The grand ol’ oak (Quercus) is a deciduous tree that has been present in many historic events throughout North America, and indeed the World. Producing acorns and ever-changing, seasonal color, this ornamental thrives in hardiness zones 7-10b, depending on the variety.
Oaks grow at a rapid rate of 1-3’ per year. Reached a mature size of 70’ tall and an astounding 135’, in width. For mature trees, fertilizing isn’t necessary beyond a certain point. But, if your trees aren’t quite there yet and need a boost, the best fertilizer for oak trees is just a quick read away.
- Best Oak Tree Fertilizers
- Choosing Fertilizer for Oak Trees
- Best Oak Tree Fertilizer Reviews
- 1. Jobe's Tree and Shrubs Fertilizer Spikes 15-3-3
- 2. Down to Earth Tree & Shrub Fertilizer Mix 4-2-4
- 3. Jacks Classic No.4 All Purpose Fertilizer 20-20-20
- 4. Scotts Tree Fertilizer Continuous Release 11-7-7
- 5. Espoma TR4 Tree-Tone 6-3-2
- 6. Espoma Organic Holly-tone 4-3-4
- 7. Shake 'N Feed Tree and Shrubs Plant Food 18-6-12
- How to Fertilize Oak Trees
- When to Fertilize Oak Trees
- Verdict: Best Fertilizers for Oak Trees
- FAQ’s Fertilizing Oak Trees
Best Oak Tree Fertilizers
For effective ways to nourish your oaks and increase vitality, be sure to read all the way to my FAQs. But, if you just need fast, reliable advice for the best fertilizer for oak trees, here are my top pick performers.
Best Fertilizer Spikes
Jobe’s Tree and Shrubs Fertilizer Spikes 15-3-3
Feeding your growing oak all season long for superb results is just one step away with the convenience of just a few easy-to-use and mess-free fertilizer spikes.
Best Organic Fertilizer Granules
Down to Earth All-Natural Tree & Shrub Fertilizer Mix 4-2-4
100% natural ingredients that will boost foliage growth and protect your oaks against damage from their humble sapling beginnings right up to maturity.
Best Fertilizer for Depleted Soil
Jacks Classic No.4 All Purpose Fertilizer 20-20-20
Help restore nutrient-depleted soil with this balanced NPK ratio of water-soluble feed. Suitable for a wide variety of year-round garden fertilizing requirements.
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Choosing Fertilizer for Oak Trees
To encourage lush foliage and an overall healthy oak tree, its specific nutrient needs in the early stages of growth must be understood and supported. These are not considered heavy feeders. But oak trees are susceptible to vascular issues if the fertilizer isn’t applied correctly.
Healthy, mature oak trees typically don’t need fertilizing at all. However, over time, soil can become depleted of nutrients or compacted. In which case, supplemental nutrients may be needed, to stimulate new growth and acorn production.
Phosphorus and potassium are necessary to support flowering and acorn development. Yet, nitrogen holds the highest nutrient value for oak trees. As they use it to trigger robust trunk and branch growth, followed by lush foliage. So, the best NPK for them will have a significantly higher percentage of nitrogen.
Oak Tree Fertilizer N-P-K Ratio
Now that you know what your oak trees need, your next step is to choose the right NPK formula to support them.
What is an NPK? Every fertilizer label includes a three-numbered N-P-K ratio. Indicating that product’s proportions of nitrogen, phosphorus and potassium.
For example, a 6-3-3 NPK has 6% nitrogen, 3% phosphorus and 3% potassium. Every plant requires these three elements for optimal health. Just in different proportions.
Soil pH and Nutrient Uptake
Each oak variety has its own pH preference. But, it’s usually somewhere within 3.6-7.0. It’s important to narrow down the best range for your specific Oaktree variety, though.
Why? When the pH is too low, nutrients become too accessible and are absorbed in excess of what the trees need. In pH that’s too high, the opposite happens. Nutrients become locked in the soil and unavailable to roots.
Granular Vs Liquid Fertilizer
Granular fertilizers are preferred among arborists. Indeed, citing a rapid infusion of liquid nitrogen can result in structural damage and “oak wilt” from burned roots.
Yet, liquids do have their benefits. When oaks are growing in poor soil, they immediately receive vital macro and micronutrients. Even if you regularly use slow-release fertilizers, a quick boost of liquid nutrients may benefit you during growth spurts, as buds set, or in times of drought.
Controlled Release Fertilizer Spikes
Spikes are slow-releasing and effective. Conveniently pre-measured, they’re easy to push into loamy soil. Nutrients are released as trees are watered or by rainfall. They also carry the added benefit of stimulating an increased resistance to disease and pests. Unused portions can simply be stored away.
Organic vs Synthetic Fertilizers
Deciding between these is simply a matter of personal preference. However, an understanding of how each works and affects your environment can support an informed decision.
Organics naturally increase soil fertility and nourish plants for longer, while encouraging proper aeration and drainage.
Synthetics are mass-produced using minerals and chemical compounds. They can boost rapid growth by providing higher levels of nutrients. On the flip side, they do little for a microbial activity or long-term soil fertility.
Best Oak Tree Fertilizer Reviews
I’ve had the opportunity to test several different fertilizer options on several different oak varieties with successful and, sometimes, surprising results. These are my picks for the top 7 performers, based on NPK results, versatility-of-use, and product features that accommodate different nutrient needs.
PROS
- Effective NPK for foliage, branch, and acorn growth.
- No wasteful runoff.
CONS
- May break if applied to hard soil.
Despite being labeled for evergreens, the NPK formula of 15-3-3 in these fertilizer spikes from Jobe’s can also benefit oak trees. Sending consistent, slow-release nourishment directly to the roots.
Applying these around your growing oaks will result in larger, more lush foliage and a strong tree structure, due to the higher percentage of nitrogen. As well as impressively vibrant fall color.
For easy insertion, I found it best to clear away all fallen debris from within the drip line, water the application area well, then tap the included driving cap with a rubber mallet, until the top is level with the soil surface.
How To Use: Insert the recommended number of spikes within the tree’s dripline, in early spring and late fall, and water well.
PROS
- Effective on all flowering plants and trees.
- Formulated for vigorous growth, abundant fruit, and healthy plant stock.
CONS
- May attract pets and wildlife with the organic smell.
This completely organic formula nourishes mature trees and new saplings, alike. When I got to help plant some new oaks for Arbor Day, I worked 2 cups of these granules into the backfill soil.
Within weeks, I was surprised to see how quickly new growth had sprouted. Equal parts of nitrogen and potassium encouraged balanced structure, foliage growth, and healthy root establishment.
The 100% natural list of ingredients in these granules is fortified with 11 types of mycorrhizal fungi, making this my pick for the best organic fertilizer. How To Use: For new saplings, add ½-1 cup per hole, and mix into soil and water in well. For mature trees, side-dress ¼-½ cup per plant, once each month during the growing season.
PROS
- Optimal nutrition for acorn production and vibrant foliage.
- Dissolves faster and cakes less than other top brands.
CONS
- May give off an earthy odor.
After testing the soil around a row of ailing, mature oaks, I discovered the soil had been severely depleted of nutrients, over time. And soil compaction made it hard for nutrients to reach the roots.
Using an irrigation system, the balanced nutrition in these water-soluble granules from Jack’s Classic infused the soil around them with high enough levels of nutrients to revitalize those tired trees. Yet, not enough to hurt them.
Within a week or so, foliage color became more vivid and new growth, that had been non-existent before, began to appear like magic.
How To Use: For best results, mix with warm water. Then, apply 1 tablespoon per gallon of water used. Repeat every 10-14 days.
PROS
- Includes sulfur to raise soil acidity and improve nutrient absorption.
- Nourishes for two full months.
CONS
- May attract pets and wildlife with organic smell.
I found these granules to be highly effective on both evergreen and deciduous trees like oaks. Especially when the foliage color begins to yellow. Chlorosis is a symptom of nitrogen deficiency and this 11-7-7 NPK worked wonders on an ally of young oaks that clearly needed a boost.
As the yellowing disappeared, new buds developed. Resulting from the generous 7% of phosphorus and potassium, as well as pH balancing elements.
If you have a perennial garden full of acid-loving plants like azaleas and hydrangeas, then this versatile formula is for you too.
How To Use: Work 1 cup of granules into the soil for every 35 square feet within the dripline. Then, water thoroughly. Repeat every two months during the growing season.
PROS
- Formulated with exclusive Bio-tone Microbes.
- Provides 100% organic nourishment for 6 months.
CONS
- Must be stored in a cool, dry place.
These effective, slow-releasing granules from Espoma may be labeled for fruiting trees, but the increased nitrogen in the 6-2-3 NPK, I’ve discovered, is perfect for acorn production on oaks. Especially if you want a few more for feeding the wildlife and crafting projects.
I also found that this works best when applied below the soil’s surface, within the tree’s dripline. I used a small auger to make holes around some mature oaks that had begun to fail. I poured the granules in, and not only did they increase resistance against environmental stresses and pests, but new growth quickly sprouted.
How To Use: Apply the recommended amount per trunk diameter. Once in spring and again in fall. Watering well after each application.
PROS
- Increases soil fertility and acidity while nourishing trees.
- Provides 100% organic nourishment for 6 months.
CONS
- May require larger applications than other options.
I tested this 2nd Espoma option on one grand oak that didn’t seem to be responding to other fertilizers. Its size and condition suggested the soil had been depleted of nutrients and acidity.
Formulated for acid-loving plants, these slow-release granules lowered the soil pH, increasing acidity around this beautiful oak. Improvement seemed almost immediate! Because now it has easier access to nutrients.
Containing proprietary Bio-Tone microbes, this Holly-Tone mix is beneficial for all evergreen and deciduous trees that prefer acidic soil. As well as acid-loving shrubs, fruiting trees, and berry bushes.
How To Use: In spring, use an auger to create holes 12” deep and apply 1lb, evenly within the dripline, per inch of trunk diameter. Water thoroughly and repeat in fall.
PROS
- Includes organic kelp and earthworm castings.
- Added microbes for healthy nutrient absorption.
CONS
- May be sold at a higher price point than other options.
This is perfect for over-sized oaks that need a strong infusion of nitrogen, to improve foliage growth and strengthen trunk and branch structure.
With a higher percentage of nutrients, this NPK will revive depleted soil and increase acidity around evergreens and flowering trees, and shrubs. Improving absorption of the provided nutrients.
While not considered organic, this shake n’ feed option does contain beneficial soil microbes that convert nutrients into a form that oak trees can more easily absorb and metabolize.
How To Use: Shake granules evenly around the soil with the tree’s dripline, at a rate of 2 tbsp per 4 ft of soil surface. Water thoroughly and re-apply every three months during the growing season.
How to Fertilize Oak Trees
Oak trees are relatively easy to care for and are fairly low maintenance. In natural environments (where the oak grew on its own), they may not require fertilization, at all. Having adapted to what is naturally provided in their environments.
However, there will be times when they need it to stay healthy. Newly planted saplings, large trees that have been moved into new landscapes, and even mature oaks that have absorbed all available nutrients, will fall into this category.
As mentioned, slow-release fertilizers are considered more beneficial than fast-acting liquids, because oak trees are sensitive to being over-fertilized.
Once you’ve determined the need, spread your fertilizer evenly within the dripline. Even distribution prevents roots from bunching up in one spot and allows for easier nutrient uptake.
Use The Tree Drip Line
Your tree’s drip line is a convenient measuring tool for determining where to apply fertilizer. The drip line is the distance between the leaf tips on one side to the leaf tips on the other.
Application rates are commonly recommended in lbs per 1000 sq ft. How do you calculate how much you’ll need? Example: A 5’ wide drip line would roughly span 25 sq ft of soil space. 1000 / 25 = 40, 2-4 lbs of fertilizer / 40 = .05 – .10 lbs of fertilizer for that tree.
Avoiding Oak Tree Fertilizer Burn
The most common cause of fertilizer burn is over-application. Testing your soil will determine if your oak tree actually needs it. And taking measurements will ensure the proper dosage.
It’s also important to remember that in addition to vital nutrients, synthetic fertilizers contain salts. When over-applied, these salts can siphon moisture from plants and trees, causing dehydration and burned foliage. Excess nitrogen can burn roots, causing structural damage and “oak wilt”.
When to Fertilize Oak Trees
Hardwood Oaks are deciduous, shedding their leaves in late autumn. These decompose and contribute nutrients to the soil where they fall. Yet, the bigger an oak grows the more nutrients it may need, depending on environmental conditions.
If your oak needs fertilizing, the most beneficial time to apply it is just as the tree is coming out of winter dormancy and ramping up for new growth. Added nutrients, at this time, will provide the kind of support oak trees need for lush foliage and abundant acorn production.
The second dose in fall will increase tolerance against winter conditions and help maintain vital internal processes, making new spring growth more robust.
Fertilizing Oak Trees In Winter
Every plant, shrub, and tree goes into, at least, a partial dormant state in winter. Cold-climate oaks will go fully dormant. Fertilizing these in winter may actually harm them. They’re not able to metabolize it, making burning more likely.
Yet, most oak varieties are native to warm climates. They’ll continue to grow, albeit slower, in winter. Fertilizing these late in the year has proven beneficial for healthy spring growth.
How Often to Fertilize Oak Trees
Most fertilizers are made to accommodate lots of different plants, so make sure that the recommended frequency of your fertilizer choice meets your oak’s specific needs.
One application of a slow-release fertilizer, like Scotts Continuous Release Granules or Espoma’s Organic Holly-tone will last a full growing season.
But if your trees need a quick boost Jack’s Classic water-soluble fertilizer or Down to Earth’s All Natural fertilizer mix will provide that with monthly applications.
Verdict: Best Fertilizers for Oak Trees
It looks like we have our verdict! The most effective fertilizer for oak trees will depend on soil conditions and tree age.
You probably won’t have to worry about mature ones unless a soil test reveals a nutrient deficiency. But new saplings and large trees transplanted into new landscapes will definitely appreciate the extra support.
A fertilizer higher in nitrogen such as Jobe’s Tree and Shrub Fertilizer Spikes with their 15-3-3 NPK ratio will provide what your oaks need to sustain optimal health and growth.
Best Fertilizer Spikes
Jobe’s Tree and Shrubs Fertilizer Spikes 15-3-3
Feeding your growing oak all season long for superb results is just one step away with the convenience of just a few easy-to-use and mess-free fertilizer spikes.
When acorns are scarce, Down to Earth All-Natural Tree & Shrub Fertilizer with an NPK of 4-3-4 will encourage vigorous foliage and bud development.
Best Organic Fertilizer Granules
Down to Earth All-Natural Tree & Shrub Fertilizer Mix 4-2-4
100% natural ingredients that will boost foliage growth and protect your oaks against damage from their humble sapling beginnings right up to maturity.
Liquids or water-soluble feeds should only be used when ailing trees need quick nutrients or when soil is depleted of nutrients, in which case Jacks’s Classic All-Purpose Fertilizer with its 20-20-20 NPK will provide the boost your oaks need to begin thriving again.
Best Fertilizer for Depleted Soil
Jacks Classic No.4 All Purpose Fertilizer 20-20-20
Help restore nutrient-depleted soil with this balanced NPK ratio of water-soluble feed. Suitable for a wide variety of year-round garden fertilizing requirements.
