Searching for the perfect fertilizer for trees and shrubs to thrive can be confusing when faced with different numbers on containers like 10-15-10 or 10-5-4. Maybe it’s safer to go with the bag made for specific trees such as palms, but then you wonder if it would harm the crape myrtle in the middle of the planting bed. The good news is once you have the basics down, the numbers make sense and you can concentrate on the optimal fertilizing practices that keep your Tallahassee trees and shrubs thriving.
What the Fertilizer Numbers Mean
The numbers on fertilizer represent the fertilizer’s N-P-K ratio, which stands for nitrogen, phosphorus, and potassium. These are the three primary nutrients that plants need to grow, and the numbers represent the percentage of each nutrient in the fertilizer.
For example, a bag of fertilizer labeled 10-10-10 contains 10% nitrogen (N), 10% phosphorus (P), and 10% potassium (K) by weight. The remaining 70% of the fertilizer may consist of other nutrients or additives.
Different trees and shrubs have different nutrient requirements, so it’s important to choose a fertilizer with the appropriate N-P-K ratio. Generally, producing fruit or flowers requires a higher phosphorus content, while foliage-focused growth benefits from a higher nitrogen content. Potassium is important for overall health, helping trees and shrubs resist disease and stress.
Fertilizers can be organic or inorganic, and may also contain other ingredients, such as beneficial microorganisms, growth stimulants or soil conditioners.
Other Ingredients in Fertilizers for Trees and Shrubs
Specific nutrient needs can vary depending on factors such as the species, age and growing conditions. In addition to nitrogen, phosphorus and potassium, other key nutrients to consider for tree and shrub health include:
- Calcium (Ca) – Calcium helps maintain cell wall integrity and promotes overall plant health. It also plays a role in regulating soil pH and nutrient availability.
- Magnesium (Mg) – Magnesium is essential for photosynthesis, enzyme activation and other metabolic processes. It is often deficient in soils with high potassium levels.
- Iron (Fe), Zinc (Zn), and other micronutrients – Trees also require various micronutrients in smaller quantities for proper growth and development. Iron is important for chlorophyll production, while zinc plays a role in enzyme activation and hormone synthesis.
There are additional nutrients and additives in most commercially produced fertilizers that help in soil health and absorption. Be sure to ask your arborist when you have a question about specific needs for the trees in your landscape.
Concentrated vs Slow-Release vs Water Soluble
Not all fertilizers for trees and shrubs are meant to be applied in the same way. Concentrated, slow-release and water-soluble fertilizers differ in their formulation, nutrient content and release rate. Here are some of the key differences:
Concentrated fertilizers are generally high in nutrient content and are intended to be applied in smaller quantities than other types of fertilizers. They typically come in liquid or powder form and are applied to the soil or foliage. Concentrated fertilizers provide a quick source of nutrients, but need to be reapplied frequently to maintain nutrient levels.
Slow-release fertilizers are designed to provide a steady, long-term supply of nutrients to plants. They typically come in granular or pellet form and are applied to the soil. Slow-release fertilizers are coated with a material that breaks down over time, releasing nutrients gradually. This helps to avoid over-fertilization and can result in more even growth and better plant health.
Water-soluble fertilizers are mixed with water and applied to the soil or foliage. They are quickly absorbed by plants and provide a rapid source of nutrients. Water-soluble fertilizers are often used for foliar feeding, which involves applying fertilizer directly to the leaves. They can also be used as a supplement to other fertilizers.
In general, concentrated fertilizers are best for providing a quick boost, while slow-release fertilizers are ideal for providing a steady, long-term supply of nutrients. Water-soluble fertilizers are useful for quick, targeted applications, such as foliar feeding. The choice of fertilizer will depend on the specific needs of the trees and shrubs being grown.
Organic Fertilizer Alternatives
Organic fertilizers are derived from natural sources, such as plants, animals and minerals. They provide a variety of nutrients and can help improve soil health. Here are some common organic fertilizer solutions:
Compost is made from decomposed organic matter, such as food scraps, yard waste and manure. It is a rich source of nutrients, including nitrogen, phosphorus and potassium, as well as beneficial microorganisms that help improve soil health. Compost can be added to soil as an amendment or used as a top dressing around plants.
Animal manure, such as cow, horse or chicken manure is also a rich source of nitrogen, phosphorus and potassium. It can be added to soil as a soil amendment or used as a top dressing around plants.
NOTE: Manure should be aged or composted before use to avoid burning plants with high levels of nitrogen. Fresh manure can be acidic and may lower the pH of soil, making it difficult for plants to absorb nutrients.
Fish emulsion is a sustainable and environmentally friendly fertilizer option that utilizes waste materials from the fish processing industry. It is made from ground-up fish and is a rich source of nitrogen, phosphorus and potassium. It can be used as a liquid fertilizer for plants or as a foliar spray.
NOTE: While it is possible to make this a DIY project, it entails grinding, fermenting and straining of fish scraps and byproducts. It is probably best to purchase at a retailer – commercially sold emulsion has gone through a pasteurization process that makes it more stable. The smell is considered unpleasant by most but can be minimized by application being done on a calm day with minimal wind and away from open windows or intake vents.
In addition to the fertilizers and nutrients mentioned, trees and shrubs require adequate water, sunlight and carbon dioxide to grow and thrive. Removing dead branches and proper pruning will keep your trees and shrubs strong, with proper air movement reducing wind damage and diseases.
Best Practices for the Environment
Fertilizers for trees and shrubs are most effective when in the correct combination of nutrients, in the right quantity and applied at the best time of year. Adhering to application instructions also protects your plants from chemical burn and minimizes impact on water and soil balances.
Here is a list of fertilizer best practices for easy reference:
Test your soil: Before applying any fertilizer, it is important to know the nutrient needs of your soil. Understanding which nutrients are lacking and which are abundant will help you choose the right fertilizer and avoid over-fertilization.
Follow the instructions: Always follow the instructions on the fertilizer label. Over-fertilization can lead to nutrient imbalances, pollution of waterways and damage to plants.
Apply at the right time: Apply the fertilizer for your trees and shrubs when they are actively growing and in need of nutrients. Avoid applying fertilizer during times of drought or high heat, as this can damage plants and increase the risk of nutrient runoff.
Apply at the right rate: Apply fertilizer at the recommended rate for your soil and tree or shrub. Using too much fertilizer can lead to nutrient leaching and runoff, while using too little can lead to stunted growth and poor plant health.
Apply evenly: Spread fertilizer evenly over the soil or apply it uniformly to foliage. Uneven application can lead to over-fertilization in some areas and under-fertilization in others.
Store and dispose of fertilizers properly: Keep fertilizers in a dry, cool place – away from children and pets. Dispose of unused fertilizer properly, following local regulations.
At Miller’s Tree Service, we help our clients with the care of their trees, shrubs and landscaping. Our certified arborists can answer your questions about nutrients while assessing the trimming or removal needs of your trees. Call 850.894.TREE (8733) to schedule a free arborist consultation – we are invested in keeping Tallahassee trees and shrubs looking their best!