Nitrogen, phosphorus and potassium are the key garden macronutrients. One is

As many know, healthy, nutrient-rich soil supports a productive vegetable garden. Nitrogen (N), phosphorus (P), and potassium (K) are the key macronutrients required by plants for their growth. When you see a fertilizer bag with numbers on it, stating something along the lines of 13-13-13, 46-0-0, 10-5-14, etc., these numbers directly correlate to the amount of N, P, and K, respectively, you can find in the bag.

But what about organic gardening? Many vegetable gardeners are understandably not fans of putting chemicals near their food. What sources are available to provide these nutrients naturally?

Nitrogen is the key macro-nutrient that will always need re-supplementation in the soil. Plants actively deplete this nutrient during the growing season as they produce chlorophyll and photosynthesize, ultimately feeding the plants. While the plants also use phosphorous (for growth) and potassium (for water pressure), they are typically used in much smaller amounts. Therefore, if a soil area has been recently supplemented within the last few growing seasons, it will likely still have plenty of phosphorus and potassium available. This makes finding sources of nitrogen the top priority when considering organic fertilization, and it can be slightly more difficult than meets the eye..

While compost is an excellent soil additive for incorporating humus, which ultimately increases carbon-nitrogen exchange (and feeds plants), it doesn’t usually supply more N, P and K to the soil. Composted manure, however, can be an excellent nitrogen source, provided it is incorporated in the fall and given time to work into the soil. As mentioned, though, nitrogen needs to be replenished through the growing season because it is so actively used by plants, which makes compost ill-timed when it should only be added in the fall.

Blood meal (12-0-0) at a rate of 5 to 10 pounds per 100 square feet, cottonseed meal (6-0-1) at 10 pounds per 100 square feet, and soybean meal (7-2-1) at 8 pounds per 100 square feet are all decent organic sources of nitrogen. Elsewhere, bat guano, bone meal, crab waste, burned cucumber skins, hair, mushroom compost, phosphate and shrimp waste can all be good sources of phosphorous. Granite dust, greensand, kaolinite clay, kelp and wood ashes can all be decent sources of potassium.

As with any fertilizer, organically resourced or not, application of the product should ultimately be done following label instructions to protect your health, that of othersa nd that of the environment.

It is also essential to remember while handling these products, some may have adverse effects that are very much undesirable. Depending on the source, bat guano can hold many pathogens that are dangerous to human health. Wood ashes, from a horticultural perspective, will spike the pH of non-acidic soil into unhealthy levels for plants.

While the desired nutrients may be present in these, other side effects of the sources should be thoroughly researched before investment and application. Organic sources can also be slow and unpredictable, so patience is critical.

Anthony Reardon is a horticulture agent with Kansas State University Research and Extension. The K-State Johnson County Extension office can help facilitate analysis of where your soil is for specific nutrient analysis when we send your soil sample to the K-State soil lab. More detailed information can be found on our website, our Garden Hotline at 913-715-7050, or by email at garden.help@jocogov.org.