You’ve seen the three numbers on fertilizers. This is called the chemical analysis or fertilizer analysis. Those numbers (and their chemical symbols) are, in order, nitrogen (N), phosphorus (P), and potassium (K). Gardeners often refer to potassium as “potash”. (Potash reminds me of a funny story which I will tack onto the end of this blog post.) The numbers represent the percentage of the product that is composed of each chemical. The numbers won’t add up to 100%. The remainder of the product is filler, including inert components that will aid in dispersing the chemicals.
You know I prefer organic fertilizers and pesticides. So I will give you a list of good organic sources of these chemicals needed by all plants.
Nitrogen promotes lush green lawns, and beautiful leaves with strong stems. All plants need some nitrogen, but needs vary. Look to high-nitrogen fertilizers for turf grasses and foliage plants such as this fern.
The Best Sources of Nitrogen
- Composted Cow Manure — should be at least 6 months old.
- Composted Chicken Manure — should be at least 4 months old.
- Blood Meal — in order not to burn plants, dissolve in water before applying to plants, or work into soil before planting.
- Fish Emulsion — this can be very stinky, but is an excellent organic fertilizer. It can be diluted with water to weaken the odor.
- Coffee grounds — used coffee grounds are only about 2% nitrogen, yet they are a great soil amendment.
Phosphorous promotes strong, healthy roots and generates lush flowers and fruit production. If it’s lots of flowers, tomatoes, and other fruits that you want, look for a fertilizer that is high in phosphorous, i.e., look for a high middle number.
The Best Sources of Phosphorous
- Bone Meal — a great slow-release form of phosphorous and calcium, and my personal favorite.
- Banana Peels
- Crab and Shrimp shells — be aware the odor may offend your neighbors, and may attract critters to your compost bin. You can dry them, then grind them in a coffee grinder used only for this purpose and for grinding eggshells.
- Bat Guano — can be purchased.
- Fish Bone Meal — can be purchased.
Potassium works on the inside of the plant, building strong cells and healthy tissues. This enables plants to withstand common plant stressors: diseases, pests, even heat and cold. All plants need potassium, but some need more than others. When shopping for plant foods, you will notice that those intended for winterizing lawns will have a higher number for potassium.
The Best Sources of Potassium
- Granite Dust (or Meal) — this is finely ground granite that is a great slow-release source of potassium. It also serves to maintain good soil drainage and to create good soil structure.
- Eggshells — Eggshells are primarily made of calcium carbonate, but they also contain potassium.
- Ashes of Hardwoods from Your Fireplace — while hardwood ashes are an excellent source of potash, they will also raise the pH levels of your soil, so be sure to keep a check on your soil’s pH levels. These days, you can buy a soil test kit at any garden center.
- Kelp (Seaweed) Meal — this can be in a dried and powered or liquid form. Both forms are fairly quick-release. Kelp meal can be purchased from many garden centers. If you live by the ocean, and can collect your own, lucky you.
Choosing the Right Fertilizer for Your Needs
Before spending money on fertilizers, think about which plants you will be using it on, and the specific needs of those plants. By choosing the individual organic compounds, you can target the needs of your plants much more accurately. I prefer this method over those large bags of (often synthetic) chemical fertilizers that may be good for one plant, but not so good for another.
The Funny Story I Promised
One of my uncles sent off a soil sample to one of the labs at Auburn University that will do these tests for you, for a fee, of course. When he received the results, he decided that he needed to be sure “those students” knew what they were doing, so he sent another sample. He intentionally added a large amount of ashes from his fireplace to the second sample. In about two weeks he received a brief note along with the soil analysis. Among other things, the note said, in bold print, “No more potash!” He then announced, “Those kids know what they’re doing down there.”