How to Fertilize Your Plants: All About Nitrogen, the ’N’ in ’N-P-K’

NPK Fertilizer Explanation gardeningNitrogen exists in all living cells. It is the protein builder in plants, and a vital part of the chlorophyll molecule because it is necessary for photosynthesis to occur. Nitrogen basically allows cell formation to take place, and is the building block behind vegetative growth. Nitrogen is found in plant and animal waste in the form of organic matter. Your aged compost is rich with nitrogen.

Signs of a Lack of Nitrogen

If there is a lack of nitrogen in your soil, you will notice plants may have stunted growth, yellowing leaves, or smaller than normal leaf size. Eventually, nitrogen deficient plants will drop their leaves prematurely during the growing season.

Sources of Nitrogen

The best source of nitrogen is organic matter. Compost and manure contain a relatively low amount of nitrogen, and if properly aged can provide plants with available forms of nitrogen that won’t burn roots. Industrial sources of nitrogen, or synthetic fertilizers, are also derived from processed animal waste. They can be formulated to provide a source of fast or slow fertilizers, and create consistent results.
On the other hand, too much nitrogen can cause soft, lush growth without any structural rigidity. This type of plant growth tends to attract pests such as aphids. Foliage may also go excessively dark.

So how did you end up with depleted soil?

Nitrogen is leached from soil by water, rain or irrigation. Soil naturally loses minerals over time. And the removal of green tissue such as debris and clippings reduces the breakdown of new nitrogen from gardens and lawns. In really wet soils where there is a lack of oxygen, anaerobic processes take over and can reduce the amount of nitrogen available to plants.

How Much Fertilizer or Compost Should I Use?

Too much nitrogen is not a good thing for plants, as it typically ends up attracting pests that will eat your lush new growth. Excessive nitrogen is not good for the environment either. Nitrogen that leaches out of your garden beds and ends up in water sources is responsible for increased algae growth in water bodies. Excess algae reduces oxygen levels in water which in turn suffocates fish and plant life.
The top techniques for using nitrogen fertilizer is to choose fertilizers with low levels of nitrogen. Make multiple small applications instead a few large ones. Time your applications with plant growth cycles. And test your soil to determine if there is already available Nitrogen, and whether you need to apply any at all.
In my years spent gardening, we have always removed all of the clippings and debris from garden beds for aesthetic reasons. Our customers want a super tidy estate-like look for their yards. Every year or two, as necessary, we always top dressed all garden beds with a two to three inch layer of composted bark mulch. We called this the best money anyone could spend in their garden. Thanks to this rich layer of shredded bark and green waste that had been composted for a period of time, we rarely had to use chemical fertilizers on our customer’s gardens. The bark mulch also reduced watering needs, prevents weed seeds from growing, provided a protective layer and looked really nice. We weren’t kidding about the good value! This same type of application of a good quality garden soil mixed with sand, applied to lawns, provides an organic source of nutrients and the results are beautiful.

Setting Your Garden Up For Success

Gardens do require the right set of conditions in order for any available nitrogen to be easily absorbed. Maintaining a soil pH of 7.5-8, keeping soil averagely moist (not saturated), keeping soil aerated by leaving in structural elements such as sticks and soil clumps to create air pockets, and continually adding composted plant waste help to ensure that the right kind of chemistry is going on in order for nitrogen to become available and to actually get absorbed by plants.

Other interesting ways nitrogen becomes available to plants.

Thunder and lightning storms release atmospheric nitrogen. During an electrical storm, the heat combines with nitrogen in the atmosphere and makes it available to plants. Bacteria in the soil are also able to fixate nitrogen found in the atmosphere by converting nitrogen to nitrate immediately into the soil.
Legume crops such as white clover or alfalfa have the ability to fix atmospheric nitrogen into the plant system. Plants from the pea and bean families are often used to revitalize farm lands where the nitrogen has been depleted from the soil. Legumes are used as an important part of crop rotation because of their ability to remediate depleted soils with new nitrogen molecules. You may have seen alfalfa used as a “cover crop” for this very reason.
When applying nitrogen, it is important to only use the amount that is actually needed by the plant. The less chemical fertilizers used, the better. Carefully managing the factors that influence a plant’s ability to absorb nutrients, as outlined above, will benefit both plants and the planet the planet in the long run.