Last Updated on March 18, 2022 by Zachary Smith
Trees and shrubs are living things. Just like us, they need nutrients, water, light, and air.
Tree nutrition, however, is something many people struggle with. They wonder how they should be fertilizing their trees, how often, and which fertilizer blend to use.
The confusion is understandable – fertilizer is widely misunderstood. People wonder how to fertilize trees.
They tend to apply too much fertilizer, too little, or the wrong type at the wrong time of year. The results of that approach are varied.
At worst, the tree dies. At best, it fails to thrive.
Fortunately, we’re here to clear up some of those misconceptions. At Zachary Smith Arboriculture, we fertilize large Bay Area trees every day.
Our team is made up of certified arborists who know how to care for all types of trees – from small fruit trees to old-growth giants living in fertile soil.
In this blog, we’ll provide our top tree fertilization tips to help your trees stay strong and healthy.
Let’s dive in.
What is Tree Fertilization?
Put simply, tree fertilization helps trees grow. Contrary to popular belief, though, fertilizer is not “food.”
Trees produce their own food through the process of photosynthesis. Instead of replacing the tree’s natural food sources, the minerals and nutrients in fertilizer help support photosynthesis and healthy tree growth.
If a tree lives in soil that lacks key minerals or nutrients, fertilizer can help amend the soil and provide an adequate supply of essential nutrients.
That said, fertilizer will not save trees that are a poor fit for the climate, or that are unhealthy or carelessly planted, cared for, or watered.
Do I Need to Fertilize My Trees?
The answer is it depends.
To determine whether your tree needs fertilizer or not, consider the following factors:
Soil composition
Before you apply fertilizer, have your soil professionally tested.
A soil test (which can be done by an arborist or a local garden center) will determine the pH of the soil, as well as the levels of key nutrients present.
The results provide actionable information that allows you to choose the best fertilizer for your trees.
Tree growth
Is your tree growing normally? Does it look healthy?
Evaluate the tree for signs of inadequate growth, including the following:
- Stunted leaves
- Discolored leaves (pale green or yellow)
- Premature fall coloring and leaf drop
- Minimal twig growth
- Signs of dieback throughout the tree
Although these signs of poor growth are not always related to a need for fertilizer, they can indicate that your tree is lacking key nutrients. In other cases, the soil around the tree may be heavily compacted, or the tree may be affected by pests, insects, weeds, or diseases.
Rule these problems out before you decide to add fertilizer.
The age of the tree
If the tree is newly planted, fertilizer may help speed growth and encourage the tree to thrive. For best results, we recommend a slow-release fertilizer that will provide long-lasting nutrients.
Location
If your tree is planted in an area that is not fertilized regularly (such as a planting bed), it may need occasional fertilization. A tree planted in a yard that is fertilized regularly, on the other hand, will not.
What is the Best Time to Fertilize Trees?
Once you’ve decided that your tree could benefit from fertilization, the question becomes when? The following two seasons are best for fertilization:
Spring
- Fertilizing trees in the spring helps support new growth during the early growing season.
- Springtime fertilization also promotes a faster “green up,” which helps tree leaves stay vibrant throughout the growing season.
- Can provide essential nutrients that help a tree stay strong and avoid infestations by pests or diseases.
Fall
- Fertilizing in the fall helps the tree recover and store nutrients lost during a long, hot summer.
- Will promote root growth throughout the winter in climates where the soil does not freeze.
How to Effectively Fertilize Your Trees
When it’s time to fertilize your tree, follow this step-by-step guide for beautiful results:
1. Choose the right formula
Most fertilizers contain three primary nutrients: nitrogen, phosphorus, and potassium.
These nutrients mimic the makeup of healthy, fertile soil, and help support thriving trees.
Some fertilizers also contain amino acids designed to enhance the availability of nutrients, lock nutrients in, and prevent runoff during rain or watering.
To find the right fertilizer for your trees, choose one that’s suited to your region, and the type of tree(s) you’re fertilizing.
Some fertilizers are suited for oak and fruit trees, for example, while others work better for shade trees and pine trees.
2. Apply the fertilizer
Figure out how much fertilizer you need by following the application chart on the back of the bag.
Next, spread the fertilizer as close to the tree’s roots as possible.
There are a few ways to do that:
One way is to use a handheld auger and drill 12–15” deep holes every 2–3’ around the drip line of the tree (where the outer branches end). For large trees and mature trees, this could mean you’re drilling many holes across a large area.
Another option is to use a shovel to lift the sod and disperse the fertilizer below it. No matter which method you choose, be sure to apply the allotted amount of fertilizer evenly around the entire tree.
3. Water
Once you’ve applied the fertilizer, water the tree thoroughly. This is an important step, since water is what pushes the fertilizer down toward the tree’s roots and promotes absorption.
What is the Best Fertilizer for Trees?
As we mentioned earlier, there are many varieties of fertilizer for trees, and finding the right one for your landscaping will take a bit of research and detective work.
As a general rule, though, tree and shrub growth tends to be limited by nitrogen deficiencies more than any other nutrient. As such, trees usually react best to fertilizers with a 2-1-1 or 3-1-1 ration (nitrogen-phosphorus-potassium).
If you’re not sure you’ve found the right mixture for your tree, hire an arborist, or talk to the experts at your local garden center.
Can You Over-Fertilize Trees?
You can have too much of a good thing. When it comes to fertilizing trees, it’s possible to kill the tree if you apply too much fertilizer.
If you dump a large amount of quick-release nitrogen fertilizer on a tree, for example, you’ll wind up burning the roots and shocking the tree.
Because of this, it’s important to always follow the application directions of the fertilizer you choose, and to make sure that you’re not fertilizing trees too often each year.
Young, newly-planted trees should be fertilized annually, while mature trees will only need fertilization every 2-3 years to maintain healthy growth.
How Do Arborists Fertilize Trees?
If you hire an arborist to fertilize your trees, what can you expect from the process?
Here’s the step-by-step plan our team here at Zachary Smith Arboriculture uses to fertilize trees for our customers:
1. Assessment
First, our arborists will conduct a thorough assessment of your property. We’ll take soil samples, inspect watering and irrigation practices, and evaluate all the plants growing around the target trees.
If we suspect that there are pests or diseases present, we’ll send soil or plant samples to a lab to rule out imbalance or illness. This initial assessment gives us the information we need to develop a targeted management and fertilization plan for your trees.
2. Soil and irrigation remediation
Because irrigation is such an important part of proper fertilization, we’ll spend the next portion of the process assessing, improving, and remediating your soil and irrigation. We’ll make necessary changes to promote adequate irrigation and prevent over- or under-watering.
3. Application of fertilizer
Next, we’ll apply the fertilizer. We use complete, organic, slow-release fertilizers that are specially formulated to feed the soil at a microbial level. We never use synthetic fertilizers, which can harm or burn trees and negatively impact the soil biome.
We choose each fertilizer based on the species of tree and the region in which it’s growing, and measure all application amounts carefully.
4. Follow-up
Once we’ve fertilized the tree, we’ll schedule any needed follow-up appointments to continue correcting soil imbalances and ensuring ongoing nutrition for your trees and shrubs.
During these follow-up appointments, we’ll educate you about the health and care of your trees and give you the tools and knowledge needed to enjoy your most beautiful landscaping yet.
How Much Does Tree Fertilization Cost?
DIY methods of tree fertilization are generally less expensive than hiring a professional. You can purchase a bag of tree fertilizer for about $30-$50 per bag, while tree fertilizer spikes generally cost less than $20 for a box of six.
While DIY tree fertilization may be fine to give your trees a boost here and there, it is not the best option if you have trees that are sick, diseased, or failing to thrive.
When you invest in services from a professional arborist, you know you’re getting precision fertilization for a healthier, stronger tree and a more beautiful outdoor space.
Looking for a Professional Tree Fertilization Service in the San Francisco Bay Area? We’re Here to Help!
Your trees deserve bespoke fertilization that helps them reach their full potential.
Here at Zachary Smith Arboriculture, we help residential properties in Northern California – from Marin to Monterey – care for and enhance their trees and deliver targeted fertilization at each stage of tree growth.
To learn more about our services or to schedule your tree fertilization appointment, contact us today.
