Plant nutrition is the key to healthy, productive plants
We've all heard it said that you are what you eat, and this same concept applies to plants! The cold, hard truth is that it's not only flavor that grocery store vegetables lack, the actual nutrition contained within them is lacking as well. These mass produced fruits and vegetables we have available to us year round in the supermarket have mostly been raised in sterile mediums and fed soluble fertilizers. While this system can produce an end product that looks nice and tastes decent, the nutrition contained within the food simply does not add up to what we can grow in our gardens. With this mindset as a foundation for how we want to raise our food, I will break down the basic nutrient requirements for plants and some of the common (and also more creative) ways of getting them everything they need to grow. Read on and never settle for a tomato that tastes like cardboard again!
The Macro-Nutrients
There are three main nutrients that all plants require for growth and these are known as macro-nutrients. For most commercially grown crops, these might be the only nutrients the plants receive their entire lives. Nitrogen, phosphorus, and potassium are found in every soluble fertilizer mix and cited on any bag of potting soil. Without adequate amounts of all three macro-nutrients, your plants will suffer and show visible symptoms of deficiency.
Nitrogen
Nitrogen deficiency commonly presents itself as yellowed, limp leaves and a general failure to thrive. Nitrogen gas is the most common element found in our atmosphere on earth. Unfortunately, nitrogen is not accessible to plants in its gas form. We need to provide our garden with soluble nitrogen in order for it to be absorbed through roots. Fortunately, there are tons of great resources for adding nitrogen to the soil! And as all good gardeners will tell you, feed the soil, not the plant. This translates into remembering that we do not actually need to provide our plants with soluble nitrogen, but rather add nitrogen rich materials in their original form and allow them to be processed naturally by healthy soil biota.
Compost is a great all-around fertilizer that includes nitrogen whether it was made using plant materials or animal manures (or a combination). This should be the first and foremost addition to your garden beds. Save your soil structure and don't till this in. Just add it on top and allow the worms, bacteria, etc. to incorporate it into the lower layers of your garden bed. The protective layer of compost acting as mulch will also help conserve the nutrients already stored in your soil.
Animal manures are probably the most potent way to add nitrogen to the garden. Some manures such as horse and chicken run "hot". They will burn the plants if applied directly to their roots. To prevent this, make sure these types of manure are composted first or applied in the fall and allowed to decompose some before planting. To prevent the potential spread of disease, these methods would be recommended for any type of animal manure.
Blood meal is a great nitrogen source and I use this in my potting mix. You can buy it in bags and you can even make it if you process your own animals. Sprinkling some on your garden each spring can be an easy way to feed your garden.
In the world of permaculture, the gardener is always attempting to achieve abundance and robust plant growth using methods that mimic the processes found in nature. By far the best way to achieve this effect is to use companion planting and crop rotation with plants that naturally convert nitrogen into its soluble form. Certain species such as those in the legume family have a symbiotic relationship with a nitrogen fixing bacteria that live in nodules on the root systems of these plants. These bacteria produce nitrogen in the soil that can then be accessed by the surrounding plants. Plants in the legume family include clover, peas, beans, vetch, lupines and more. To guarantee this positive effect of nitrogen conversion, the seeds must be inoculated with the specific bacteria before planting. In a very healthy soil, this bacteria will likely already be present, but if the soil has been previously damaged through poor agricultural or home gardening practices, it may be necessary to use the inoculation method. Pioneer tree species such as Red Buds and Black Locusts are nitrogen fixing species which are commonly found in disturbed sites where recolonization of forests are occurring. They are some of the first species to arrive and begin the process of soil repair to create a more hospitable habitat for other late succession forest species. Because of this, these types of trees should be included in food forests and permaculture orchards to provide a stable source of nitrogen to the surrounding plant species.
One last way of providing nitrogen to the soil is so surprising and unusual that I just have to include it here. Lightning and the static caused by thunderstorms can actually sink nitrogen into the ground. Some farmers have been known to place metal poles throughout their fields to collect and deposit this static electricity into the ground!
With all of these different techniques for adding nitrogen to the soil, gardeners have plenty of options that will work for them without using any kind of store-bought fertilizers.
Phosphorus
Phosphorus is the second of the three macro-nutrients. This element is typically obtained through mined rock which modern humanity is having no difficulty using up at an alarming rate. This rock is ground up into powder or a small particle size and mixed into a soluble format which is sprayed in mass quantities on our farm fields to feed the crops. When the quantity of phosphorus rock available starts to dwindle and the prices get higher and higher on this material, the standard food system as we know it will be facing some serious challenges. Known as "peak phosphorus", this effect is one that we should be mindful of and take preventative steps against. By using regenerative gardening practices, we can build complete resilience against the inevitable unavailability of mined phosphorus and reduce our overall negative impact on the planet.
"By using regenerative practices, we can build complete resilience against the inevitable unavailability of mined phosphorus"
Rock phosphate and colloidal phosphate are two mined sources of phosphorus readily bought in bags from garden centers. While I do use rock phosphate currently in my soil mixes, I do not add this to my garden beds. There are plenty of natural and readily available sources of phosphorus that can be used to supply this nutrient! Animal manures and compost are great sources of phosphorus. Both of these fertilizers should be used regularly for their all-around greatness at building healthy soil. I like to spread a nice thick layer of homemade compost on my annual garden beds each fall to protect the soil over the winter and provide nutrition for the growing season.
Bone meal is another strong source of phosphorus. Because it is made from animal bones which are a renewable resource, it can be considered a more environmentally conscious option. Bags bought in the store are likely made of commercially raised cattle bones, but you could certainly make it yourself if you process your own animals. Just dry the bones and grind them into a powder. Even whole bones are a source of fertilizer over time as they break down. Have I been known to bury chicken bones in my garden?... yes. Do I bury the bones, scales and guts of the fish we occasionally catch and eat?... yes. Any animal byproducts can be great fertilizers given that you understand the risks of attracting wild animals that may dig up your garden. I do speak from personal experience! Fences, deep enough holes and flat rocks placed on top can prevent the animals from finding your bones if you choose to do this!
Potassium
Lovingly abbreviated with a "K" in chemistry and on fertilizer ingredient lists, potassium is actually one of the most common elements found on earth. Rather than attempting to add this nutrient to your soil, gardeners should think more in terms of how they will help their plants access the potassium that is already there. Some prominent organic farmers such as Eliot Coleman use a subsoiler occasionally to dig up the lower, mineral layers of soil and raise them into the upper layers where annual plant roots are found. This is effective although it won't work with no-dig gardens.
Chop and drop methods are another great way of making the local potassium supply accessible. Grow deep-rooted plants near shallow-rooted ones and mulch your beds with the deep-rooted plant's leaves. Burdock, comfrey, dandelion, rhubarb and so many other low growing perennials can be great choices. Just cut the leaves and lay them at the base of your other plants. This classic permaculture method is directly imitating the processes found in nature. As the leaves are broken down, they will supply all different minerals right into the top layers of the soil.
Many aquatic sourced fertilizers can help supply potassium. Kelp meal, greensand and algae can all be obtained from the ocean and are renewable options for adding potassium. Wood ashes are one of my favorite potassium fertilizers to use. Make sure you are only burning natural wood; hardwoods are best. Not only are the ashes fertilizer themselves, they can help raise the pH of the soil. Most plants prefer growing in neutral soils and their ability to absorb nutrients will increase when the pH is correct.
The Micro-Nutrients
There is an abundance of micro-nutrients that are regularly forgotten to consider unless a deficiency becomes evident. Iron, calcium, magnesium, sulfur, boron and zinc are some to name a few. Generous additions of compost yearly will supply many of these naturally. Chop and drop is an ideal way to make sure that your garden is receiving a well-rounded source of micro-nutrients. Certain plants such as comfrey are known as dynamic accumulators. These plants are excellent at absorbing all sorts of nutrients from the soil that are difficult for other plants to access. When you cut the leaves of these plants and mulch your garden beds with them, nutrients contained within the leaves become available through the decomposition process.
Adequate water and the proper pH will greatly increase the absorption ability of your plants. For example, blossom end rot on tomatoes is caused by a calcium deficiency. The common reason for this deficiency is actually not usually a lack of calcium in the soil, but rather insufficient water which prevents the tomatoes from absorbing the calcium. Good soil management and plant care practices will take care of 90% of the micro-nutrient needs in your garden. If a deficiency becomes obvious, there are more direct ways of correcting the problem. For instance, Epsom salts can add calcium and borax can add boron. Always take care when using such refined forms of a mineral because too much can cause issues that are irreversible without physically removing the affected soil and replacing it.
Conclusion
Hopefully this information is helpful and liberating! Soil nutrition does not have to come from expensive bags of fertilizer. Most everyone has at least several free and abundant sources of plant food on their own property! With this knowledge and intentional design, the home gardener can create a system that is in no way reliant on outside sources for growing healthy and nutritious plants right out of their yard. If you don't already have one, build a compost pile, plant some dynamic accumulators and get creative! It won't be long before you have the best looking (and tasting) plants on the block!