There is no fertilizer, organic or otherwise, that contains the proper amounts of all macro- and micronutrients and alters the pH appropriately for every single plant type in existence. To achieve optimal results, it is best to design an organic fertilizer program based on your own unique soil characteristics and desired crops.
Before you begin, get a soil analysis. I cannot stress enough the importance of knowing your existing soil characteristics and attributes before amending it with anything. Once you know what your soil is lacking—or not—you can set out to create a blend of various amendments that will deliver the nutrients your hungry plants need.
Benefits of Soil Testing
An advanced degree in chemistry is not required to perform an effective soil test. You can do it yourself or have the soil analyzed by a lab. Most growers opt for an in-between scenario where you collect the sample, send it in and receive a profile of the soil type, pH, organic matter and the range of nutrient levels.
For the DIYer, most garden centers carry test kits that range from a few dollars to $50. Supply houses and online sources carry more sophisticated kits that can be obtained for a few hundred dollars. For the average gardener, a lab or local Extension Agency can perform this service as well, for a fee.
The most cost-effective method is usually to collect the samples yourself, following the directions of the lab, and then send them off to be professionally analyzed. This service is generally in the range of $15-30, and is the best bang for your buck. Collecting samples is easy. Make sure you have a clean trowel and a clean container.
Dig down in random spots of your garden to create a composite sample. Collecting soil from just one spot is not reliable, as there can be quite a range of nutrient and pH levels even in the same yard. Then send off the sample in a new, re-sealable bag or container provided by the lab.
Usually within a week’s time, you will have a near-complete picture of the conditions in your ground and will know where you have abundant nutrient levels and where nutrients are lacking. The benefit of having a lab analyze the test is that if you do not understand the results, they can help you interpret them and can also give you advice. This alone is usually worth the cost of the test.
Organic Vs. Synthetic Fertilizers
Once you know what minerals your garden needs, you need to choose what type of fertilizers to use in your garden. Synthetic fertilizers are man-made nutrients gleaned from a variety of materials, including petroleum. These fertilizers are generally uniform in particle size, spread easily and tend to be relatively inexpensive. They are also much higher in nutrients than organic fertilizers. While this may seem like you are getting a bargain, be wary. Your plants can only use so much of any given nutrient and any excess will go to waste or, worse, run off into the watershed, which has negative environmental repercussions.
Organic fertilizers are crafted from animal, mineral or plant sources and contain no artificial additives. They tend to be more expensive than synthetic fertilizers and have lower nutrient values, but this does not mean they are less effective. Organic fertilizers are not water-soluble like synthetic fertilizers, and they need to be broken down into plant-usable forms by soil micro-organisms first before they are of any use to plants, which means they take longer to work, but have much longer-lasting impacts on plants and soil. They can feed your plants for much longer than synthetic fertilizers.
Be careful with terms like organic, all-natural and the like, though. Materials that are mined or used in their original form may not be listed as organic, even when they are compatible with organic gardening regimes. The organic label is conferred to commercially prepared blends and products with more than one ingredient. Now, since this article is about organic fertilizer programs, we will examine how to provide plants with the nutrients they need in an organic program.
Read More: Combining Organic & Synthetic Nutrients
Organic Sources of Macronutrients
The nutrients your plants require in the largest amounts are the macronutrients: nitrogen (N), phosphorus (P), potassium (K) and, to a lesser extent, calcium (Ca), magnesium (Mg) and sulfur (S). Plants also need hydrogen (H), oxygen (O) and carbon (C), but these can be obtained from the environment. Many sources of organic macronutrients will contain micronutrients as well.
Common organic sources of nitrogen include corn gluten meal, cottonseed meal, soybean meal, bat guano, blood meal, feather meal and many of the fertilizers derived from fish and marine life such as fish emulsion. Organic phosphorus can be obtained from bat guano, bone meal and rock phosphate. Aside from corn gluten, blood meal and bone meal, all the previously mentioned sources contain some amount of organic potassium, which usually means no additional sources are necessary.
For calcium, magnesium and sulfur, mineral sources are often used, such as lime or magnesium sulphate. Lime will raise soil pH and sulfur will lower it, which will have to be taken into consideration based on your soil analysis results.
Organic Sources of Micronutrients
While no less important to the overall function of plants, micronutrients are needed in lower amounts than macronutrients. Many exist naturally in healthy soils or are added to many nutrient or additive products, but the ones of the most importance are chlorine, boron, iron, manganese, zinc, copper and molybdenum.
The full role of the other dozens of micronutrients is not fully understood, only that they are present in soils that support healthy plant growth. Most of these elements are vital for helping plants photosynthesize, set fruit and for heathy cellular division. Some ways to add a bunch of these important helpers to your garden include seaweed and kelp in powder, liquid or meal form.
Read Next: 8 Crop Micronutrients Growers Can't Ignore
Putting It All Together
Armed with the results of your soil test and the recommendations for your specific plants or crops, you can now go forth and proudly assemble the needed organic nutrients for your plants. Calculate how many pounds of each nutrient you will need based upon the square footage of the area you are working with, as most recommendations are in pounds of nutrient per acre, and the average home gardener grows plants and food on less than a quarter of an acre.
You can apply the nutrients one at a time, or create a blend. A clean wheelbarrow or even a 5-gal. bucket will suffice for this task. Just make sure you are not over-applying nutrients. While organic nutrients do not tend to leach or run off as much as their synthetic counterparts, there is no point in wasting money, time or materials by putting in more than your plants need.
You can create a dry blend or a liquid one. Liquid organic fertilizers can be applied in a pump-sprayer, added to irrigation water or even applied as a soil drench. Many organic powders and granules can be used to create liquid fertilizers. Most do not readily dissolve in water, but if left to steep, their respective minerals or nutrients will leach into the water and can be used in liquid applications.
Organic nutrients work slower than synthetic ones, so do not think that your efforts were in vain if you do not see immediate results. The good news is that organic nutrients stay in the soil longer, so they will be there when your plants need them.
Repeat the soil-testing process once per season to see how your soil is doing, as pH and nutrient levels fluctuate over time. By soil testing and amending as needed, you will ensure your plants have a comfortable home with plenty of good food for the entire growing season.