 5% Total Potassium.
Potassium in fertilizer helps guard against many plant diseases, it’s a botanical immune system booster. It aids in drought and cold tolerance. It also helps in the process of photosynthesis and in improving root development . High potassium fertilizer is a good end of season fertilizer during the summer it can be used to protect from temperature extremes or when insects and or disease has damaged plants. You can also get fertilizers that contain single primary nutrients such as Ammonium Nitrate and Sodium nitrate {Nitrogen}
Secondary Fertilizer Ingredients and Trace Elements
Calcium {Ca} When calcium fertilizer is used it lowers the pH of the soil reducing the toxicity of the soil. If it is applied beyond the requirements it will stimulate the ammonium absorption by plants by as much as 100%. Calcium is represented as “Ca” on fertilizer labels. Crushed/ pulverized eggshells are an excellent source of Calcium for gardens.See: Eggshells as Fertilizer
Magnesium {Mg} Magnesium is the central element of the chlorophyll molecule and is essential for photosynthesis, as well as Sugar synthesis and the plants Nutrient uptake.
Plants such as blueberry, beets, broccoli, cabbage, cauliflower, celery, corn, cucumber, eggplant, lettuce, onion, pepper, potatoes, pumpkin and squash, spinach, tomato, and watermelon respond very well to increased Magnesium . See: Epsom Salts as fertilizer
Sulfur {S} Some vegetables have high sulfur requirements that is not routinely met by garden soils or standard fertilizers. Asparagus, Cabbage, cauliflower, kale, onions, radishes, turnips and many flowering plants need a lot of sulfur to thrive. If they are not getting enough sulfur from the soil, they will develop signs of sulfur deficiency. Sulfur fertilizers include sulfate of potash, ammonium sulfate and composts or manures.
Gypsum (0-0-24) has been widely used for many years as a sulfur- and calcium-bearing material for fertilization and soil reclamation. It is a neutral salt and has no effect on soil acidity in our soils. You can also address sulfur deficiency with using Epsom salt.
Epsom salt is actually magnesium sulfate, The effect it has on plant growth is largely dependent on what kind of soil the plant is growing in.
Other ingredients include copper, iron, boron, zinc, chlorine, cobalt.