Deep Root Fertilization

Deep root feeding or fertilization is often a controversial topic in the arboriculture field. Some experts believe it helps tree roots and allows them to thrive. Meanwhile, others think it can be detrimental to the health of a tree.

Knowing the benefits and method of deep root fertilization is essential in helping you determine if your tree needs it. It also helps to understand how deep root fertilization treatment differs from regular fertilization.



Below, we discuss deep root fertilization in detail. We also dispel some myths surrounding deep root tree fertilization to clear your doubts.

Deep root fertilization is a fertilization technique in which nutrients are applied directly to the root zone of trees and shrubs. In this process, you inject a deep root fertilizer into the soil at a depth of 8 to 12 inches.

Sometimes, you may have to inject the deep root fertilizer a bit deeper, depending on the soil conditions and the species. The main aim of deep root feeding is to provide nutrients to the plant.

These nutrients include:

• Nitrogen
• Phosphorus
• Potassium

Applying these directly to the root system can help improve the plant's vigor and overall health. The technique also helps improve the soil's structure. It enhances the water retention capabilities of the soil, promoting root growth.

It's best to perform trees deep root fertilization once or twice every year. The age of the tree and the soil condition will determine how often deep rooting feeding is required.

Soil amendments are organic materials added to the soil to improve its structure. They help improve the water retention and nutrient-holding capacity of the soil.

Some common soil amendments used in deep root fertilization include the following:

• Compost
• Humic Acid
• Mychorrhizal Fungi

Compost

Compost is made using decomposed organic matter, including food scraps, grass clippings, and leaves. You can also add yard and garden waste to compost.

In composting, soil bacteria and fungi break down organic matter over time. The result is a nutrient-rich soil amendment. It helps do the following:

• Improve Soil Structure: Compost increases the soil's ability to hold nutrients and water. It also reduces soil impaction and promotes the spread of beneficial microbes.
• Increases Nutrient Availability: Compost contains essential nutrients like potassium, calcium, magnesium, and nitrogen. It maintains healthy soil, which is necessary for proper tree growth.
• Reduces Soil Erosion: Since compost stabilizes the root system, it prevents soil erosion. That further helps the ecosystem by reducing soil’s surface run-off.
• Natural Pest Control: The beneficial microbe growth resulting from compost helps control harmful pests. So, compost can reduce the use of chemical pesticides in preventing plant disease.

Humic Acid

Humic acid is an organic acid found in peat, natural environments, and soil. It results from the decomposition of organic matter over extended periods.

The acid has plenty of beneficial properties. It can improve soil fertility and promote microbial activity. When used for fertilizing trees, it has the following benefits:

• Improves Nutrient Uptake: Humic acid breaks down organic matter in the soil. That makes nutrients readily available for tree roots to uptake.
• Enhances Root Development: Humic acid also promotes root growth. Trees can withstand harsh weather conditions and stress with a stronger root system.
• Offers Resistance: Some research shows that humic acid makes a tree resistant to pests and diseases.
• Improves Water Retention: Humic acid lowers the need for irrigation and watering by improving water retention. It can be a good soil amendment for environments that experience periods of drought.

Humic acid comes in two forms; granular fertilizer and liquid concentrates. Opt for liquid concentrate for faster absorption. Granular formulations are better for improving soil structure.

Mychorrhizal Fungi

Mycorrhizal fungi form a mutualistic relationship with the plant's roots. The fungi attach themselves to the root system and extend their reach into the soil.

The relationship between the plant and the fungi is symbiotic. It means both organisms benefit from this relationship. Here's how:

• The fungi get nutrients and sugars from the plant.
• The plant gets increased access to soil nutrients.

You should add Mycorrhizal fungi for deep root feeding if you're growing plants in stressful conditions. The fungi also help plants thrive in sought periods.

There are two types of Mycorrhizal fungi to use in deep root fertilization treatments:

• Endomycorrhizal Fungi: These fungi penetrate plant roots. They form arbuscules, structures that help plants uptake minerals and water. Some examples of these fungi include Glomus intraradices, Rhizophagus irregulars, and Gigaspora margarita. 
• Ectomycorrhizal Fungi: These fungi form a sheath around tree roots. These fungi's mycelium (roots) extend into the soil and develop a network of filaments. These filaments extract water and nutrients from the area. Ectomycorrhizal fungi form symbiotic relationships with fir, spruce, pine, and birch. Most of these fungi are from Laccaria, Boletus, and Amanita genera.

Unlike surface fertilization, the deep root fertilization process requires special equipment. Here's what a professional will use:

• Soil Prober/Auger: The auger helps you create holes in the soil. These holes will provide the entryway for fertilizers.
• Injection Equipment: The injection equipment is used to squirt fertilizer into the soil through the holes.
• Fertilizer: The professional arborist will determine which fertilizer will be most suitable for your plant. Most trees only require fertilizers containing the three essential nutrients. But others may require trace amounts of micronutrients.
• PPE: Arborists also wear personal protective equipment to protect themselves from fertilizer exposure. These include safety glasses and gloves.
• Watering Equipment: The arborist will also use watering equipment, such as a hose, to water the area following fertilization. It will allow the tree's absorbing roots to take up the fertilizer mixed in water.

In some cases, a soil test may be necessary to determine what type of fertilizer to use and how much. Following the soil test, the arborist will make holes near the tree roots.



They will then inject the fertilizer and water the area. Maintenance involves checking the soil temperature and moisture levels regularly.

The frequency of deep root feeding depends on the following factors.

• Type of Plant: Some trees, such as pines and firs, need deep root feeding more often than others. Plants with high nutritional needs require more frequent deep root feeding.
• Soil Compaction: The higher the soil compaction, the harder it is for the plants to uptake nutrients. So, compacted soils require deep root fertilization more often.
• Conditions: Plants under stress conditions or harsh weather also need frequent deep root feeding.

However, you should consult a horticulturist or arborist to find the right frequency of fertilization. Over-fertilization can result in problems like waterway pollution and root burn.

Here are a few myths about deep root fertilization and the truth around them:

• DIY Deep Root Fertilization
• All Trees Need It

DIY Deep Root Fertilization

Not really. You won't have the specialized equipment needed for this fertilization method. Even if you have the equipment, you might not know how to apply the fertilizer.

For example, you may not be able to find the tree fibrous roots. You may not know what rate to apply the fertilizer. If you haven't performed a soil test, you won't even know which type of fertilizer to use.



So, it's best to leave this task to professionals.

All Trees Need It

Trees growing in natural forest floors don't need deep root feeding. There's enough organic matter on the forest floor to provide natural nutrients to the plant.



Deep root fertilization is more beneficial for trees in urban settings. The fertilization method can supplement the plant with natural nutrients, mimicking the natural environment of trees in manicured lawns.

Differences Between Deep Root and Regular Fertilization

There are a few differences between regular and deep root fertilization:

Application Method

In regular fertilizer, you apply fertilizer on the soil's surface. The fertilizer dissolves into the ground slowly over time. Then, the roots absorb this fertilizer and send it through the plant's vascular system.

In deep root feeding, fertilizer is applied to the root systems rather than the soil surface. That facilitates quick uptake.

Depth of Application

The fertilizer is applied a few inches into the soil in deep root systems. But in regular fertilization, there's no depth of application. The fertilizer stays on the surface.

Nutrient Delivery

Regular fertilization is a less targeted approach than deep root feeding. The former often results in nutrient loss through runoff and evaporation.

But deep root fertilization allows even and well-distributed nutrient delivery. It also reduces the risk of leaching or surface runoff.

Frequency

The frequency of both types of fertilization is the same. But in some cases, deep root fertilization is applied somewhat more frequently than regular fertilizer.

How often you apply fertilizer will depend on soil structure, soil compaction, weather conditions, and plant type.

Potential for Damage

Regular fertilization has more potential for plant damage than feeding tree roots. Incorrect or excessive regular fertilization can stunt root growth. It may also cause leaf burn, plant stress, and even death.

When you fertilize trees via deep root feeding, you only target the tree feeder roots. So, other parts of the plant are not impacted.

Cost

Deep root fertilization is more expensive since you have to reach the root systems. That requires specialized equipment and professional intervention.

You may also have to add soil amendments to the root zone, increasing the cost. But regular fertilization is cheaper.

You do not need specialized equipment. If you have some basic DIY gardening skills and a few tools, you can do it yourself.

Timing

There's a specific timing for deep root fertilization, preferably during spring or fall. During this time, the soil is moist, and the tree's roots experience no stress. It's also the time when plants are growing actively. So they can absorb all the nutrients readily.

Meanwhile, you can perform regular fertilization at any time. Still, it's best to avoid fertilizing trees during droughts and heat waves. Fertilizing trees during harsh weather conditions may result in severe root damage.

Environmental Impact

Regular fertilization is less eco-friendly than deep root feeding. In regular fertilization, you apply the powder or liquid fertilizer to the top of the soil. The liquid fertilizer may evaporate in hot conditions. Similarly, the liquid of powder may leach into the groundwater or runoff.

Deep root fertilization reduces nutrient loss and environmental impacts. The fertilizer goes directly to the root zone instead.

Health Benefits

Both types of fertilization methods have similar benefits. But fertilizing trees at the root zone may be more effective at improving plant health.

Regular fertilization can also promote growth. But it may be less effective since it is not targeted. It may also not have long-term benefits.

Composition

A deep root tree fertilizer typically has slow-release nitrogen, phosphorus, and potassium. The slow-release nitrogen goes into the soil over time.

But a regular fertilizer may have fast-acting nutrients. These fertilizers dissolve quickly and provide instant nutrients to the soil.

Fertilizer Type

Most deep root fertilizers use organic materials from natural sources, such as compost, blood meal, and bone meal. These fertilizers are ideal for landscape trees and turf grass. They often also contain micronutrients.

Regular fertilizers can be synthetic or organic. Synthetic fertilizers are manufactured chemically. They may contain additional nutrients such as zinc, iron, and magnesium.

Coverage Area

Regular fertilizers are ideal for smaller plants, especially in gardens. They target the soil surface and are easy to apply.

Meanwhile, a deep tree fertilizer will be better for larger shrubs and trees. These fertilizers act on extensive root systems with a large number of tree feeder roots.

When Trees Need Deep Root Fertilization

Tree roots require deep feeding when the plant is showing signs of stress or nutrient deficiency. Here are some symptoms.

Stunted or Slow Root Growth

There are many reasons for slow root growth. Some include:

• Overwatering or Underwatering: If you do not water the plants properly, the roots may fail to develop properly.
• Poor Soil Quality: A poor soil structure, such as being too clayey or too compacted, can result in poor root growth.
• Nutrient Deficiency: A lack of nutrients, like nitrogen and potassium, leads to stunted root growth. The primary nutrients for root development include phosphorus, sulfur, iron, and zinc.
• Transplant Shock: If you do not transplant a plant properly, its root may be disturbed. Roots take a long time to recover from this trauma.

Deep root feeding can help tackle most of these problems. For instance, it can improve soil structure and compensate for the plant's nutrient deficiency. It also helps the roots recover quickly after transplant shock by providing the necessary nutrients for regrowth.

Reduced Foliage Density

If a tree is showing reduced foliage density, its roots may not be getting enough nutrients. Applying a deep root tree fertilizer may help the tree receive the necessary nutrients, resulting in better foliage density.

Pest Infestations

Trees need deep root fertilization if they are prone to pest infestations. When you fertilize trees at the roots, they are more well-nourished. Such a tree can defend itself against pests more effectively.

Some deep root fertilizers also contain soil amendments, such as compost. These amendments keep pests and bay. They may also help the plant fight pests.

Fertilizing tree roots also improves soil structure. It loosens and aerates compacted soil, making it difficult for pests to penetrate due to increased root growth.

Yellow and Brown Leaves

If the tree leaves are turning yellow or brown, it's possible that the roots are unable to transport nutrients to the top foliage. It's a sign to fertilize the tree roots for proper tree growth.

Benefits of Deep Root Fertilization

Deep root feeding is one of the most effective fertilizer application methods. It has the following benefits:

• Better Nutrient Absorption: When the tree fertilizer is applied to the roots, it is absorbed readily. The method ensures that plants receive nutrients quickly.
• Water Conservation: Deep root fertilization conserves water as it helps prevent run-off of essential nutrients. The method also reduces leaching and maintains soil moisture, which allows the plants to retain more water.
• Increased Disease Resistance: With more natural nutrients, the plant is better equipped to fight diseases and pests.
• Reduced Compaction: A compacted ground limits water and nutrient absorption. Deep root fertilization loosens the compacted ground, allowing for better nutrient uptake.

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