Plants need several inputs in order to survive and thrive. Water, of course, is essential, as it is for all living things; a medium in which to grow; and sunlight to enable them to photosynthesize are all key. But at a smaller scale, there are three elements that are essential ingredients to healthy plant growth: potassium, nitrogen and phosphorous. Each performs a different role for the plant, and making a good balance of these elements available to their plants is one of the roles of the permaculture gardener to ensure healthy plants and a good harvest. Fortunately there are methods and techniques that gardeners can employ to increase the presence of each of the three elements in the soil.
Nitrogen, taken up by plant roots from the soil after it has been processed into a soluble form by microorganisms, is essential for plants to develop proteins. These proteins are important for the development of cells within the plant. As such, nitrogen is needed for robust plant growth, speedy development of shoots, healthy flower bud development and a good quality harvest. It is also an essential chemical in the photosynthesis process, by which plants convert sunlight into useable energy. As such, you can tell if your soil is low in nitrogen if plant leaves turn yellowish and brown at the tips (however, be advised that because plants can move nitrogen around to benefit new growth, some old leaves will go yellow anyway, even if nitrogen is not deficient.).
If you are looking to increase the amount of nitrogen in the soil of your permaculture plot, there are several organic ways of doing so. Adding composted animal manure can help, and is easy if you have livestock. Poultry manure has high levels of nitrogen, but must be composted before application to the soil to prevent plant burn. Adding used coffee ground to compost is another method. If you want to increase the nitrogen content in a site prior to planting food crops, you could consider planting a ‘green manure’ crop. This is a cover crop, such as borage, clover or alfalfa that is grown then slashed and left to rot into the soil. When you have established your garden beds, adding nitrogen fixing plants is a good idea. These leguminous species, which include peas and beans, work with a bacteria commonly found in the soil to draw nitrogen from the air and store it in their roots. Some of this nitrogen penetrates into the soil and other plants can use it.
Phosphorus plays a number of important roles in the physical development of a plant. Firstly, it is used by the plant to move energy and nutrients around itself, so that all parts of the plant remain healthy. With nitrogen, it helps in the process of photosynthesis, while it also a crucial component in the formation of nucleic acids, which help form the plant’s DNA, and so helps plants grow strong and develop solid roots. An insufficient supply of phosphorous can cause leaves to wilt or die back, stems and veins on leaves to appear purple, and poor seed and fruit development.
Adding animal meal to the soil is one of the most effective ways to increase phosphorous levels. Fish or bone meal are both viable alternatives, though you should check the source of the meal to ensure that it does not come from animals that have been treated with antibiotics, and that it originates from a sustainable source. Animal manure, particularly from horses, can also help up phosphorus levels, as can adding rock phosphate, although this will take a longer time to break down. Be careful not to elevate phosphorus levels in the soil too much as excessive levels can adversely affect beneficial fungi in the soil, and even leach into groundwater.
Potassium is key to ensuring all the physiological process in a plant function normally. It is an element that helps the plant activate enzymes, form sugars, and synthesize proteins. Potassium exists in two forms in the soil, one soluble and the other not. Plants can only use the soluble form of potassium, as it functions within the stomata, the cell system within the plant that uses water to cycle nutrients around all parts of the plant. Good levels of potassium help the plant use moisture efficiently, which helps prevent disease and heat damage, as well as reducing the need for the plant to be irrigated. Too little potassium in the soil will lead to leaves curling and becoming distorted. Root systems are also unlikely to develop, particularly in young plants, while stalks can appear weak and spindly.
There are several ways that the permaculture gardener can increase the amount of potassium in the soil. The first solution, and the answer to lots of soil questions, is the addition of good compost. Lots of vegetable and fruit scraps – particularly banana – will provide a boost to the potassium levels in your compost, and the good thing about adding compost to the soil, is the potassium compounds within the compost are already in a water-soluble form, meaning plants can access them immediately. Adding wood ash – the remnants after burning hardwoods, to you compost is another method for increasing potassium levels, although it can affect the pH level of the soil, so test regularly. Kelp and granite dust are alternative methods (although the latter takes a relatively long time to release its nutrients).
There are other elements that are crucial to healthy plants, and which the permaculture gardener can ensure are available by maintaining a healthy soil. Calcium, for instance, helps build strong cell walls, magnesium is a central component in chlorophyll, the green pigment that is essential to photosynthesis, while sulfur is important in the formation of vitamins. However, nitrogen, phosphorous and potassium are the ‘big three’ – get the levels of those in the soil right, primarily by ensuring the soil has a lot of organic matter (which will have the knock-on effect of providing all the other elements needed by the plants) and you should be able to ensure a healthy garden and a bountiful harvest.