Trees and shrubs are an essential part of any landscape, providing beauty, shade, and habitat for wildlife. However, like all living things, they require proper care and maintenance if we are to get the best from them and one crucial aspect of tree and shrub care is fertilization.
Fertilizer provides essential nutrients that trees and shrubs need to grow healthy and strong. But with so many different types of fertilizer available, it can be challenging to know which one is right. In this post, I’ll cover everything you need to know about fertilizing trees and shrubs, including when to fertilize, what type of fertilizer is best, and how much to apply.
- 1. Jobes Tree and Shrubs Fertilizer Spikes 15-3-3
- 2. Down to Earth All Natural Tree & Shrub Fertilizer 4-2-4
- 3. Espoma Tree-Tone Organic Tree Fertilizer 6-3-2
- 4. Miracle-Gro Flowering Tree Fertilizer 18-6-12
- 5. Jobe's Evergreen Tree Fertilizer Spikes 13-3-4
- 6. Osmocote Smart-Release Tree Food 15-9-12
- 7. Scotts Fertilizer for Trees And Shrubs 11-7-7
- 8. Miracle-Gro Tree & Shrub Spikes 15-5-10
- 9. BioAdvanced Shrub and Tree Food 2-1-1
Choosing Whether To Apply Fertilizer
Before deciding to apply any type of fertilizer it is important to establish if there is a need. After all, the purpose of fertilizing is to supplement the nutrient value within your local soil, offering the tree optimum growing conditions. If the optimum growing conditions are already met then no fertilizer would be required.
Testing The Soil
I recommend you test the soil for two things, nutrient balance, and soil pH, as they go hand in hand. If the soil pH is incorrect for the variety of trees or shrubs that you are growing, the plant will not be able to absorb and transport the full spectrum of nutrients it requires for healthy growth.
For example in alkaline soils, where the pH is above 7.0, iron becomes less soluble and therefore less available for plant uptake. This can lead to iron deficiency, which manifests as yellowing leaves with green veins, a condition known as chlorosis. Most plants, including trees, prefer soil pH between 6.5 -7.0.
Testing the soil pH is critical, and then amending it with an application of sulfur or lime to adjust the soil pH level to fall within the range required for the tree or shrub that you are growing.
Laboratory soil test kits can also analyze soil quality and identify nutrient deficiencies in nitrogen phosphorus or potassium, as well as trace minerals such as iron, magnesium, and calcium amongst others. Allowing you to tailor the fertilizer selection to fit your requirements.
Signs of Poor Soil
Typically, it’s obvious to see when poor soil is holding back healthy tree growth, due to the visible symptoms.
- Discolored Leaves that turn yellow, brown, or drop prematurely. This is often a sign of nitrogen deficiency or trace minerals such as iron or magnesium.
- Weak or Slow Growth is often caused by poor-quality soil with low nutrient value or incorrect pH.
- Poor Flower or Fruit Production can be a good indication that the tree is lacking phosphorus or potassium.
- Deteriorating Bark is a symptom of a distressed or weak tree, which may be due to insufficient nutrients. However, there could be other causes such as pests or diseases.
Once you understand your soil, and what the growing condition is for your tree, you can make an informed choice on the best fertilizer to use and in what quantity to apply it. Different trees need different nutrients, at different times of their growth cycle and throughout a single season.
Nutrients Requirement for Trees and Shrubs
Trees and shrubs require a broad range of nutrients to grow and thrive. Here are some of the key nutrients that trees and shrubs need:
Nitrogen (N) is an important component of amino acids, which are the building blocks of proteins. Proteins are necessary for plant growth and development, including the production of new leaves, stems, flowers, and fruits.
Phosphorus (P) is necessary for several plant processes, including photosynthesis, energy transfer, and cell division. It also helps plants to develop strong roots and flowers, as well as improving their ability to resist stress.
Potassium (K) regulates water balance and helps trees transport sugars and other nutrients. It also plays a role in photosynthesis and increases resistance to drought and disease and pests.
- Calcium plays a critical role in cell wall development and nutrient transport within plants.
- Magnesium plays a key role in photosynthesis and overall plant health.
- Iron is necessary for the production of chlorophyll, which helps plants produce energy from sunlight.
- Manganese helps plants absorb other nutrients more efficiently and also aids in photosynthesis.
- Zinc is important for enzyme function, protein synthesis, and hormone regulation within plants.
- Copper helps with photosynthesis as well as enzyme function within plants.
All of these nutrients can be supplied to trees and shrubs through fertilization or by supplementing soil with organic matter such as compost or manure.
Identifying Symptoms of Nutrient Deficiency
Nutrient deficiencies often manifest as distinct visual symptoms, such as:
- Yellowing leaves (chlorosis) due to iron, nitrogen, or magnesium deficiency.
- Leaf curling, wilting, or necrosis resulting from calcium or potassium deficiency.
- Stunted growth or reduced leaf size due to phosphorus deficiency.
- Poor fruit or nut development from insufficient boron, zinc, or manganese.
Types of Tree Fertilizer
For the majority of applications, you will choose from either a solid or liquid fertilizer, each having its own benefits.
Solid fertilizers come as granules, pellets, powders, or sticks. They are easy to handle and apply and can be stored for extended periods. They are generally applied as a top dressing or mixed into the top layer of soil, giving a slow or controlled release of nutrients.
Liquid fertilizers can be applied directly to the plant’s leaves or roots and they provide a quick nutrient boost. They are water-soluble or liquid concentrates and are applied whilst watering. A few popular liquid fertilizers include fish emulsion, seaweed extract, or compost tea.
Controlled-release fertilizers are designed to release nutrients gradually over time, offering a more sustained and efficient delivery system. These fertilizers can be particularly beneficial in environments with fluctuating weather conditions, where rapid nutrient loss may occur.
Organic fertilizers are derived from natural sources such as compost, manure, or bone meal. They provide essential nutrients while also improving soil structure and promoting beneficial soil microorganisms. Organic fertilizers are an eco-friendly option for tree fertilization.
The Best Fertilizers For Trees and Shrubs
The ideal fertilizer for trees depends on various factors such as the tree species, soil type, and age of the tree. However, most trees benefit from a slow-release fertilizer that provides a balanced mix of macronutrients N-P-K 16-4-8, 4-2-4, or 15-3-3 (nitrogen, phosphorus, and potassium) as well as micronutrients such as iron and magnesium.
I generally use either Down to Earth All Natural Tree & Shrub Fertilizer 4-2-4 or I am equally happy using the fruit tree fertilizer 6-2-4 as a top dressing, or if I’m transplanting new trees I will mix it into the soil in and around the planting hole, to keep it within close proximity of the tree roots.
These fertilizers have a base blend of natural organic products including bone, soybean, and feather meal with supplemented rock phosphate, kelp, and basalt. It’s a good complex blend of natural ingredients.
Or for mature trees, or trees that are well established I use Jobes Tree and Shrub Fertilizer Spikes 15-3-3 for deep root fertilizing, which offer a fit-and-forget type approach allowing me to focus on other aspects of my garden. So let’s take a look at each option in more detail.
1. Jobes Tree and Shrubs Fertilizer Spikes 15-3-3
Best Deep Root Fertilizer
- Easy to use and great for foliage
- Best value for money product
- Ideal for long-term tree and shrub care
- Excellent oak tree fertilizer and other deciduous trees
- Spikes need to be kept dry once the packet opened
This slow-release fertilizer from Jobe’s contains easy-to-use tree fertilizer spikes. The shape of the spikes is what makes them so easy to apply as all you have to do is insert them into the ground where needed and cover them with soil. Jobe’s Tree spikes are one of my favorite fertilizer products, including this standard version, the spike for citrus fruit, or evergreen tree fertilizer spikes. They have served me very well.
Since the spikes work as a slow-release feed, it makes them ideal for newly planted and young trees. If applied at the beginning of the season (early spring), the spikes will last all the way to the end of the growing season, eliminating any waste, and saving you money and time.
The pre-measured fertilizer sticks have an N-P-K 15-3-3 suitable for beautiful leafy foliage. Perfect for deciduous trees and shrubs making it a great oak tree fertilizer, as well as an excellent product for dogwood, elm, birch, maple, and poplar to name a few more. Making it the best fertilizer for trees and shrubs. Check out Jobes Tree Spike’s latest price on Amazon.com.
How to use: water the soil thoroughly before application. Place the appropriate number of spikes along the tree’s drip line, (for every two inches of trunk diameter, use two spikes). For shrubs, use one stick for every 3 feet of height.
Customer Reviews: Across all forums and retail outlet customer reviews, this product has impressed me. With just how easy it is to apply in these convenient spikes. Picking up an average user score of 4.6/5.
2. Down to Earth All Natural Tree & Shrub Fertilizer 4-2-4
Best For Top Dressing
- Packed full of natural quality organic ingredients
- Gentle enough to use directly on young tree roots
- Natural ingredients will smell slightly
Down to Earth Tree and Shrub Fertilizer is formulated for general tree maintenance and for use when planting bare-root or container-planted trees.
Made with a base blend of bone, soybean, and feather meal with supplemented rock phosphate, kelp, and basalt. It’s a good complex blend of natural ingredients that is kind to your garden. The slight downside of this blend tends to be the smell, which can attract some unwanted wildlife.
How to use: The best way to apply this tree fertilizer during planting is to simply mix 1-3 cups of fertilizer into the backfill soil. This natural compound is delicate and will not burn young trees or shrubs’ roots. For existing trees either dig in or pour into holes drilled 3-6″ deep around the tree drop line to avoid a run-off.
Check Down To Earth’s latest price here
Customer Reviews: Down to Earth is a lesser-known brand, but appeals to the eco-minded gardener and homesteaders. We have been a fan of their products for some time and would highly recommend their product to anyone looking to be organic. Scores 4.5/5.
3. Espoma Tree-Tone Organic Tree Fertilizer 6-3-2
Best For Fruit Trees
- Delivers outstanding results
- Organic and one of our favorite products
- Digging is required during application for the best results
Espoma Tree-Tone Tree Fertilizer is a long-lasting slow-release organic plant food that contains bio-tone microbes. It’s 100% natural and organic and delivers outstanding results with its N-P-K 6-3-2 formulation.
For best results, I like to use this product twice a year in the standard spring and fall windows. It’s not as easy to apply, requiring some digging, but the results are excellent. This is a good all-rounder because it is formulated for use as an apple, pear, and cherry tree fertilizer as well as for use with chestnut, walnut, willow, and cypress trees.
Despite the additional work required to apply this product it still comes right at the top of the list, as the second-best fertilizer for trees and shrubs. Available to buy online here.
How to use: For smaller trees or shrubs simply sprinkle the product over the ground equal to the root spread. This can be estimated by matching the diameter of the branch spread. For large trees make drill holes around the drip line of the tree, approximately 3-6″ deep and 2-3″ in diameter, and fill with fertilizer. Water thoroughly.
Customer Reviews: Despite its more specialist nature this tree fertilizer has gained a loyal following and customers gave this product an incredible 4.7/5 based on performance. Probably the best product on the market, despite the extra work required to apply. An excellent fertilizer for fruit trees.
4. Miracle-Gro Flowering Tree Fertilizer 18-6-12
Best For Flowering Trees
- An excellent choice for flowering trees, as well as a fertilizer for palms, and ferns
- An easy apply a slow-release fertilizer
- Great for use indoors and outdoor
- Nothing of note
The Miracle-Gro Shake ‘N Feed tree and shrub fertilizer is a slow-release tree and shrub food for all types of plants, flowers, trees, and shrubs. What I love about this star product is the fact that you can conveniently use it on both indoor and outdoor plants and as you can tell by its name is super easy to use. Just shake it onto the soil and rake it in. Perfect for trees and shrubs, but also a great all-around fertilizer.
With its excellent formula of long-lasting, all-purpose plant food, your trees and shrubs will enjoy all the nutrients they need at the beginning of the growing season for up to 3 months. Its relatively high levels of potassium mean this is a great product for flowering and fruiting trees and shrubs. I use it as a fertilizer for blueberry bushes.
The slow-release formula can be used to help the root and stem strength of the shrubs, with natural ingredients such as earthworm castings, feather meal, and kelp to keep plants and trees thriving all year round. Producing luscious green foliage and colorful flower blooms. This is one of our top picks for general tree and shrub use. You can buy this fertilizer online here.
How to use: simply mix the granules with the topsoil for in-ground or container use, then water thoroughly. Alternatively, simply rake the tree fertilizer into the topsoil ahead of any forecast rainy weather.
Customer Reviews: Over 4,000 satisfied reviews from customers who have seen excellent results awarding this product 4.6/5.
5. Jobe’s Evergreen Tree Fertilizer Spikes 13-3-4
Best For Evergreens
- Will bring browning evergreens back to a strong green foliage
- Easy to use and great value
- The best fertilizer for pine trees
- Spikes need to be kept dry once the packet opened
As part of the same product range as the Jobe’s Tree And Shrub Fertilizer Spikes work in exactly the same way. A slow-release 4″ fertilizer spike that is perfect for spring and fall applications. This product range is available in packs of 5, 9, 15, and 150 spikes. A pack of 15 should be enough to feed 3 trees for a whole season. Check the latest prices here.
With an N-P-K of 13-3-4, making these spikes are a perfect pine tree fertilizer and the perfect choice for firs, spruce, cypress, holly, western cedar juniper, and acid-loving ornamental evergreens. This formula is slightly lighter and tailored more towards evergreen feeding requirements. But could be used with success on all non-flowering trees and shrubs.
How to use: water the soil before application. Hammer or push the required number of spikes along the tree’s drip line, (for every two inches of trunk diameter, use two spikes). For evergreens use one stick for every 3 feet of height.
Customer Reviews: Just like the standard tree and shrub fertilizer spikes from Jobe’s, we see great customer feedback for the specialist evergreen tree fertilizer spikes. Scoring 4.6/5. Making it the best fertilizer for evergreens.
6. Osmocote Smart-Release Tree Food 15-9-12
- Super easy to apply
- Ultra-slow release fertilizer
- Great for trees and shrubs in containers
- Not suitable for large garden trees
Okay, not a specialist tree fertilizer but without a doubt one of the most popular general-purpose fertilizers on the market with excellent results. Osmocote Plus slow-release formula is a high-quality product that incorporates a very clever design. A small linseed ball outer shell (often mistaken for plastic) that houses a 15-9-12 nutrient mix. The whole linseed ball is then coated with a slow-dissolving coating to provide Osmocotes slow-release technology.
The fertilizer can effectively feed for a whole season with its 6 months of slow release. This product is not suited to large garden trees, but it is very good for trees and shrubs in containers or pots, including indoor plants and ferns, so well deserving of inclusion in our list. This is the second general-purpose fertilizer on our shortlist and it brings a whole load of benefits for those of you looking for convenience and excellent performance for smaller species of trees and shrubs.
How to use: Sprinkle 1 scoop of fertilizer per 4 square feet of planting area and mix or dig into topsoil and water in. Apply once every 6 months. Simple!
Customer Reviews: Amongst the tens of thousands of customer reviews across all major retailers and forums this multi-purpose fertilizer scores an impressive 4.7/5. You can buy this fertilizer online here.
7. Scotts Fertilizer for Trees And Shrubs 11-7-7
- Suitable for a wide range of plants
- Very easy to use, just sprinkle it on the ground
- Strong smell
- No iron
A slow-release evergreen fertilizer that helps trees and shrubs grow well is Scotts Evergreen and Flowering Tree Fertilizer. It has an N-P-K of 11-7-7. We like this product’s easy application, just sprinkle it onto the soil and rake it in. Once the fertilizer is released into the soil, it will continue feeding for up to 2 months.
One minor letdown is the lack of iron which helps prevent the yellowing of leaves. But apart from that, flowering trees, evergreens, acid-loving plants, and flowers will love this fertilizer. In fact, it’s so safe to use that the chances of burning your tree or shrubs are near zero, so long as you follow the directions on the package. Talking of packaging, you can buy this product online and receive it packaged in a practical resealable bag.
How to use: 1 cup per 35 sq feet. Apply every 2 months starting from early spring. The fertilizer can be applied directly from the bag to the soil. Apply evenly and water the plant after application.
Customer Reviews: Thousands of happy customers use Scotts Evergreen and Flowering Tree fertilizer with great results. A really impressive online score of 4.6/5 across all major retail platforms and gardening forums. a re-sealable bag.
8. Miracle-Gro Tree & Shrub Spikes 15-5-10
- Reasonably priced product from a premium brand
- Quick results and easy to apply
- Natural ingredients
- Only suitable for mature trees.
We couldn’t write a shortlist of the best tree fertilizers without including the best-selling Tree and Shrub Food Spikes from Miracle-Gro. This product comes in 12-spike packs and contains only natural ingredients. Each spike is approximately 4″ in length.
You only need to feed your trees evergreens and shrubs once in spring and once in fall using these convenient spikes to see great results. We have used them with great results, there’s no doubt why Miracle-Gro has such a well-established brand name in the industry. A customer-friendly choice Miracle-Gro online here.
How to use: place the enclosed cap on top of the pre-measured solid spike. Insert 2 spikes 2 feet away from the center of the tree’s drip line. Each spike should be at least 3 feet apart. Don’t forget to remove the cap afterward for future use. The spikes should be at least 2 inches below the surface. If the ground is hard use a rubber or wooden mallet to tap the spike into the soil.
Customer Reviews: Over 8,000 users rated this product from Miracle-Gro 4.5/5. Reporting substantial growth after using the spikes. The simple application of this type of product clearly appeals to customers looking for convenience and an easy-to-use product.
Some customers complained of damage to young trees. These spikes are potent and should only be used on mature trees, not in pots or juvenile trees and shrubs.
9. BioAdvanced Shrub and Tree Food 2-1-1
- Unique 2-in-1 insecticide and fertilizer
- Offers 12-month pest control protection
- Not a substitute for a high-quality fertilizer
- Only suitable for mature trees
BioAdvanced Tree and Shrub Protect and Feed is a unique slow-release fertilizer with a blended insecticide. The fertilizer is an N-P-K of 2-1-1, so not the most effective on the list but still worth a mention given its dual function as a pest control formula.
This product will help control whitefly, caterpillars, may beetles and leaf miners, and many more garden pests for up to 12 months with one application. This product is useful for mature trees with less demanding nutritional needs, which are also prone to attack from pests. It’s available to buy on Amazon.com.
How to Use: Available as a granular compound or concentrate. Apply 1/4 cup of concentrate for every 1″ circumference around the tree trunk, or 3/4 cup for every foot of shrub height. Simply sprinkle the granules around the base of the tree or water in the concentrate around the plant’s roots.
How Much Tree Fertilizer to Apply
Different growth stages of trees require varying nutrient requirements. Young trees typically require higher nitrogen levels for rapid growth and development, whereas mature trees need more balanced nutrient inputs to maintain overall health and productivity. Understanding the nutrient needs of trees at various growth stages is critical for optimizing fertilization strategies.
Planting Trees: When planting or transplanting trees, I recommend using around 3 cups of Down to Earth All Natural Tree & Shrub Fertilizer 4-2-4. Mix it in with the soil as you refill the planting hole.
Young or Juvenile trees that are already established apply at a rate of about 1/2 the manufacturer’s dosage as a top dressing. Apply broadly across the crown radius up to 1.5x the crown radium to cover the whole root zone.
It’s important not to over-fertilize young trees as this can lead to excessive growth and damage to roots. Avoid applying fertilizer directly onto the trunk or foliage as this can also cause damage to trees and shrubs.
Existing Mature Trees: Drill holes around 4-6 inches deep around the drip line of the tree (the outer edge of its canopy) at 3 feet intervals. Backfill the holes with slow-release fertilizer or instead hammer in Jobes Tree and Shrubs Fertilizer Spikes 15-3-3 in place of the drills. Both of these methods will avoid rainwater run-off. Alternatively, apply a top dressing of fertilizer across the root zone, equivalent to 1.5x the crown radius, as shown in the diagram below.
How Often to Apply Fertilizer
Usually, a single application of fertilizer in spring and again in late fall is sufficient to support healthy cell development, and offer trees the resilience they need to keep pests and diseases under control.
Fertilizing in Spring
Late April is perhaps the best time to fertilize trees and shrubs. This is when the fertilizer has the best chance to influence new growth, around one month after the fertilizer application in April. Trees and shrubs require feeding before this new growth starts.
Providing this early feed allows the fertilizer to absorb into the soil and be transported through the root system supporting the healthy growth of new shoots as they grow through the spring and summer.
Fertilizing in Fall
Another beneficial time to apply fertilizer is in late fall. Once the temperatures fall to 40 degrees or lower, apply higher concentrations of the fertilizer to help your shrubs resist freezing. Fertilizing during September or October helps trees and shrubs become hardier by giving them staying power through the colder winter months.
Adjusting Schedules Based on Tree Species and Climate
Certain tree species may have unique fertilization requirements or respond better to fertilization at specific times of the year. Research your specific tree species and adjust fertilization schedules accordingly. Similarly, climate plays a significant role in nutrient availability and uptake, so adapt your fertilization practices to local weather patterns.
Application Methods and Techniques
Soil injection is a popular method for applying fertilizer directly into the root zone of trees. The process involves injecting liquid or granular fertilizer into the soil at specific depths and intervals, ensuring efficient nutrient absorption. Soil injection is particularly useful in compacted or heavily landscaped areas, where conventional methods may not be practical.
Broadcasting involves evenly distributing granular fertilizer over the soil surface around the tree. This method is suitable for larger areas with multiple trees or when fertilizing an entire landscape. As rainwater or irrigation percolates through the soil, nutrients are carried down into the root zone.
Deep Root Feeding
Deep root feeding is a technique that delivers nutrients directly to the tree’s root zone by injecting a high-pressure nutrient solution into the soil. This method is ideal for established trees in need of supplemental nutrition and ensures minimal nutrient loss due to runoff or evaporation. If you opt to use fertilizer spikes, you will be simulating the same process as Deep Root Feeding
Foliar feeding involves applying a diluted liquid fertilizer solution directly to the tree’s leaves. This method can provide rapid nutrient uptake and is useful for correcting specific nutrient deficiencies. However, it should not be used as the sole method of fertilization, as it may not address the tree’s complete nutritional needs.
Sustainable and Eco-friendly Fertilization Practices
Excessive fertilization poses risks to the environment, including groundwater contamination and nutrient runoff, which can harm aquatic ecosystems. Employing best management practices, such as soil testing, proper application rates, and eco-friendly fertilizers, helps mitigate these risks.
Strategies for minimizing nutrient runoff and pollution
To minimize nutrient runoff and pollution, consider the following strategies:
- Use slow-release spikes or organic fertilizers to reduce nutrient leaching.
- Time fertilizer applications with tree uptake and avoid fertilizing before heavy rainfall.
- Plant cover crops or use a mulch to prevent soil erosion and nutrient loss.
- Create buffer zones near water bodies to filter runoff and protect aquatic habitats.
Monitoring and Evaluating Fertilization Success
Tracking Growth and Health Indicators
Regularly monitor tree growth and health indicators, such as leaf color, size, and shape, to gauge the success of your fertilization program. Soil tests can also provide valuable information on nutrient availability and help you adjust your fertilization plan as needed.
Adjusting Fertilization Plans as Needed
Based on your monitoring and evaluation efforts, make any necessary adjustments to your fertilization plan. This may include altering the type or amount of fertilizer, adjusting application methods, or modifying the timing of applications to better meet the tree’s needs.
Special Considerations for Fruit and Nut Trees
Unique Nutrient Requirements
Fruit and nut trees have distinct nutrient requirements to support both vegetative growth and fruit production. These trees often require higher levels of potassium, calcium, and boron, as well as careful nitrogen management to avoid excessive vegetative growth at the expense of fruit yield.
Balancing Growth and Fruit Production
Balancing tree growth with fruit production involves carefully managing nitrogen fertilization, pruning, and other cultural practices. Over-fertilization may lead to excessive vegetative growth, reducing fruit yield and quality. Proper pruning encourages a balance between vegetative and reproductive growth, optimizing fruit production.
If you would like to see my recommendation on the best tree fertilizers you can click on the link below to read the full article on each tree and shrub type:
Integrating Fertilization with Overall Tree Care
Coordinating with Pruning and Pest Management
Effective tree care requires an integrated approach, coordinating fertilization with other practices like pruning and pest management. Pruning affects nutrient demands and distribution within the tree, making it crucial to consider pruning activities when developing a fertilization plan. Similarly, proper fertilization can enhance a tree’s ability to resist pests and diseases, reducing the need for chemical interventions.
Developing a Comprehensive Tree Care Plan
A comprehensive tree care plan combines fertilization, pruning, pest management, and other cultural practices to optimize tree health and growth. This holistic approach requires regular monitoring, evaluation, and adjustments to address the changing needs of the tree over its life cycle. Consultation with professional arborists and local extension services can provide valuable guidance in developing and maintaining a comprehensive tree care plan.
RHS – Understanding Soil pH and Testing
University of New Hampshire – Fertilizing Trees and Shrubs
Orogen State University – Spring Is A Good Time To Fertilize Trees