3 Best Oak Tree Fertilizers (and How to Use Them)

Oak tree

Oak trees are truly breathtaking, with their wide-open canopies that spread across a landscape and with building-sized heights that tower over you; oak trees are just simply full of life. However, for them to be full of life and grow successfully, it’s important to know that oak trees sometimes need to be fertilized!

In order for oak trees to grow successfully, they need to be fertilized. The ratio, 12-4-8 – 12% Nitrogen, 4% Phosphorus, and 8% Potassium, is considered an ideal mix when choosing a fertilizer for an oak tree. Fertilizer helps the oak tree grow and produce acorns. 

You may have heard that oak trees are easy to take care of and may not need a lot of maintenance to grow, and that’s usually true – however; young oak trees, transported oak trees, and even in some instances, mature oak trees, all will benefit from fertilizer. 

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What is Fertilizer for Oak Trees?

Think of fertilizer to plants as vitamins are to people. Sometimes plants and oak trees need a little bit of extra help to get them to where they need to be, and this is where fertilizer comes into play. 

Fertilizer is any material that is used to give a plant and oak tree nutrients. Fertilizer can be inorganic, organic, natural, or synthetic and usually contains three key ingredients – nitrogen, phosphorus, and potassium when used in agriculture. 

Fertilizer can help plants and crops grow bigger, faster and can actually make a plant produce more food than it would without fertilizer. In an oak tree’s case, fertilizer will help it produce more acorns. 

However, not all fertilizer is the same – and there are some fertilizers that are better for certain plants than others. 

Different Types of Possible Oak Tree Fertilizer

There are many different types of fertilizers – all of which do different things. Depending on which type of plant you are looking for or the problem you are trying to solve, there is a fertilizer that will help with your oak trees issue. 

Mineral Fertilizers 

Mineral fertilizers are key to giving the soil and plants the nutrients they need to help them grow as healthy as possible. Mineral fertilizers take naturally occurring minerals and transform them for use as fertilizer. 

There are nitrogen fertilizers, phosphorus fertilizers, potassium fertilizers, calcium fertilizer, magnesium fertilizers, and even a combination of nutrient fertilizers – all of which are considered mineral-based. 

Organic Fertilizers 

Organic fertilizers are another type of fertilizer that is made from organic matter. It is used to enhance the growth of crops and can actually help in deterring pests and disease from the soil.  

It is said that using an organic fertilizer can create higher seedling biomass and can significantly improve the soil fungal to bacterial ratio as well as soil enzyme activity in your soil. 

Inorganic or Synthetic Fertilizer 

Inorganic or synthetic fertilizer is exactly what it seems like – it’s synthetic minerals and chemically based fertilizer. Whatever your plant specifically needs – there is an inorganic formula for it! 

However, when using any of these fertilizers, it’s important to always make sure you are using the correct dose because too much can cause harm to your plant or oak tree. 

How Does Fertilizer Work?

No matter the type of fertilizer that your plant needs, all fertilizers typically work the same.

Whether sprayed directly onto leaves or applied to the soil – the plant will go through a metabolic process while taking in the nutrients that the fertilizer provides. Think of the plant absorbing the fertilizer and getting the nutrients it needs!

When we talk about fertilizing plants, there are many options out there for many different needs and to solve many different problems – however, today, we’re going to focus on oak trees and the best fertilizer for them!

Should I Fertilize My Oak Trees?

Big oak tree in summer green meadows, sunset time with red sky in background

The answer to whether or not you have to fertilize your oak trees or not is – yes, and no! I know it’s confusing – but we will break it down for you. Oak trees benefit from fertilizer, and depending on the stage of life that it is in, fertilizer may be a necessity.

Mature Oak Trees Don’t Always Need Fertilizer

Mature oak trees do not always need fertilizer, and if added unnecessarily, they can actually cause the tree more harm than good. 

When oak trees are mature, they typically already have a good system going. The leaves that fall from the oak are actually the exact organic material that oaks need!

If you let the leaves stay by the tree, rather than rake them up, the leaves will eventually decompose into the soil, and the oak tree will eat them right up – giving the tree all viable nutrients!

However, on the contrary – if your oaks leaves are yellow or brown, blistered, have a different color around the perimeter, or has a lot of holes in them – your oak tree may have a disease, and therefore, if your oak absorbs those fallen leaves, your oak tree will become unhealthy

Adding fertilizer to a mature tree may actually be too much for the tree to handle. The oak tree is already getting plenty of nutrients the way it has been for many years. It is so used to doing its own thing to survive that adding any extra nutrients may throw off its balance and harm it!

The difference between a mature oak and a young oak is that when a young tree is growing, it doesn’t hasn’t built its roots. Physically, the tree has roots – but the roots are not grown deep enough to maintain stability. And because of that, the oak tree doesn’t have a consistent, stable routine to help keep its health.

 A young oak tree is still growing and needs assistance along the way. 

It’s Important to Fertilize Young Oak Trees 

The most important time to fertilize an oak tree is when it is young! An oak tree that was just planted would benefit greatly from fertilizer. The thing to understand about fertilizer is that it’s important to add when the tree is actually growing – this also counts for the time of year you fertilize, but we will get to that in a bit!

Newly planted oak trees require love and care, and nutrients! Adding fertilizer into the soil will be absorbed by the tree and its roots to help it grow to its highest potentials. 

Because young oak trees are so new to the world, it’s important to assist them in establishing a proper foundation, and because it takes some time to grow deep, sturdy roots, adding fertilizer can help speed up the process while helping it gain strength. 

Add Fertilizer to Transported Oak Trees After Roots Establish 

Now you may think – since the roots aren’t established, shouldn’t I be fertilizing the tree right away? The truth is – not really. There is a good chance that a transported oak tree already established a good routine somewhere else, and therefore shocking it with fertilizer can actually do harm. 

Taking a tree that has already established roots and planting it somewhere else is definitely a big change for the tree. The tree is definitely going to be in a shock-like state, and until it settles into its new environment – it should be left alone in terms of fertilizing. 

A good way to understand this is – imagine being nervous and being told to react calmly – it’s just not going to happen! When your tree is in this new heightened state, the best thing to do is to leave it alone – until it has some time to adjust. 

However, if you know that your oak tree is being transported, much like a new oak tree in a nursery, it may be good to start feeding it with fertilizer so that it gains the energy and strength needed to survive the transport!

Fertilizer Helps Oak Trees in a Nursery Grow

Think of a newborn baby. They have no idea what they’re doing, and they need your assistance – it’s the same with an oak tree in a nursery. 

Not only are oak trees in a nursery young, but they are being prepared for transport – so it’s important to give them the necessary nutrients so that they can be successful in their new environments. 

Giving your oak trees fertilizer truly depends on the stage of life they are in, but for mature oaks – it also depends on the state of health that they are in. 

How to Tell If My Mature Oak Tree Needs Fertilizer?

Background of ancient old oak tree in middle of riped agricultural fields and cloudy blue sky.

The thing about oak trees that makes them such a common tree is that they are strong, stable, and really predictable.

Oak trees are not susceptible to many diseases, although they do come up from time to time, and once matured – oak trees are easy to grow and require little to no maintenance. 

However, sometimes oak trees get unhealthy, and there are signs that you can look out for to see if your oak is healthy. If your oak tree isn’t healthy, you may need to add some fertilizer into the mix. 

What Does a Healthy Oak Tree Look Like? 

It sounds redundant – but it’s the truth. A healthy tree will have a full canopy of leaves, green foliage all year except in the fall, bark that looks together and has a strong, stable appearance, and branches that produce leaves and are flexible to the touch. 

A quick way to check to see if your oak tree is healthy is by taking a branch and bending it! A healthy, live tree will bend and feel flexible, while an unhealthy tree’s branch will break when bent!

Although, there are also some easy ways that can help you determine if your tree is unhealthy.

You can read the full symptoms of a dying oak tree here.

What Does an Unhealthy Oak Tree Look Like?

There are five signs to look out for that can easily help you determine if your oak tree is unhealthy. 

  1. Yellow or Brown Leaves
  2. Thinning Canopy 
  3. Peeling Bark
  4. Brittle Branches
  5. Rotted Roots

If you notice any of these signs, you may want to call a professional or do some research to see what the underlying issue for the decline in health may be.

Additionally, you can read our full guide on what may be wrong with your oak tree here.

Oak trees are resilient, but sometimes, they do need some extra care, and if your oak is experiencing any of these symptoms, it may be calling for some help! This is when fertilizer may be just the answer. 

3 Best Fertilizers for Oak Trees 

Whether you have a new tree, a transported tree, or a mature oak tree that needs some extra care – there is a fertilizer for you! However, oak-specific fertilizers typically follow the N-P-K ratio and contain three mineral ingredients: nitrogen, phosphorus, and potassium – all of which are great for your oak! 

The N-P-K ratio is the number you see on a fertilizer bag and refers to the following three ingredients.

Nitrogen Is the Most Important Nutrient for Oak Trees

Nitrogen is arguably the most important nutrient for oak trees. It is necessary for plant growth and helps regulate any vegetative growth. Nitrogen is a part of amino acids and chlorophyll, and because of this, it is part of the process of enzymatic reactions that take place in the tree. 

If you are looking to fertilizer an oak, it is essential to find something with a higher percentage of nitrogen – try out HastaGro 12-4-8 Liquid Lawn Food Plus.

Phosphorus is A Key Nutrient for Oak Growth 

Phosphorus is the second key nutrient that helps our oak trees grow. Contained in many fertilizers – phosphorus is added because it helps plants grow bigger, stronger, and fuller by strengthening their root systems and promoting flowering. 

Being a structural component of both DNA and RNA, phosphorus carries important information on a molecular level that helps oak trees thrive. 

If you are in need of phosphorus-rich fertilizer, you may want to check out Burpee Organic Bone Meal Fertilizer.

Potassium Helps Oak Tree Growth Growth

Ah yes, potassium for your oak tree.

Potassium is also another beneficial key mineral in fertilizers, especially for oaks. Although potassium doesn’t impact the plant directly – it indirectly functions as a component that activates an enzymatic reaction – thus, that reaction becomes an essential part of the plant growth. 

Another great option for an oak fertilizer is Miracle-Gro Liquid All Purpose Plant Food Concentrate.

How to Fertilize an Oak Tree

Now that we know some of the best ingredients for your fertilizers, it’s time to learn how to actually fertilize your oak tree – and the best time to start is right before it rains or before you are watering! 

Before adding the fertilizer, make sure that you are not adding the mix within a foot of the tree’s trunk. Staying a healthy distance of about a foot away will help the tree absorb the fertilizer better. 

There are a few methods you can use to fertilize your oak tree: you can spread the fertilizer to cover two-thirds of the root zone, or you can create holes into the ground surrounding the tree’s drip line, about a foot and a half apart, and place the fertilizer into the holes! 

After you add the fertilizer, it is always best to water the area. Adding water will help the fertilizer move within the soil and be absorbed by the roots. 

When adding fertilizer, it is always best to read the directions on the product to see the dosing. Dosing varies and depends on the ingredients and the percentages of those ingredients. If you are unsure of what to do – it is always best to check in with a professional to ensure your tree’s health. 

When is the Best Time of Year to Fertilize an Oak Tree?

The best time of year to fertilize is in the mid-spring – and this is actually a general rule of thumb for any type of plant and oak tree. The reason why spring is the best time to fertilize is because the soil is typically warm and dry, and warm and dry are ideal conditions for fertilizer to be effective. 

The nitrogen specifically in fertilizer does the best in warm and dry soil, and being the key ingredient for the plant’s health, it is important to add it during this time to prevent any nitrogen loss. 

The reason spring is also the best time is that it is when our trees come out of the dormant season and start to grow. With mild temperatures and not too many extreme weather conditions, an oak tree can start to truly flourish – as we said earlier, while a tree is actually growing – it’s the best time to add fertilizer. 

It is not recommended to add fertilizer in the summer because of its extremely hot temperatures. Trees actually don’t grow that much in the summer, and because of that, adding fertilizers will actually do more harm than good, as the plant doesn’t need all those extra nutrients during this time.

The fall also isn’t recommended, as this is when our trees and plants are starting to settle down for the winter. In the fall, the lawns and plants start to become dormant, and they will not absorb any fertilizer that lays in the soil – this can actually lead to a high risk of nitrate leaching.

If you’re looking to plant, you can read our guide on the best time to plant an oak tree here.

Wrapping it Up 

All in all, your oak trees may need fertilizer from time to time. It’s always great to check with a professional if your mature oaks are not flourishing, and it’s always best to add fertilizer to young and growing oaks.


“The Effects of Chemical and Organic Fertilizer Usage on Rhizosphere Soil in Tea Lin, W., Lin, M., Zhou, H., Wu, H., Li, Z., & Lin, W. (2019). The effects of chemical and organic fertilizer usage on rhizosphere soil in tea orchards. PloS one14(5), e0217018.

Timing Fertilizer Application on Long Island. www.dec.ny.gov/docs/water_pdf/ffstiming.pdf. 

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