When you walk down the fertilizer aisle at the nursery or home improvement center, you'll likely notice the array of formulations. You’ll see bags, bottles, powders, granules, sprays, and concentrates. Furthermore, you’ll discover an increasing number of organic and “earth-friendly” fertilizers. Learning more about your options can help you pick the best flower food for your plants.
For most flower gardeners, a complete fertilizer is necessary to supply plants with the three major elements they require to thrive:
- Nitrogen (N): Promotes healthy foliage
- Phosphorus or Phosphate (P): Stimulates root systems
- Potassium or Potash (K): Aids in flower (and fruit) formation
The fertilizer label will list these nutrients in order (sometimes referencing them as "NPK") with numbers representing the percentage of a nutrient compared to filler ingredients. For example, 10-10-10 fertilizer contains 10 percent of each nutrient. Filler ingredients are inert materials that add weight and volume, like limestone, sawdust, clay (in powdered formulas), or water (in liquid fertilizers).
Flower fertilizers usually have a larger percentage of phosphorus compared to other ingredients. Healthy flowers start with vigorous root systems, and a phosphate boost can ensure your flowers get a good start.
Fertilizer manufacturers create artificial fertilizers by combining inorganic chemicals to form compounds like ammonium nitrate or magnesium sulfate. Some advantages of chemical fertilizers are that they're inexpensive, readily available, and rapid-growing plants like annual flowers take up the nutrients quickly (unless the formula is designed to be a time-release fertilizer). Disadvantages include the risk of over-application, which causes burning, and the absence of any soil-improving qualities.
Chemical fertilizers come in a range of formulations, including pellets, liquid concentrates, and powders. Some products come in pre-measured packets designed to be added to the watering can, making it convenient for gardeners to apply it to containers, houseplants, or their landscape.
Foliar fertilizers are liquid nutrients that plants absorb through their leaves. Not all flowers feed efficiently this way, because the waxes and hairs on leaves act as a barrier to nutrient uptake. Flowering plants cannot receive all of the nutrients they need through their leaves, but you may address some nutrient deficiencies quickly by using foliar fertilizers. Potassium is one readily absorbed nutrient in foliar feeding applications, so use foliar fertilizers in the flower garden to address potassium deficiencies.
If your flowers are exhibiting signs of chlorosis, such as a yellowing of the leaves, your plants may have an iron deficiency. Sometimes, the rapid results achieved by foliar fertilizers can help.
Organic fertilizers come from living things, like animal manure, fish emulsion, leaf molds, and non-living things, like rock phosphate or greensand. Fertilizers from organic matter not only supply essential nutrients to flowers, but they also improve soil tilth. Gardeners who don’t eat what they grow still appreciate organic fertilizers because they:
- Don’t burn plants
- Strengthen plants’ immune systems
- Are non-toxic to beneficial insects and wildlife
- Remain active in the soil for long periods
Disadvantages of organic fertilizers include their higher cost, taste appeal to some pets, and limited formulations. Organic fertilizers are not an overnight fix—they won’t correct severe nutrient deficiencies quickly.
If a soil test reveals a deficiency of one major nutrient, you can purchase a simple fertilizer, which contains only nitrogen, phosphorus, or potassium as a standalone ingredient. Simple fertilizers can be chemical or organic in makeup. An example of simple nitrogen fertilizer would be one that lists only urea or ammonium sulfate as the ingredient. A simple phosphorus fertilizer might list superphosphate or ground mineral phosphate as the ingredient. A potassium fertilizer may list muriate of potash on the container.
Technically, all organic fertilizers are slow-release, as it takes time for organic matter to decompose in the presence of soil microorganisms. The slowest acting organic fertilizers include insoluble mineral fertilizers, like rock potash and other rock powders.
Gardeners who want to fertilize just once can shop for slow-release fertilizers that use coatings or capsule-like shells to control the release of the fertilizer for weeks or months. These types of fertilizers are especially popular with houseplant care.