Shrub Fertilizers: When and How (Including The Best Shrub Fertilizers)
Shrub fertilizers are useful for providing vital nutrients to ornamental bushes, evergreen shrubs, and flowering shrubs. Choosing the right fertilizer for shrubs produces lush foliage, beautiful flowers, and shrubs that are more resistant to disease. In addition, the best fertilizers for shrubs are not expensive. Thus, they are ideal for amending poor-quality soil and encouraging healthy growth.
It’s good to remember that adding fertilizer to your garden soil is not always necessary for healthy shrubs. For example, established shrubs growing near lawns or flower beds absorb some of the fertilizer you apply there. In some cases, applying composted manure every three to five years can provide enough minerals for your shrubs.
Additionally, if the soil in your garden already has good levels of nutrients, your shrubs will thrive without additional fertilization. Also, shrubs showing signs of disease or overwatering may not benefit from more nutrients.
In most cases, shrub fertilizers have many benefits. Providing the right amount of fertilizer at the optimal time and in the correct place can result in healthy shrubs in your garden landscape.
Regardless if you grow dwarf shrubs in borders, have large evergreen shrubs as a living fence, or cultivate flowering ornamental shrubs, appropriate fertilization has many benefits.
This article is a complete guide to using shrub fertilizers in your front or backyard. You will also learn about when and how to apply fertilizers to shrubs. At the end of the article, you will find out about the best fertilizers for evergreen and flowering shrubs.
Why You Should Use Shrub Fertilizer
Plant fertilizers contain the essential elements for shrub nutrition. Providing a balanced amount of nutrients helps shrubs grow and thrive. In addition, fertilizing shrubs helps ensure that the plant’s root system is robust and healthy, making them resistant to pests. Also, shrubs that get the proper nutrients bloom throughout the season.
Nutrients in Shrub Fertilizer
The three essential nutrients for shrubs are nitrogen, phosphorus, and potassium. Nitrogen is the vital nutrient that shrubs need for fast growth. Potassium and phosphorus are crucial for flowering shrubs. But shrub fertilizers may also contain micronutrients like calcium, copper, zinc, magnesium, iron, molybdenum, sulfur, and boron.
Before choosing any fertilizer, it’s a good idea to know about the three primary nutrients all shrub fertilizers contain — nitrogen, phosphorus, and potassium. These are usually written as NPK or N-P-K on the fertilizer packaging.
Nitrogen (N)—Nitrogen is the key element for photosynthesis. As the primary component of chlorophyll, nitrogen helps shrubs use the sun’s energy to produce sugars. As a result, nitrogen is vital for growth rate and lush, healthy green leaves.
Phosphorus (P)—This essential shrub nutrient is vital for promoting healthy root and flower growth. Adequate amounts of phosphorus help perennial shrubs develop hardiness. It also stimulates new growth and speeds up maturity.
Potassium (K)—Also called potash, potassium encourages optimal shrub growth. When shrubs have enough potassium, they are more disease resistant and withstand freezing temperatures better. Potassium supports shrub growth from seed until flowering.
The NPK rating refers to the proportion of the three primary nutrients in the fertilizer. So, a shrub fertilizer with an NPK rating of 10-10-10 would be 10 percent nitrogen, 10 percent phosphorus, and 10 percent potassium.
Recommended Evergreen Shrub Fertilizer
Evergreen shrubs tend to require fertilizer that contains more nitrogen than potassium or phosphorus. This is because many evergreen coniferous shrubs have fast growth and require nitrogen to develop lush, green foliage.
Unless you have flowering evergreen shrubs, a fertilizer with an NPK rating of 13-3-4 would be ideal for boxwoods, yews, and spruce shrubs. For flowering evergreen shrubs such as rhododendrons, choose one with an NPK of 11-7-7 to support blooming.
Recommended Flowering Shrub Fertilizer
The best fertilizer for flowering shrubs should have a higher proportion of potassium to phosphorus and nitrogen. This is because blooming takes a lot of energy from the shrub.
Therefore, a suitable flowering shrub fertilizer would have an NPK rating of 8-4-12. However, in soil with nitrogen deficiencies, a fertilizer with an NPK rating of 18-6-12 would be a better choice.
Shrub Fertilizer vs. Shrub Food
Shrub fertilizer is not food for shrubs. People often refer to fertilizing shrubs as feeding them. Even some fertilizer brands have the name “plant food” in the title. However, all shrubs and plants create their own food through photosynthesis. Fertilizer is only minerals and nutrients that the soil lacks to promote healthy growth and photosynthesis.
Minerals in the soil such as nitrogen (N), phosphorus (P), and potassium (K) are necessary for plants to produce food. Additionally, micronutrients are also essential to ensure lush foliage and colorful blooms.
How to Decide If Your Shrubs Need Fertilizer
Shrub fertilization is necessary if plants lack nutrients. To decide if you need to fertilize shrubs, it’s best to check the soil for nutrient deficiencies. Also, a slow growth rate, smaller than normal leaves, poor blooming, and stunted growth are signs you need to fertilize shrubs.
As a rule, if shrubs appear healthy, growing at the proper rate, and flower as you expect, you may not need to apply fertilizer. Established shrubs growing in soil that contains decomposing organic matter will thrive without fertilization.
Here are some handy tips on how to improve soil quality so that your shrubs grow better:
Soil test to decide if shrub fertilization is necessary. Before ordering shrub fertilizer online or driving to your local garden center, do a soil test. A soil test will tell you the soil’s pH levels and if there is a nutrient deficiency. If any of the three primary nutrients are lacking, you can buy the appropriate type of shrub fertilizer.
Growth rate helps decide if you need to use fertilizers. For example, is your shrub growing slower than it should? Or have you noticed that new leaves are smaller and appear less frequently? Or maybe leaves drop early in fall before turning color? These signs could indicate that you need to address nutrient deficiencies in the soil with an appropriate shrub fertilizer.
It’s a good idea to remember that pest infestations, disease, overwatering, or compacted soil can all cause growth issues. If external stressors are affecting shrub growth, you’ll have to address those first before fertilizing the ground.
When was the shrub planted? Newly planted shrubs don’t need fertilizing until they establish a robust root system. If you apply fast-release fertilizer at planting, you may inhibit growth rather than speed it up. Usually, at planting, it’s enough to work in decomposing organic matter to the ground to provide the necessary nutrients.
Where are the shrubs growing? If shrubs are growing in a flower bed or beside lawns that you regularly fertilize, you don’t need to apply fertilizer. This is because shrub roots absorb nutrients from other plant fertilizers. But if shrubs are growing in loamy soil, lacking organic matter – additional fertilization can promote healthy growth.
Common Types of Shrub Fertilizers
The two types of fertilizers for shrubs are slow-release shrub fertilizers and fast-release fertilizers.
Slow-release fertilizers dissolve over months to gradually release nutrients in the ground where shrubs are growing. Typically, slow-release fertilizers are easier to apply. They are also more suited to recently planted shrubs.
Fast release fertilizers are also called water-soluble fertilizers. They have the advantage of being cheaper, but they are trickier to apply. They may quickly run through sandy soil without benefiting the shrub’s roots.
Slow-Release Shrub Fertilizer vs. Fast-Release Shrub Fertilizer
Slow-release fertilizers are typically better for shrubs. The advantage over fast-release fertilizers is that nitrogen gets released at a uniform rate. This results in better growth throughout the season. Also, because they release nutrients slower, there is less risk of nutrient runoff and contaminating the environment.
Typically, fast-release shrub fertilizers are ideal for a quick fix. For example, suppose an ornamental shrub has yellowing foliage or showing signs of stress. In that case, prompt treatment with a water-soluble fertilizer blend may restore health fast. Or, say you have a newly planted shrub and you want to boost fast growth. Then, a fast-release application could do the trick and cause a quick growth spurt.
Natural Shrub Fertilizer
Natural shrub fertilizers release their nutrients slowly. They are usually composed of decaying organic matter. Examples of natural fertilizers are aged cow or horse manure, composted vegetation, sewage sludge, blood meal, or bone meal. There are also commercially-produced natural shrub fertilizers you can buy.
Using natural fertilizers for healthy shrub growth has advantages. First, natural fertilizers are suitable for organic gardening and don’t contain potentially harmful chemicals. Second, they have a balanced mineral content and help improve soil structure. Additionally, the lack of synthetic chemicals means there is less risk of root burning.
It’s good to note that natural fertilizers for shrubs have some disadvantages. For example, the nitrogen content is usually lower than synthetic slow-release fertilizer. This means you need to apply more organic matter and more frequently. However, for many gardeners, the advantages of natural fertilizers outweigh any seeming disadvantages.
How Much Shrub Fertilizer to Apply
The amount of fertilizer to use on a shrub depends on its root area and nitrogen content. Typically, younger shrubs need more nitrogen than mature plants because they grow faster. Most shrubs can take between two and four pounds (0.9 – 1.8 kg) of actual nitrogen per 1,000 square feet (93 square meters) of root spread a year.
To apply the right amount of fertilizer, follow the manufacturer’s instructions on mixing the liquid (fast-release) or spreading the granules (slow-release). You also need to calculate the diameter of your shrub’s root spread. This is typically one and a half times the area of the crown.
For example, if the shrub’s foliage has a spread of 3 ft. (1 m), the root zone will be 4.5 ft. (1.4 m) around the central stem. This area is 1.5 times the shrub’s foliage spread.
How to Fertilize Shrubs
You can fertilize shrubs indirectly or directly. Indirect fertilization is when shrubs are fertilized when you provide nutrients to lawns or flower beds. The best way to fertilize shrubs is by the direct fertilization method.
Use a drop-type spreader to disperse the appropriate amount of fertilizer. The best way to do this is to divide the fertilizer amount in half. Then cover the root zone by applying in one direction. Then apply the other half in a perpendicular direction. After applying the granules, make sure that no fertilizer is left on the leaves.
How Much Shrub Fertilizer to Use – Example
The right amount of fertilizer to use depends on the soil condition and the size of the shrub. When fertilizing shrubs, it’s crucial to apply a precise amount of fertilizer. Too much fertilizer can result in root burn and damage foliage. Generally, it’s best to err on the side of caution and apply too little rather than too much.
Here is a simple way to determine how much shrub fertilizer to use.
Recommended amounts of fertilizer are in pounds per 1,000 square feet (lbs. per sq. ft.) of the root area. To calculate the square footage of the root zone, you need to use Pi (π or 3.14). Here is the simple calculation:
- Divide the diameter of the shrub’s spread by 2 to get the radius
- Square the number (multiply the result by itself)
- Multiply the result by 3.14 (π)
Here’s an example of working out the amount of fertilizer required for a dwarf shrub that has a spread of 3 ft.
- 3 ÷ 2 = 1.5
- 1.5 x 1.5 = 2.25
- 2.25 x 3.14 (π) = 7.06 sq. ft.
The amount of fertilizer to apply depends on the proportion of nitrogen in the fertilizer. For example, a 10 lbs. bag of 13-3-4 contains 13 percent nitrogen. Thirteen percent of 10 lbs. is 1.3 lbs. Therefore, the whole pack contains 1.3 actual pounds of nitrogen.
The recommendation is to apply 2 – 4 pounds of actual nitrogen per 1,000 sq. ft. So for the shrub with a 4-foot spread in the example, you need to apply 0.014 – 0.028 pounds of nitrogen (7 sq. ft. is 1/142 of 1000 sq. ft. – so you will need to divide the original recommendation by 142).
When to Apply Shrub Fertilizer (The Ideal Time to Apply Shrub Fertilizer)
The best time to fertilize shrubs is either just before or just after the growing season. This means that spring or fall are ideal times to boost nutrient levels in the soil. Spring fertilization gives shrubs a boost before vigorous growth. Fall fertilization helps develop strong roots for cold-hardiness.
Fertilizing Shrubs in Spring: Applying fertilizer in early spring helps shrubs thrive after the dormant winter period. Spring fertilization also helps shrubs resist pests and diseases that become more prevalent in late spring and early summer.
Fertilizing Shrubs in Fall: Some gardeners apply fertilizer to shrubs in the fall to strengthen plants before winter.
Should You Fertilize Newly Planted Shrubs?
Generally, it would be best if you didn’t fertilize shrubs that are newly planted. This is because shrubs take a few months to establish a robust root system. Until this time, they won’t absorb nutrients. In addition, some studies suggest that high nitrogen content can surpass root growth rather than benefit it.
The Best Shrub Fertilizers
Let’s look at some of the best fertilizers for shrubs. For each of these fertilizers, you can read the pros and cons of each one to help you pick the best one for your ornamental or evergreen shrubs.
Miracle-Gro Shake’ N Feed for Flowering Shrubs
If you have flowering shrubs, then Miracle-Gro Shake ‘n Feed is an excellent choice. The natural ingredients contain worm castings, kelp, bone meal, and feather meal to provide soil nutrients. The high nitrogen content and high potassium levels are ideal for lush green foliage and healthy blooms. This natural shrub fertilizer has an NPK rating of 12-4-8.
Pros:
- It contains an ideal balance of nitrogen and potassium
- Easy to use
- Contains organic fertilizers
- No mixing required
- Ideal for acid-loving flowering shrubs and trees
Cons:
- Large bushes with masses of flowers may require extra fertilizer to support blooming
This fertilizer is available on Amazon.
Scotts Continuous Release Evergreen Flowering Shrub Fertilizer
Scotts Continuous Release fertilizer is designed to promote healthy evergreen growth. The high nitrogen proportion to potassium and phosphorus ensures lush foliage and vigorous root growth. The shrub fertilizer is easy to use, and there is no mixing necessary. An advantage of this fertilizer is that it releases nutrients for up to two months.
This fertilizer is suitable for evergreen shrubs, as well as rhododendrons, hydrangeas, dogwoods, magnolias, and camellias. It has an NPK rating of 11-7-7.
Pros:
- Ideal for evergreen and flowering shrubs
- Easy to use
- Value for money
- Encourages fast growth
- Added sulfur for acid-loving shrubs
Cons:
- Low iron content
- Lower NPK than other similar fertilizers
- Pungent smell
This fertilizer is available on Amazon.
Miracle-Gro Tree & Shrub Plant Food Spikes
One of the best fertilizers for shrubs is the “plant food” spikes by Miracle-Gro. To apply the fertilizer in spring, you just need to drive the required number of spikes into the ground. The slow-release shrub fertilizer will maintain the soil nutrient level throughout the growing season. It has an NPK rating of 15-5-10.
A benefit of these soil nutrient spikes is that they contain organic ingredients. It is also easy to measure the amount of fertilizer you require without complicated calculations.
Pros:
- Promote lush foliage and vibrant green colors
- It only contains natural ingredients
- Easy to use
- Excellent value for money
Cons:
- Not suitable for newly growing shrubs or juvenile trees
This fertilizer is available on Amazon.
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