Overview of Fertilizers for Outdoor Plants
What is fertilizer?
A chemical or natural substance added to soil or land to increase its fertility.
Why do we use fertilizers?
To help improve or maintain a plant’s health.
To encourage a plant to grow or produce fruit or flowers
What do the letters and numbers mean?
Fertilizer labels have three letters N P K which stand for Nitrogen. Phosphorus and Potassium respectively.
These are considered the macronutrients plants need.
- Nitrogen helps produce green foliage and stems and general growth
- Phosphorus helps develop roots as well flowers and fruit
- Potassium helps protect plants from stress and disease
The numbers are percentages of the total volume each chemical makes up. For instance 16-4-8 means 16% of the volume is nitrogen, 4% is phosphorus and 8% is potassium. The remainder is made up of micronutrients and fillers.
Micronutrients are essential plant nutrients that are found in trace amounts in tissue, but play an important role in a plants’ growth and development. There are seven micronutrients that combined often make up less than 1% of a plant, but if one or more or lacking it can really affect a plants health.
Organic vs Synthetic
Organic fertilizers are derived from natural plant or animal materials as well as mined rock materials.
Synthetic fertilizers are chemically produced to provide specific amounts of nutrients. Their rate of release can also be manipulated to act faster or slower.
Pros & Cons of organic fertilizer
Pros
- Environmentally sound
- Slow release providing nutrients for a longer period of time, and also ensuring the total amount of a given nutrient will be available for your plants over time
- Used repeatedly organic fertilizers often improve the makeup of the soil making it a more sustainable environment.
Cons
- Since they are slow release they do not provide a quick fix to remedy a problem
- More expensive than synthetics
- Usually not available in high percentages so more fertilizer is needed compared to synthetics
Pros & Cons of synthetic fertilizer
Pros
- Can purchase with higher rates of nutrients and designed for specific purposes.
- Release times can be more controlled with chemical and coatings though these can vary with frequencies of rain and irrigation
- Can be used for quick fixes if remedying a problem
- Less expensive to purchase
Cons
- Can be environmentally unsound as they add toxins and salts to the soil and water systems
- Don’t always get the amounts of nutrients advertised as the chemicals can become volatile over time and can dissipate quickly with frequent rains and often used irrigations systems
Granular vs Liquid or Water Soluble Fertilizers
Granular fertilizers are longer lasting allowing more time for a plant to take up the needed nutrients. When your plants or grass is healthy you may want to use granular. Granular fertilizers are often cheaper.
Liquid fertilizers are fast acting if you need to solve a problem, but also have a very limited time to work thus needing more frequent applications.
Can you do both? Yes slow acting granular fertilizers can be supplemented with liquid fertilizer in between applications.
Best times to apply fertilizers
Armed with some knowledge you can better determine the best time to apply fertilizers based on your plants and their needs.
Most plants and grasses start emerging form dormancy in March or early April. That’s when they start taking up more moisture and nutrients, so it makes sense to have the majority of the fertilizer you are applying available then.
To help maintain healthy plants and lawns reapplying fertilizer throughout the growing season makes sense. Late in the season before plants go into dormancy is another time to apply fertilizers so plants are armed with the nutrients to stay healthy over the winter.
When plants are suffering from malnutrition then that is the time to use a fast acting fertilizer or help get the situation under control.
Long-blooming annuals, perennials and roses as well as fruit bearing plants need a steady stream of nutrients to put energy into flowering or producing fruit.
