Plants need nutrients to grow. Good soil provides 14 essential plant nutrients for plants to utilize. These nutrients are classified as primary, secondary and micronutrients. The primary nutrients are nitrogen, phosphorus and potassium and the most common nutrient deficiencies are a lack of one of these three elements, which are labeled as NPK on fertilizer products as percentage of each nutrient in the mixture. For example, a product labeled 20-16-20 has 20% nitrogen, 16% phosphorus, and 20% potassium. Plants need more of these primary nutrients over the secondary and micronutrients to grow. Nitrogen is utilized by plants for almost all aspects of plant growth from plant hormones to DNA to chlorophyll and by amount is the most needed element of all the nutrients. So, how do plants get this critical element? The nitrogen cycle is how this is accomplished.

The nitrogen cycle is how mother nature provides this critical element for plant growth and ultimately oxygen production that we benefit from. Nitrogen is available from two sources, atmospheric nitrogen and organic nitrogen. Nitrogen makes up approximately 78% of the air we breathe with the rest being oxygen and small amounts of trace gases. Organic nitrogen is found in soil primarily from decomposing plant residue and animal manure/biosolids. These forms of nitrogen are not available to plants and must be converted to NH4+ (ammonia) and NO3- (nitrates) that plants can use. This is where the nitrogen cycle starts. Two processes make this conversion happen, nitrogen fixation and mineralization. Nitrogen fixation is the process of converting atmospheric nitrogen into useable nitrogen and mineralization converts organic nitrogen compounds into useable nitrogen. Soil microbes and fungi are responsible for doing this critical conversion and as soil temperatures rise this process proceeds at a faster rate. Did you know that about 1/4 teaspoon of soil can contain up to one billion microorganisms? Legumes form a symbiotic relationship with nitrogen fixing bacteria at the root. The plant provides nutrients to the bacteria which form nodules in the root to take in atmospheric nitrogen in the soil and convert it to ammonia which is then used by the plant. Examples of legumes are beans, peas, lentils, and clover. After the plant uptakes the usable nitrogen for DNA, proteins, or whatever else the plant needs, and ends its life cycle, the mineralization process starts again with bacterial and fungal decomposers.

The nitrogen cycle is not 100% efficient. Nitrogen is removed from the cycle by denitrification and leaching. Unused ammonia is rapidly converted to nitrates which are useable to plants but also useable by denitrifying bacteria. These bacteria convert nitrates back to free atmospheric nitrogen. Since nitrates have a negative charge, it is not held by organic matter or clay and is very soluble in water so excess nitrate runs off and leaches into ground water, streams, and lakes. This is why it is a good practice to not over fertilize. Harvesting crops also removes nitrogen but composting your harvested plants and leaving the roots in the soil after harvest helps to reduce the need for additional fertilizer.

A good fertilization program is an important part of gardening. Most of the time additional nutrients need to be added. Most of us intuitively know that planting year after year in the same area depletes the soil nutrients. We also know that certain plants have different nutritional requirements. Soil testing can give you the exact amount of fertilizer to use. Soil tests can be purchased through online retailers where you send in a soil sample and they will send you a detailed result. Commercial labs will also perform soil testing. Refer to WSU publication by clicking on the following link: EB1578E Analytical Laboratories and Consultants Serving Agriculture in the Pacific Northwest. The result will tell you what is currently in your soil, the soil pH, and recommendations on what elements and the quantity needed to augment your soil for best results. These tests cost around thirty dollars per test. Home tests that you can do yourself are also available in many stores that sell garden supplies. They are not as detailed as a soil send out test but are less expensive and can give you a starting point for nitrogen, phosphate, and potassium, along with pH. Battery powered probes that can read pH are also available. Soil tests can be done every 3-4 years with rotation of crops and are probably not needed in established landscape beds. Crop rotation from heavy feeding plants (ex. berries, tomatoes, cabbage, corn, squash) to light feeding/intermediate feeding plants (beans, peas, carrots, lettuce, spinach) will decrease the amount of supplemental fertilizer you will need.

Fertilizers come in a multitude of forms and proportions. The correct one can be found for most any situation. They are available in inorganic or organic forms. Inorganic fertilizer is made from chemicals and minerals and does not contain carbon while organic fertilizer is made from natural carbon-based sources (plants, animals, and manure). Generally inorganic forms work more quickly unless labeled as slow release and organic forms release nutrients more slowly. Gardeners at Garden by the Sea practice organic gardening and use organic products to use in our gardens. Fertilizer should be applied according to the package labeling and in a conservative manner. Make your buying decision based on what you need, the cost, and your personal gardening preferences and priorities. Now would be a great time for a soil test so you can set yourself up for success when planning what to plant while waiting for spring to get here.

For further information, please feel free to email us at info@GardenByTheSeaOceanShores.org