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What fertiliser is best for shrubs?

A quick look on Mitre 10’s fertiliser section on their website shows a mere 217 options to choose from. Mind-blowing! While the range of fertilisers available today is outstanding, it can also be confusing knowing which ones to choose.


In this article, you will learn about the different types of fertiliser for different applications.


Before you get too worried, the bulk of ornamental plants for the home garden are all happy with a general purpose fertiliser. But just in case you (like me) got the wrong bag off the shelf, or didn’t read the label properly, here’s some handy things to know about fert. Furthermore, we’ll group them into synthetic and organic so if you’re particularly passionate one way or another, you can skip straight to the ones you like.


Organic


General Blood & Bone

Blood and bone fertiliser is a type of organic fertiliser made from dried blood and ground bone meal. It has its own set of advantages and disadvantages. Here are two pros and two cons of using blood and bone fertiliser:


Pros:

  1. Slow-Release Nutrients: Blood and bone fertiliser provides a slow and steady release of nutrients to plants. This slow-release feature helps prevent nutrient leaching and reduces the risk of nutrient runoff, making it an environmentally friendly choice. Plants can access nutrients over an extended period, promoting steady growth and reducing the need for frequent reapplication.

  2. Organic and Natural: Blood and bone fertiliser is an organic and natural product, which appeals to gardeners and farmers who prefer to avoid synthetic chemicals. It enriches the soil with organic matter and essential nutrients, improving soil structure and fertility over time. It can also enhance microbial activity in the soil.


Cons:

  1. Odour: One significant drawback of blood and bone fertiliser is its strong and unpleasant odour, primarily due to the blood content. This odour can be offensive to some people, making it less desirable for use in urban or residential areas. It's essential to store and apply the fertiliser in a well-ventilated area and take precautions to minimize exposure to the smell.

  2. Slow Acting: While the slow-release nature of blood and bone fertiliser is an advantage, it can also be a drawback in some situations. If you need rapid results or have plants with specific nutrient deficiencies, this fertiliser may not provide a quick solution. In such cases, fast-acting synthetic fertilisers or other organic fertilisers with higher nutrient concentrations may be more appropriate.


In summary, blood and bone fertiliser has the advantages of slow-release nutrients and being organic and natural, but it comes with the disadvantages of a strong odour and a relatively slow action compared to synthetic alternatives.


Price you can expect to pay: around $17-20 for a 3kg bag.


Horse manure

Nothing quite like it, but try and get stuff you know has been sitting around for a while, or stockpile some bags yourself and let them break down for a few months before using, otherwise you’ll burn the roots of your plants from the high levels of nitrogen, and more importantly it needs time to compost properly and kill the weed seeds in it. (Note: cow manure is naturally composted and can be a better option if available, likewise chicken manure).


Pros:

  1. Nutrient-Rich: Horse manure is a nutrient-rich organic fertiliser that can enhance soil fertility. It contains essential nutrients like nitrogen, phosphorus, and potassium, which are vital for plant growth. These nutrients can promote healthy plant development and improve crop yields when used properly.

  2. Organic and Sustainable: Horse manure is an organic fertiliser, which means it doesn't contain synthetic chemicals or additives that can harm the environment or soil health. Using horse manure can be a sustainable way to recycle animal waste and reduce the need for chemical fertilisers, contributing to more environmentally friendly farming practices.


Cons:

  1. Weed Seeds and Pathogens: Horse manure may contain weed seeds and pathogens that can be detrimental to your garden or crops. If the manure isn't properly composted or treated (as mentioned above), it can introduce weeds and disease-causing microorganisms to your soil, leading to weed infestations and potential plant diseases.

  2. Imbalanced Nutrient Ratios: While horse manure is nutrient-rich, its nutrient ratios may not always match the requirements of specific plants or crops. It typically has a high nitrogen content but can be relatively low in phosphorus and potassium. This imbalance can lead to nutrient deficiencies or excesses, affecting plant health and growth. It's important to test your soil and adjust your fertiliser application accordingly.


To mitigate the disadvantages of using horse manure, it's crucial to compost it properly to kill weed seeds and pathogens and to ensure a more balanced nutrient profile. Additionally, consider using it in conjunction with other organic or synthetic fertilisers to provide a well-rounded nutrient supply for your plants.


Price you can expect to pay: Drive past the gate ways of local horse establishments, generally you can pick up 20kg bags for anything from $1-$5 per bag.



Seaweed Fertiliser

Organic seaweed fertiliser, derived from various types of seaweed or algae, has gained popularity in gardening and agriculture due to its natural composition and potential benefits. Here are two pros and two cons of using organic seaweed fertiliser:


Pros:

  1. Nutrient-Rich: Organic seaweed fertiliser is a rich source of essential nutrients such as nitrogen, potassium, phosphorus, and various trace elements. These nutrients are readily available to plants, promoting healthy growth and improving overall plant vigour. Additionally, seaweed contains growth-promoting hormones like auxins, cytokinin, and gibberellins, which can enhance root development and flowering.

  2. Enhanced Soil Health: Seaweed fertilisers can improve soil structure and microbial activity. They contain organic matter that helps to increase soil water retention, aeration, and nutrient-holding capacity. The organic material in seaweed can also encourage beneficial microorganisms in the soil, leading to better nutrient cycling and a healthier soil ecosystem.


Cons:

  1. Cost: Organic seaweed fertiliser can be more expensive compared to synthetic or traditional fertilisers. The harvesting, processing, and transportation of seaweed can be labour-intensive and costly, which may make it less budget-friendly for some gardeners or farmers. In saying that, it is often sold in a concentrate and typically a little goes a long way.

  2. Variable Composition: The nutrient content of seaweed fertiliser can vary depending on the type of seaweed used, its source, and the processing methods. This variability can make it challenging to precisely control the nutrient levels in your soil, which may be a disadvantage when compared to synthetic fertilisers with consistent nutrient profiles.


Overall, organic seaweed fertiliser can be a valuable addition to your gardening or farming practices due to its natural nutrient content and soil-enhancing properties. However, its cost and variability in nutrient composition should be considered when deciding whether to use it in your specific growing environment.


Price you can expect to pay: $16-20 for 2.5L


Synthetic


General NPK

Nitrogen-Phosphorous-Potassium fertiliser is one of the most common ones you’ll come across, albeit with several different labels. You can use this on virtually any shrub or ornamental tree.


Pros:

  1. Nutrient Enhancement: NPK fertilisers provide essential macronutrients (nitrogen, phosphorus, and potassium) that are crucial for plant growth. These nutrients promote healthy foliage (nitrogen), strong root development (phosphorus), and overall plant vigour (potassium). Using NPK fertilisers can help improve crop yields and quality.

  2. Convenience and Control: NPK fertilisers are available in various formulations, making it easy for farmers and gardeners to choose a product that suits their specific crop and soil needs. This allows for better control over nutrient application and simplifies the process of providing plants with the necessary nutrients.


Cons:

  1. Environmental Concerns: One significant drawback of NPK fertilisers is their potential to cause environmental problems. When not managed correctly, excess nutrients from fertilisers can leach into groundwater or runoff into nearby water bodies. This can lead to water pollution, algal blooms, and other ecological issues, harming aquatic ecosystems and human health.

  2. Nutrient Imbalance: While NPK fertilisers provide the three essential macronutrients, they may not address all of a plant's nutrient requirements. Overreliance on NPK fertilisers without considering secondary and micronutrients can lead to nutrient imbalances in the soil, potentially reducing plant health and productivity over time. It's important to conduct soil tests and consider a broader range of nutrients for optimal plant nutrition.


In summary, NPK fertilizers offer nutrient enhancement and convenient control over nutrient application, but they also come with potential environmental risks and the risk of nutrient imbalances if not used judiciously. Proper application and monitoring are essential to maximize the benefits of NPK fertilisers while minimizing their drawbacks.


Price you can expect to pay: $26-30 for 5kg


Specialised Fertilisers


Fruit/citrus tree mix


Fruit and citrus tree specialised fertilisers are recommended for several important reasons:


1. Nutrient Balance: Fruit and citrus trees have specific nutrient requirements that differ from other types of plants. They need a balanced supply of essential nutrients to support healthy growth, fruit production, and disease resistance. Specialised fertilisers are formulated to provide the right proportions of nutrients that these trees need, such as nitrogen (N), phosphorus (P), potassium (K), and micronutrients like iron, zinc, and magnesium.


2. Increased Fruit Production: Fruit trees have higher nutrient demands than many other plants, especially during the growing season and fruit-bearing periods. Specialised fertilisers are designed to promote flowering, fruit set, and fruit development, resulting in increased fruit production and improved fruit quality.


3. pH Adjustment: Citrus trees, in particular, prefer slightly acidic to neutral soil pH levels. Specialised fertilisers may contain pH-adjusting components to help maintain the ideal pH range in the soil, ensuring that nutrients are readily available to the trees.


4. Micronutrient Support: Fruit and citrus trees can be susceptible to micronutrient deficiencies, such as iron chlorosis. Specialised fertilisers often include micronutrients like iron, manganese, and zinc in forms that are more readily absorbed by the plants, preventing deficiencies and associated problems.


5. Controlled Release: Some fruit tree fertilisers are formulated for slow or controlled-release of nutrients. This can provide a steady supply of nutrients to the trees over an extended period, reducing the risk of nutrient imbalances or excessive growth spurts.


6. Disease Resistance: Proper nutrition from specialised fertilisers can enhance the overall health and vigour of fruit and citrus trees. Healthy trees are better able to resist diseases and pests, reducing the need for chemical treatments.


7. Avoiding Excessive Growth: Using a general-purpose fertiliser with a high nitrogen content can lead to excessive vegetative growth at the expense of fruit production. Specialised fruit and citrus fertilisers are often formulated with a balanced NPK ratio to encourage both growth and fruiting.


8. Nutrient Uptake Efficiency: These fertilisers are designed to improve nutrient uptake efficiency by fruit trees, ensuring that the applied nutrients are absorbed and utilised effectively, minimizing waste and environmental impact.


9. Targeted Formulations: Specialised fruit and citrus fertilisers are often tailored to the specific needs of different types of fruit trees, such as apple, pear, orange, lemon, etc., taking into account their individual nutrient requirements.


Using these fertilisers can result in healthier, more productive fruit trees and better-quality fruit. However, it is critical that these are applied at the right time (typically once a year in spring) otherwise it will be ineffective.


Price you can expect to pay: $26 - $30 for 5kg


Rose fert


Roses are unique plants that have specific nutritional needs, and using a fertiliser tailored to these needs can help promote healthy growth, abundant flowering, and disease resistance. Here are some key reasons why specialised fertilisers are recommended for roses:


1. Balanced Nutrient Ratios: Roses require a balanced supply of essential nutrients to thrive. Specialised rose fertilisers are formulated to provide the right ratios of nitrogen (N), phosphorus (P), and potassium (K), as well as secondary and micronutrients like magnesium, sulphur, iron, and manganese. These balanced ratios support overall plant health and promote strong root development, vibrant foliage, and abundant blooms.


2. Increased Flower Production: Roses are prized for their beautiful flowers, and specialised rose fertilisers typically contain higher levels of phosphorus (the second number in the N-P-K ratio) to encourage prolific flowering. Phosphorus is essential for flower bud formation and development, and a higher phosphorus content in rose fertilisers helps ensure a profusion of blossoms.


3. Disease Resistance: Roses can be susceptible to various diseases, and a well-balanced, specialised fertiliser can help improve the plant's resistance to common rose ailments. Proper nutrition strengthens the plant's immune system, making it less susceptible to diseases and pests.


4. Soil pH Adjustment: Some rose fertilisers are formulated with ingredients that can help adjust soil pH. Roses generally prefer slightly acidic to neutral soil (pH around 6.0 to 7.0). Specialised fertilisers may contain elements like sulphur to lower pH or lime to raise it, ensuring the soil pH is within the optimal range for rose growth.


5. Slow-Release Formulas: Many specialised rose fertilisers come in slow-release formulations. These slowly release nutrients over an extended period, providing a consistent and steady supply of nutrients to the roses. This gradual nutrient release minimizes the risk of over-fertilisation and nutrient runoff, which can harm the environment.


6. Targeted Micronutrients: Roses often benefit from specific micronutrients, such as iron and magnesium, to maintain healthy foliage and flower colour. Specialised rose fertilisers may include these micronutrients to address any deficiencies that may occur in the soil.


7. Customised Formulations: Some specialised rose fertilisers are formulated for specific rose types, such as hybrid tea roses or floribunda roses. These formulations take into account the unique needs of different rose varieties, optimizing their growth and flowering.


Price you can expect to pay: $26-30 for 5kg


Acid Fert


Specialised fertiliser mixes are recommended for acid-loving plants because these plants have specific nutritional requirements and thrive in acidic soil conditions. Here are several reasons why specialised fertilisers are beneficial for acid-loving plants:


1. pH Requirements: Acid-loving plants, such as azaleas, rhododendrons, blueberries, and camellias, prefer soil with a pH level below 7.0, which indicates acidic conditions. Specialised fertilisers for acid-loving plants are formulated to help maintain or lower the soil pH, creating an environment in which these plants can thrive.


2. Nutrient Availability: Soil pH significantly influences nutrient availability to plants. In acidic soils, certain essential nutrients like iron, manganese, and aluminium become more accessible to acid-loving plants. Specialised fertilisers are designed to provide these specific nutrients in forms that are readily absorbed by the plants, ensuring they receive the nutrients they need.


3. Micronutrient Balance: Acid-loving plants often require higher levels of certain micronutrients, such as iron and manganese, which can become deficient in alkaline soils. Specialised fertilisers are formulated to contain these micronutrients in balanced amounts to prevent deficiencies and promote healthy growth.


4. Slow Release Formulations: Many specialised fertilisers for acid-loving plants come in slow-release formulations. This slow-release feature ensures a steady supply of nutrients over an extended period, reducing the risk of nutrient leaching and providing consistent nutrition to the plants.


5. Organic Matter: Acid-loving plants typically grow in woodland or forested environments with rich organic matter in the soil. Specialised fertilisers for these plants may include organic components that enhance soil structure, improve water retention, and encourage beneficial microorganisms, mimicking the natural conditions in which these plants thrive.


6. Specific Nutrient Ratios: Acid-loving plants may have unique nutrient ratio requirements. Specialized fertilisers take these ratios into account, providing the right balance of nutrients to support optimal growth and flowering.


7. Reduced Risk of Alkaline pH: Using general-purpose fertilisers with high pH can gradually raise the soil pH over time, making it less suitable for acid-loving plants. Specialised fertilisers help maintain the acidic pH necessary for these plants by minimizing the risk of alkaline soil conditions.


In summary, specialised fertilisers for acid-loving plants are tailored to meet the specific nutritional needs and pH preferences of these plants. Using such fertilisers ensures that acid-loving plants receive the right nutrients in forms they can readily absorb, promoting healthy growth, vibrant foliage, and beautiful blooms in acidic soil conditions. Once again, they need to be added at the right time of year (typically spring) otherwise the plants won’t be able to take advantage of them.


Price you can expect to pay: $26-30 for 5kg


General tips for applying fertiliser


1. Never overdose. Use the manufacturer’s guidelines on the bag, overdosing can do harm to the plant. It’s like the stomach pain we get when we overeat innit?


2. Apply around the circumference of the foliage. This is because for most plants the outermost and hungriest roots will be out there, ready to pick up and distribute any new food back up the plant.


3. Before applying any fertiliser, conduct a soil test to determine its nutrient content and pH level. This will help you choose the right type and amount of fertilizer. Soil testing kits are inexpensive and can be purchased from garden centres, however make sure you follow the instructions to the letter to get an accurate result.


4. Always read and follow the instructions on the fertiliser packaging. This includes recommended application rates, timing, and any safety precautions.


5. Apply fertiliser at the right time, typically during the growing season. Different plants have varying nutrient requirements, so research the ideal timing for your specific plants.


6. Apply fertiliser evenly to prevent over-fertilisation in some areas and under-fertilisation in others. You can use a spreader for large areas or a handheld spreader for smaller ones.


7. Water your garden before applying fertiliser to ensure the soil is moist but not waterlogged. After applying fertiliser, water again to help dissolve and distribute the nutrients into the root zone.


8. If you're using concentrated fertilisers, such as liquid or granular forms, dilute them according to package instructions to avoid damaging plants.


9. Applying a layer of organic mulch (e.g., straw or wood chips) after fertilising can help conserve moisture, regulate soil temperature, and prevent nutrient loss due to runoff.


10. Maintain a gardening journal to record when and how much fertiliser you applied. This can help you track the effectiveness of your fertilisation practices and make adjustments as needed.


Remember that each garden is unique, and the specific fertiliser application requirements may vary based on your location, soil type, and the plants you're growing. Regular monitoring and adjusting your fertilisation strategy as needed will help you maintain a healthy and productive garden.

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