Healthy soil is the basis of organic gardening, and compost, or humus, is the basis of healthy soil.
Good humus-y soil has a structure that retains water, air, and nutrients, and allows for drainage. It provides food and habitat for worms, insects, fungi, bacteria, and burrowing mammals, all of which further improve the soil with their daily activity.
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The Perfect Soil
In a perfect world, your soil always has the proper balance of macronutrients nitrogen, phosphorus, and potassium (NPK); secondary nutrients calcium, magnesium, and sulfur; and a half dozen micronutrients. Plants pull these out of the soil each season, and rain and irrigation can leach them out. If you replenish your gardens with compost each year, you can naturally build them back up.
What is Fertilizer?
Sometimes, though, you will need or want to add fertilizer. ‘Fertilizer’ is a pretty broad term. It encompasses slow release amendments, water-soluble applications for quick fixes, and cover cropping or green manure. Before you take action, though, do a soil test.
Test Your Soil
Contact your County Extension to get a soil testing kit. You will collect soil samples from various parts of your garden, and send them to a lab stating the crops you want to grow. The lab will send you information and recommendations about adjusting the pH and adding nutrients.
Proper pH is crucial, because certain nutrients will not be available for plant uptake if the pH is too high or too low. No matter how much fertilizer or compost you add, the wrong pH will keep it from feeding the plants. You may have to adjust the pH, then do another test before applying amendments. Here is more on pH and an excellent chart showing the relationship between it and nutrient availability.
You will also receive recommendations for macro- and micronutrients, and it’s safe to assume they are not organic. This page from Harvest to Table gives you a list of organic alternatives to use instead. These are mostly slow release amendments that are good to put down in late fall or early spring. They will break down and be available in time for planting. It doesn’t hurt to do another soil test in the spring to be sure you have the proper nutrients for your crops.
Water-soluble fertilizers are the type you use to feed your houseplants or container plantings. They are granular that you till into the soil, or concentrates that you dilute and apply to the foliage or soil. These are good maintenance fertilizers to use while you are waiting for the slow release amendments to break down, or if your plants need a boost during the season.
These fertilizers offer a quick fix. Go to a reputable nursery or garden center, tell them what’s wrong in the garden, and they will point you to the right product. Be sure to tell them you want organic fertilizer. There are dozens of organic brands on the market today.
Cover crops and organic matter are other long-term, slow release fertilizers that also help build up healthy soil. Organic matter includes compost and natural mulches (straw, grass clippings, shredded leaves) that break down in the garden and release nutrients available to the plants.
Cover crops, also known as green manure, have many uses besides adding nutrients to the soil. They improve soil structure, smother weeds, and reduce erosion. Plant cover crops in fall for the winter, or in new beds any time during the growing season. As they grow, the roots break up the soil to aerate it. When the new growth is fresh and green, till it into the soil for the most efficient release of macronutrients.
Adding organic matter is good for the soil, whereas water-soluble fertilizers only add nutrients. Use both for best yields.
How to Make Organic Fertilizer
To mix your own fertilizer, you will first need to know what kind of soil you have. Sand, loam, and clay hold onto nutrients differently. Talk to your County Extension agent about soil types.
Again, you will need a soil test to determine pH and nutrient deficiencies and needs. You will also need to fully understand macro- and micronutrients, and you will need to source them. I personally think making your own fertilizer can be risky, especially if you’re not an experienced gardener. It’s too easy to ruin a crop with an excess of any element.
But if you are adventurous and want to experiment, here is an overview of organic fertilizers and a recipe for a basic, all-around mix.
In the end, though, the best organic fertilizer is the constant application of compost. And you can make that!