Guide to Fertilizers

Behind any beautiful plant is great nutrition. Fertilizer is one of many components that contributes to healthy plant growth. With proper fertilizing your plants will have all the nutrients they need to put forth their biggest and most beautiful glossy, green leaves. But what is fertilizer anyway? What should you look for in a fertilizer and what does it provide for the plant? The core of any good fertilizer regiment starts with understanding the three core components of any fertilizer, the N-P-K ratios, denoted by a three number ratio on the bottle.

N-P-Okay!

The N-P-K ratio is the ratio of Nitrogen (N), Phosphorous (P), and Potassium (K) present in fertilizer, denoted by whole numbers representing the percentage the product contains by weight. For example, a 10-10-10 fertilizer contains 10% nitrogen by weight, 10% phosphorus by weight, and 10% potassium by weight; the remaining components of fertilizer are mostly inactive ingredients and fillers which aid in application and absorption. This number is important as it not only tells you the potency of a fertilizer, but also the ratio of nutrients it provides to the plants you fertilize. Variations in the ratio of N-P-K provide specialized nutrition for certain plant types or to produce certain outcomes, such as flowering or root development.

A Balanced Diet

A fertilizer that contains all three of these nutrients is considered a complete fertilizer, whereas fertilizers with one or more zeros in their N-P-K ratio are considered incomplete fertilizers, though they have their own value in specific applications, such as improving specific soil deficiencies in the garden. So why are nitrogen, phosphorus, and potassium singled out on fertilizer containers? These nutrients are required in the greatest quantities in plants as what are known as primary nutrients, or macronutrients, alongside Calcium, Magnesium, and Sulfur. These nutrients are essential for plant growth and affect specific aspects of plant growth and development.

• Nitrogen is a key nutrient in vegetative (non-flowering) plant growth, serving as a core component of amino acids involved in protein formation and plant growth. Nitrogen is also one of the main components of chlorophyll and is required for many vital plant enzyme reactions.
• Phosphorus is one of the main components in plant DNA and RNA, and is crucial in root development, plant maturation, flowering, fruit production, and seed production.
• Potassium, unlike Nitrogen and Phosphorus, is not a component of any specific plant part. Instead, potassium is required for activating over 80 enzymes throughout the plant, facilitating key functions including cold acclimation, drought tolerance, pest resistance, and more, and facilitates increased water consumption efficiency in plants.

Other nutrients which are required in much smaller quantities, though still quite important to plant functioning, are called micronutrients and are often present in fertilizers as well, though usually on the label itself rather than prominently on the front of the product. Plant micronutrients include Chlorine, Iron, Boron, Manganese, Zinc, Copper, Molybdenum, and Nickel.

When To Fertilize

Plants consume the greatest amount of nutrients when actively growing and producing new tissues. Therefore, the best time to fertilize a plant is while it is actively growing to supply plants with the nutrients they need and avoid stunted growth and nutrient deficiencies. The time and amount of fertilizer required will depend on the type of plant fertilized and the goal of the fertilization (vegetative growth, improved fruit production, etc.). Generally:

• Houseplants should be fertilized in Minnesota when we are entering our active growing season, providing greater light and warmer temperatures for your plants to help promote healthy new growth. Generally, houseplants should be fertilized from April through August. With the exception of grow lights, fertilization in the fall and winter can lead to plant stretching due to inadequate light levels. Additionally, many plants will enter a natural dormancy period during this time, including many succulents and cacti, and do not need additional nutrition.
• Annuals may be fertilized throughout the growing season, though it is not always necessary as they are often planted in nutrient rich mixes, providing needed nutrients throughout the season. However, bi-weekly or monthly fertilizing of annuals can promote more prolific blooming and vigorous growth.
• Perennials do not need all that much fertilizer to thrive. Perennials need to be fertilized at most twice per season, most importantly at the start of the growing season, around early May, and again at the peak of the season, around mid to late July. Overfertilizing of perennials can prevent blooming and cause nutrient burn in plants.

How to Fertilize

Like all good things in life, there is such a thing as too much. Overfertilization of plants can lead to a variety of issues including salt buildup in the soil, which will slowly deteriorate the health of your plants, as well as nutrient toxicity and even the growth of undesirable organisms such as algae in pots and beds. When it comes to fertilizing, less is definitely more; it is a good idea to test a new fertilizer or fertilizer on a new plant by applying at half the recommended rate to avoid toxicity and see how your plant responds to the product used. Fertilizing can also be used to help promote specific plant growth outcomes by the selection of certain N-P-K ratios. Fertilizers higher in Nitrogen will help bolster vegetative growth and green coloration, while fertilizers higher in Phosphorous and often Potassium will promote more prolific blooming and promote fruit, seed, and root production. Ensuring the correct N-P-K ratio, application rate, and timing will ensure your plants have everything they need to keep on growing strong.

Happy Planting!