All the methods described use liquid fertilizer, which is added to the watering can. These liquid fertilizers are generally water-soluble and can therefore be mixed with water. Some systems also allow the use of fertilizer granules, which are dissolved in the water before watering. Compared to fertilizing with conventional fertilizer, fertilizing with liquid fertilizer offers the following advantages:

• Less time required
• Relatively user-friendly and easy to apply
• Effective and consistent results
• In dry weather, the fertilizer is absorbed into the soil immediately
• It works very quickly (however, the effect is shorter-lasting than with solid fertilizer, so more frequent fertilization is necessary)

To prevent the risk of the fertilizer-mixed water flowing back towards the water source, a check valve should be installed between the water source and the fertilization system. If using drinking water directly from the drinking water system, the stricter regulations regarding drinking water protection must be observed.

Three Types of Systems

Regarding the basic operating principle for fertilizer application, three types of systems can be distinguished:

• Vacuum-based systems
• Pump-based systems
• Very simple systems where the fertilizer is simply flushed from the fertilizer container by means of a water supply

The systems in the first group deliberately create a vacuum to “suck” the fertilizer from the fertilizer container into the irrigation circuit, while those in the second group accomplish this with their own pump. The vacuum-based systems are usually less expensive to purchase and generally also relatively easy to use. The systems in the last group are even simpler, where water is simply added to the fertilizer container and flushed out again as a water-fertilizer mixture. These are specifically aimed at private end users with a focus on ease of use and are not suitable for professional applications.

I will present the different options available on the market below, starting with the simplest and progressing to more complex systems. First, three solutions for manual application, apart from automatic garden irrigation.

Liquid fertilizer container with spray attachment

Liquid fertilizer bottles and canisters (Amazon Link) are available on the market, to which a standard 1/2-inch hose can be directly connected. The fertilizer is automatically added to the watering can in a preset ratio and applied using the spray device integrated into the container. If a water connection and hose are already available, this option can be implemented with zero investment costs.

Special Garden Hose Nozzles with Fertilizer Dispenser

Fertilizing with a special garden hose nozzle equipped with a fertilizer reservoir, which can be refilled, works similarly to the previous method, but even more sophisticated and refined. You connect the hose nozzle to the garden hose and the desired dosage can be adjusted on the nozzle itself; watering is otherwise done as normal. Alternatively, such a garden hose nozzle (Amazon Link) can also be used with cleaning agents for car washing. They cost approximately $15 to $30.

Pump sprayers

These offer a possible alternative to using liquid fertilizer when a hose connection is unavailable. Pump sprayers (Amazon Link) are typically available in 1-gallon or 2-gallon capacities.. How they work: Water and fertilizer are added to the spray bottle, the bottle is sealed, and the pressure inside is increased by pumping several times. This is achieved using a piston with a handle inside the bottle. This piston functions like a piston pump. Because it is relatively large, a small amount of air is pumped into the bottle with just a few pumps, quickly building up the required pressure.

A spray lance is connected to the spray bottle via a hose. Pressing a button releases the pressurized liquid.

These pump sprayers can also be used to apply weed killer or cleaning foam, in addition to fertilizer.

Integrating Fertilization into an Automatic Irrigation System

The fertilization systems presented below are designed for permanent integration into an irrigation system, allowing fertilization to be carried out automatically during watering without any further manual intervention.

Fertilizer Dispenser

These are self-contained systems for private use that can be used immediately in the irrigation system without additional components. Due to their limited capacity and maximum pressure, they are primarily suitable for micro-irrigation. They consist of a fertilizer dispenser with a water inlet and outlet. Examples of this group include the Gardena fertilizer injector and the Chapin fertilizer injectors (Amazon Link).

Gardena Fertilizer dispenser

To use, simply connect the fertilizer dispenser to the irrigation pipeline. If the system is designed for micro-irrigation with a low maximum pressure, a pressure reducer must be installed upstream. Pour the fertilizer into the reservoir and activate the fertilizer mixing mechanism using the lever. Water flows into the reservoir at the bottom, mixes with the fertilizer, and is then flushed out as a water-fertilizer mixture through the outlet at the top of the reservoir and distributed via the irrigation system.

A dosage ratio cannot be set. Instead, the amount of fertilizer to be added is calculated based on the water requirements of the planned irrigation cycle and the liquid fertilizer manufacturer’s dosage recommendation, and then poured into the reservoir. For example: If an irrigation cycle with a water consumption of 10 gallons is planned, and the liquid fertilizer manufacturer’s dosage recommendation is 0.004 gallons or 0.5 fl oz per gallon of water, then 0.04 gallons or 5 fl oz  of fertilizer should be added to the fertilizer reservoir. If water consumption is unknown, it can either be measured or, in the case of a micro-irrigation system, estimated based on the number of drippers used (e.g., if the system uses 40 0.5 gallon drippers, then the water consumption is 20 gallons per hour).

Some systems include a filter that, in addition to liquid fertilizer, also allows the use of filter granules that dissolve in the water flowing through them. The filter prevents undissolved granules from entering the irrigation system.

The fertilizer dosage in such systems is not constant; it is highest at the beginning of the irrigation cycle and then gradually decreases. As the irrigation cycle progresses, the fertilizer-water mixture will contain very little fertilizer.

A crucial factor when choosing a system is the capacity of the reservoir. The reservoir of the Gardena fertilizer dispenser, for example, holds a maximum of only 10 fl oz. This means that refilling is absolutely necessary before each watering cycle. However, the small size might also be insufficient for a single watering session, requiring multiple refills within that cycle. Chapin also offers models with larger reservoirs, which are also suitable for slightly higher pressure (up to 40 psi compared to 22 psi for Gardena).

Gardena Fertilizer Dispenser in a Quick Test

For this article, I put the Gardena fertilizer dispenser through a short test. First, let’s look at what’s included: For around $20, you get the device itself along with two adapters that allow you to convert the inlet and outlet from the larger 1/2 inch supply pipe to the smaller 1/4 inch distribution pipe, so you can also connect the smaller distribution pipe as an alternative. A brief instruction manual is also included, but the operation is essentially self-explanatory.

The fertilizer dipsenser appears to be of high-quality construction, with a heavy, well-fitting plastic lid. It has a maximum capacity of 0.08 gallons. A practical feature: When filling, you can see how much fertilizer has already been added thanks to the markings on the side, making it easy to approach a specific target amount.

A look inside with the practical fill level markings

I simply placed the fertilizer dispenser in front of a micro-irrigation zone. Specifically, after the pressure regulator, as the pressure inside the device must not exceed 22 psi.

This is how to connect the device (pressure regulator on the left).

The installation direction is indicated by an arrow on the device. Before starting, the lever must be set to “Mix” and then irrigation can begin. The other setting, “Service,” is for draining the water from the bottom of the reservoir to empty it. In my test, the operation worked flawlessly, but the micro-irrigation area I watered would probably be too large for real-world use, as evidenced by the fact that the fertilizer solution was washed out of the device in no time. In practice, I would doubt that the fertilizer would then be distributed evenly to the plants.

Conclusion: The Gardena fertilizer injector works reasonably well, but in my opinion, it is really only suitable for very small micro-irrigation applications, such as on a balcony or a small patio. As soon as the area becomes larger, I would recommend a system with a larger reservoir.

Alternatives to the Gardena Fertilizer Mixer

Besides Gardena, I am only aware of the Chapin Hydrofeed devices with the same principle. There is the Hydrofeed 4700 to 4702 (Amazon Link), a device that is built on the same principle as the Gardena fertilizer mixer, but is designed for hanging rather than standing installation. It is offered with fertilizer capacities of 16, 24, or 32 ounces. And then, from the same company, there is the much larger Hydrofeed 4720 with a comparatively large 2 gallon tank and an injector section separate from the tank.

Venturi Injector

This method of fertilization, known for centuries, utilizes a physical principle: When a liquid is forced through a constriction, its velocity increases at that point, while the outward pressure exerted by the liquid decreases. This can be explained by the formula: Total pressure = Flow pressure + Static pressure. Therefore, if the flow velocity (= flow pressure) increases, the outward pressure (= static pressure) must decrease. If the constriction through which the water is forced through a pipe is narrow enough, there is no pressure at all on the outer walls; instead, a vacuum is created. This means that if there were a hole in the outer wall at this constriction, no water would escape; instead, if you placed your finger on it, you would feel a suction.

The so-called Venturi nozzle utilizes this principle. A smooth-walled pipe is significantly narrowed in the middle, and a suction hose leads from this constriction, utilizing the vacuum to draw in a liquid or gas.

Example of a Venturi injector in use

Alternatively, the Venturi nozzle can also be installed in a bypass branch that diverts from the main line. Such a bypass has the advantage that only a portion of the water flow passes through the Venturi nozzle (allowing for larger volumes of water) and that a valve installed in the main line can be used to slow down the water flow, creating a controlled pressure differential and thus controlling the intensity of the fertilizer application.

In agriculture, such Venturi nozzles have been used for fertilization for many decades. Their advantage: They utilize existing water pressure to deliver the liquid fertilizer, and they are very easy to install and compatible with fertilizer tanks of virtually any size. Disadvantages: The Venturi principle requires pressure, and the fertilizer intake results in a loss of water pressure. Furthermore, the fertilizer dosage is pressure-dependent and therefore not constant under fluctuating pressure.

More information on how the Venturi injector works, including a short test report, can be found in a separate article: Fertilizing with a Venturi Injector

Differential Pressure Fertilizer Tanks

These systems function similarly to the previously described fertilizer injectors, but are significantly larger and additionally utilize a bypass (diversion) to create a controlled pressure differential. This allows for precise control over the force with which the water-fertilizer mixture is drawn from the tank. Part of the water flow continues directly through the main line, while another part takes the detour via the new bypass into the fertilizer tank. There, the water mixes with the fertilizer, and the resulting mixture is then transported and distributed.

A valve is installed in the main line at the bypass point to slow down the water flow. The greater the slowdown, the greater the pressure differential between the tank inlet and outlet, and consequently, the stronger the water-fertilizer mixture is drawn from the tank.

As with fertilizer injectors, the dosage in differential pressure tanks is not constant: The fertilizer concentration in the dispensed water is high at the beginning, decreases continuously with the water flowing into the tank, and is very low at the end of the irrigation. Therefore, as with fertilizer injectors, there is a risk of overdosing fertilizer in some areas and underdosing it in others.

Compared to a Venturi injector, the application is somewhat simpler. However, significantly less controlled fertilization is possible. The generation of differential pressure also results in a pressure drop in the fertilizer tank.

Dosing Pumps

These are mechanical pumps, meaning they operate without an electrical connection. They are also known as “Positive Displacement Injectors.” The principle is similar to that of another type of piston pump, the traditional hand pump. Water from a pump or the mains water supply flows into the pump and drives the piston. The piston’s stroke adds fertilizer to the water, and the water-fertilizer mixture is then pumped on the other side of the pump. The dosing ratio can be adjusted on the pump.

Dosing pumps are a very professional method of fertilization and have the significant advantage that the dosing ratio remains constant regardless of the water pressure and flow rate, as the same amount of water and fertilizer is mixed with each up-and-down movement of the piston. However, they are considerably more expensive than Venturi nozzles. As with Venturi nozzles, dosing pumps also experience a certain water pressure loss, which depends on the water flow rate. For example, the Tefen Mixrite TF-125-04 has a pressure loss of 3 psi at a flow rate of only 50 gallons per hour and 17 psi when operating at the maximum flow rate of 660 gallons per hour.

Dosing pumps from brand-name manufacturers like Dosatron or Tefen start at around $500, but generic models are also available on Amazon and eBay starting at approximately $150 (Amazon Link).

Electric Dosing Pumps

These are the top-of-the-line fertilization systems. They function on the same basic principle as the previously described dosing pumps, by dispensing water and fertilizer in a predetermined ratio and then pumping it onward. The only difference is that the drive is electric, for example, with a pump controlled by the water flow. They are significantly more expensive than their manual counterparts and therefore generally unaffordable for private users.

Conclusion and Recommendation

Differential pressure fertilizer tanks are only used in a few regions of the world and are rarely available on the market. Due to their high price, electric dosing pumps are not a viable alternative for private users. This leaves you with four basic alternatives:

• Manual watering using special fertilizer sprayers, fertilizer containers with spray attachments, or pump sprayers
• Fertilizer mixing dispenser
• Venturi nozzle
• Mechanical dosing pump

If you don’t want to invest much, have minimal setup effort, and don’t mind a little manual work when fertilizing, then the options mentioned at the beginning of this report for integrating liquid fertilizer into a manual system are worth considering.

For small and medium-sized micro-irrigation systems, fertilizer mixing dispenser offer a very simple and effective alternative. The container is simply placed in front of the micro-irrigation area, and the fertilizer is gradually flushed out during watering. For small-scale applications, where only a few plants on a balcony or patio are being micro-irrigated and the water flow is low, the Gardena fertilizer dispenser is suitable. For medium-sized systems, Chapin fertilizer injectors are recommended, and for larger micro-irrigation systems, the large 2 gallon Chapin Hydrofeed 4720 tank is ideal.

A more professional fertilization method, allowing for active regulation of fertilizer dosage and ensuring consistent application, is possible with Venturi injectors. These have been used in agriculture for many decades and can be easily integrated into an existing irrigation system using a bypass. The tank size is flexible, as any suitable container can be used. A more powerful pump is required, as the Venturi nozzle noticeably reduces water pressure.

For home users, the ultimate solution is the mechanical dosing pump. This system is significantly easier to use than the Venturi injector and guarantees consistent dosing even under fluctuating pressure. The fertilizer dosage can be easily adjusted via a lever. However, especially with brand-name equipment, it is many times more expensive than the Venturi injector.

Der Beitrag This way, garden irrigation can be used for fertilization. erschien zuerst auf Irrigation Blog for Do-it-yourselfer.

Principle of the Venturi Nozzle

A Venturi injector is based on the Venturi nozzle invented by Giovanni Battista Venturi over 200 years ago: This is a smooth-walled tube with a sharp constriction in the center, from which an opening leads downwards. At the constricted point in the tube, due to the laws of physics, the velocity of the water flowing through it increases (= increasing flow pressure), while at the same time the static pressure on the tube wall decreases; total pressure = flow pressure + static pressure. The constriction in a Venturi nozzle is designed so large that the static pressure at the constriction not only decreases, but even creates a negative pressure (vacuum). This means that no water escapes from the opening leading away from the constriction; on the contrary, a suction is created.

How a Venturi Injector Works

The suction created by the flow through the Venturi nozzle is used to draw in a gas or liquid via a hose mounted at the constriction. In the application described here, liquid fertilizer is drawn in. For this purpose, the hose is simply led away from the Venturi nozzle into a container containing fertilizer. As soon as irrigation is running, the created suction ensures that the fertilizer is gradually mixed into the irrigation water.

At the opening from which the fertilizer intake hose leads, a mechanism is installed in the Venturi nozzle that prevents water from flowing into the fertilizer container. In practice, this would occur when irrigation is stopped, thus creating pressure at the intake opening instead of a negative pressure. The water remaining in the irrigation system would then be forced outward and flow into the fertilizer container.

In most Venturi injectors, the backflow prevention mechanism works with a small spring that pushes a plastic ball in front of the outlet, thus closing it. Only when sufficient suction is applied does the ball retract, opening the outlet so that the fertilizer can be drawn in.

Intake outlet ready for use and below with removed seal, ball and spring

The ratio of fertilizer addition is primarily determined by the following three parameters:

• Diameter of the Venturi nozzle and the nozzle constriction
• Inlet pressure at the inlet of the Venturi nozzle
• Outlet pressure at the outlet of the Venturi nozzle

The following applies: The greater the pressure difference between the inlet pressure (at the inlet of the nozzle) and the outlet pressure (at the outlet of the nozzle, after passing the constriction), the greater the suction effect and, consequently, the more fertilizer is added. This difference is achieved, on the one hand, by the constriction in the Venturi nozzle, as the water loses pressure due to the strong friction when passing through the constriction. The narrower the constriction, the greater the pressure loss. When installing the Venturi nozzle via a pipe bypass, the pressure difference can be further increased by deliberately slowing the water flow upstream of the outlet side of the Venturi nozzle with a valve, allowing the fertilizer dosage to be controlled according to your preferences.

Depending on the model, Venturi injectors require at least a 20 to 30% pressure difference between the inlet and outlet of the nozzle to function. A difference of around 50% typically achieves the maximum possible fertilizer dosage. The minimum pressure difference required to draw in fertilizer cannot be achieved with all Venturi injectors and at all inlet pressures using only the Venturi nozzle; in some cases, creating an additional pressure difference using a bypass is absolutely necessary.

The maximum technically achievable mixing rate for a Venturi injector is a maximum of 10% (i.e., 1 gallon of fertilizer to 10 gallons of water). For the sake of completeness: In addition to the size and design of the Venturi nozzle, the inlet and outlet pressures, other factors can have a minor impact on the dosage ratio: the liquid fertilizer used (viscous or watery), how deep the fertilizer container is placed below the nozzle, the outside temperature, and the elevation of the application site.

The diameter of the Venturi nozzle, the inlet pressure, and the outlet pressure also determine how many gallons of water per hour can flow through the nozzle in this configuration. Quality manufacturers list these parameters for each nozzle size and different inlet and outlet pressures in performance tables. Below is the example performance table for Irritec’s Venturi injectors:

Performance table of Irritec Venturi injectors

The first column shows the inlet pressure, followed by a range of possible outlet pressures. For each combination of inlet and outlet pressure, the corresponding water flow and fertilizer output are listed. This is for four different Venturi injector models ranging in size from 3/4 inch to 2 inches.

An example explains how to read such a table:

Using a 3/4-inch injector, an inlet pressure of 4.10 bar (60 psi), and an outlet pressure of 3.0 bar (43 psi), a flow of 36 liters per minute (10 gallons per minute) or 2,160 liters per hour (570 gallons per hour) is possible, and the fertilizer addition would be 66 liters (17 gallons) per hour. With a 1-inch injector, the water flow at the same pressure would be 4,560 liters per hour (1.200 gallons), and the fertilizer addition would be 230 liters (60 gallons).

What determines the outlet pressure?

The outlet pressure is determined by the requirements you want to meet with the fertilizer water. If the water were simply allowed to flow freely out of the pipe immediately after leaving the Venturi nozzle, a pressure close to zero on the outlet side would be sufficient. In this case, a valve installed in the bypass could reduce this pressure to near zero, thus exploiting the maximum possible pressure difference and achieving the highest possible fertilizer dosage.

However, if the fertilizer water still has to exert considerable pressure after leaving the Venturi nozzle – as is usually necessary in an irrigation system – to travel the distance through the irrigation pipeline and then ensure the sprinklers extend and function correctly, a significantly higher pressure is required on the outlet side.

This is essentially the same consideration as when calculating the water flow rate in an irrigation system. For example, if the sprinklers require 40 psi and there is a further pressure loss of 10 psi in the pipeline due to friction, then 50 psi of pressure would be needed on the outlet side just to exert the necessary static pressure in the irrigation system. At such a pressure, however, the entire output pressure would be used for static pressure, leaving no dynamic pressure to drive the water through the pipes. For irrigation to function with a reasonable amount of water, a slightly higher output pressure than 50 psi would be required. According to a practical example used here in the blog, for example, with the water source used there, you would need 60 psi to achieve a water output of 280 gallons per hour with a pressure requirement of 50 psi in the irrigation system.

This shows that in practice, you have to weigh and balance between higher fertilizer dosage and still sufficient output pressure, and in many cases, you will have to focus on the lowest possible dosage. Unless you use the Venturi injector for micro-irrigation, which has significantly lower pressure requirements, or you have a very powerful pump available that still has considerable reserves for everyday irrigation needs.

Advantages and Disadvantages of Fertilization with a Venturi Injector

The main advantage of fertilization with a Venturi injector is that it is very easy and cost-effective to implement. Furthermore, Venturi injectors are simple and have no moving parts, so almost nothing can break during operation and they are therefore very low-maintenance.

A significant disadvantage is that the Venturi nozzle relies on the existing water pressure to function. Bernoulli’s law “Total pressure = flow pressure + static pressure” only applies one-to-one to frictionless fluids, which water is not. Therefore, when water flows through the constriction of the Venturi nozzle, friction losses occur and, consequently, pressure losses. The function of the Venturi nozzle is based precisely on this pressure loss, which leads to the pressure difference.

Depending on the nozzle model, a pressure drop of at least 20 to 25% is required for proper functioning. If the natural pressure loss through the nozzle is insufficient, the water must be additionally slowed down in a bypass system with a valve.

Consequently, the use of a Venturi injector leads to a certain pressure loss, so that the pressure ratios previously present in an irrigation system are no longer 1:1, and irrigation may then no longer function as perfectly as before (reduced uniformity). It is comparatively easy to use in micro-irrigation systems, which operate at low pressure. Therefore, reducing the pressure hardly plays a role in such systems.

For use in conventional irrigation, e.g., for watering the lawn, a powerful pump is advantageous, so that sufficient pressure remains for irrigation after the water has passed through the Venturi nozzle, and irrigation continues to function properly.

Compared to fertilizer systems with a dosing pump, a Venturi injector also has the disadvantage that the amount of fertilizer delivered depends on the pressure conditions. This makes it difficult to precisely adjust and maintain the fertilizer dosage, especially if the irrigation system is subject to fluctuating pressure conditions.

Finally, correctly adjusting the Venturi injector for the first time requires some effort, especially if you want to set the dosage to a predetermined level. After setup, the installation is ideally left untouched so that the desired adjustment can be used permanently.

How to Install the Venturi Injector

The Venturi Injector is typically installed in the main pipeline, i.e., in the section of the pipe at the beginning of the system that is passed through during each irrigation run, before the main line then splits into several branches for the individual irrigation sectors.

To prevent the risk of backflow of water mixed with fertilizer toward the water source, a backflow valve should be installed between the water source and the fertilization system, or the Venturi nozzle should be isolated from the main system with manual valves after fertilization. If drinking water is used directly from the drinking water system, the stricter regulations regarding drinking water protection must be observed.

The Venturi Injector can either be installed in-line with the main pipeline or in a branch (bypass) that diverts from the main pipeline to the Venturi Injector and returns to the main pipeline after the fertilizer has been absorbed.

Such a bypass installation has the following advantages:

• With a valve installed in the main line at the level of the bypass between the bypass inlet and bypass outlet, you can control the pressure difference between the inlet pressure and the outlet pressure of the Venturi nozzle, thus adjusting the fertilizer dosage. Some manufacturers even specify this type of installation to ensure their injector functions properly, or even strongly recommend it, because the Venturi nozzle alone cannot create the necessary pressure difference, or not in every pressure configuration.
• Furthermore, a bypass solution has a positive effect on water flow, as some of the water can bypass the Venturi nozzle and take the direct route through the pipeline. This enables higher flow rates than the Venturi nozzle itself would allow.
• The bypass can be deactivated relatively easily with valves installed in between, so that during normal non-fertilizer irrigation runs, the water does not have to flow through the Venturi nozzle. If the injector were installed directly into the main line, it would have to be removed every time after use to achieve the same result. The bypass, on the other hand, only needs to be installed once and can then remain as it is permanently.

Below are four possible installation methods for a Venturi injector from the Irritec user manual. In addition to the connection directly into the pipeline and the standard bypass connection, two alternative connections with an additional pump are also listed:

Four possible installation types

The Venturi injector should always be mounted horizontally or, alternatively, vertically upward (i.e., inlet at the bottom and outlet at the top). A vertically downward position can cause suction problems. The water must flow through the nozzle in the specified direction; this direction is indicated on the nozzle.

By installing a pressure gauge on the inlet and outlet sides of the bypass, the inlet and outlet pressure can always be precisely monitored, or a specific pressure difference can be set using a valve.

Since airtight connections are important for proper operation, it is recommended to use PE tape or other sealing material on the threads during installation. Ideally, the complete injector, i.e., both the nozzle and the suction hose, should be purchased from the same manufacturer to ensure optimal compatibility.

The suction hose is suspended completely down to the bottom of the fertilizer tank so that the fertilizer can be drawn all the way to the bottom. At the end of the suction hose there is usually a small filter basket that prevents the suction of larger protective particles.

How to Choose a Suitable Venturi Injector

The most important selection criterion is the size of the injector! This is not determined by the size of the pipeline used in the irrigation system, but by the available pressure and water flow rate. Specifically, the water flow rate achieved during operation, not the maximum available! This is further exacerbated by the fact that the Venturi nozzle requires a significant pressure reduction of 20% or more to function, and the water flow rate when using a Venturi nozzle will therefore be somewhat lower than in previous irrigation runs without a Venturi nozzle. Unless you haven’t yet fully utilized the potential pump capacity or the power from the domestic water supply, so you still have some reserves.

If in doubt, or if you’re unsure about the water flow rate, it’s better to buy a smaller Venturi injector!

If the injector is too large and the specified flow rate is not reached, the injector will not draw in any fertilizer. If the injector is too small, however, fertilization will work perfectly, but the injector will limit the flow. This problem can be solved relatively easily by incorporating it into a bypass so that excess water can bypass the nozzle.

Note: Micro-irrigation sectors are particularly problematic for Venturi injectors if they have very low water flow rates. Here, you must carefully find a suitable injector or, if that is not possible, use a different fertilization system altogether.

Regarding water flow, it is important to note that even with the same diameter, Venturi injectors can have very different performance characteristics. There are 3/4-inch injectors designed for high water flow and others for low water flow. The manufacturer Mazzei, for example, offers both the IM34L model with a minimum flow rate of 240 gallons/hour at 50 psi inlet pressure and the IM34H model with a minimum flow rate of 420 gallons/hour at 50 psi inlet pressure in 3/4-inch sizes. They also offer a 1/2-inch injector with a low flow rate of 60 gallons/hour or a high flow rate of 150 gallons/hour (IM12L and IM12H). The 3/4-inch Irritec model I tested requires approximately 500 gallons/hour at an inlet pressure of 50 psi.

The possible fertilizer dosage is only a secondary selection criterion. Liquid fertilizer manufacturers specify a specific dosage ratio for their products, which the injector should be able to achieve. However, it is particularly important not to apply the fertilizer too concentrated, as this could damage the plants. However, this problem will rarely occur with Venturi injectors, as higher dosages require more pressure. When fertilizing with an irrigation system, it is generally recommended to apply the fertilizer slowly, as this allows for greater uniformity.

Products Available on the Market

Complete Venturi injectors, consisting of a nozzle and intake hose, as well as nozzles and intake hoses separately, are available on the market. Venturi injectors are available either as a standalone product, i.e., just the nozzle and a matching intake hose, or as part of a pre-assembled bypass. This saves you the trouble of assembling such a bypass yourself.

Numerous no-name products are available, as well as products from brand manufacturers such as Netafim, Irritec, or Mazzei. No-name Venturi injectors start at $20 to $30, while brand-name products cost approximately $60 to $100. A Venturi injector in a pre-assembled bypass solution will cost approximately $30 to $200 more, depending on the quality of the bypass and whether it includes a built-in pressure gauge. Some injectors also offer a way to adjust the dosage by using a valve on the intake hose to slow the suction.

Venturi injectors on Amazon:

Unlorspy 2Pcs Black Venturi Injector Tube 1/2 Inch Agriculture Garden Fertilizer Injector Plastic Irrigation Venturi Injector for Irrigation Systems (1/2 Inch)

$9.69 (as of 19. March 2026 23:12 GMT +01:00 - More infoProduct prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on [relevant Amazon Site(s), as applicable] at the time of purchase will apply to the purchase of this product.)

AYLIFU 3/4Inch Black Irrigation Venturi Fertilizer Injector Tube Venturi Fertilizer Mixer Injector for Outdoor Garden Agricultural Irrigation Equipment Tools

$8.99 (as of 19. March 2026 23:12 GMT +01:00 - More infoProduct prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on [relevant Amazon Site(s), as applicable] at the time of purchase will apply to the purchase of this product.)

Ozone Venturi Injector for Cold Plunge, Ice Bath, Spa & Pool Pumps, 3/4" Barbed Inlet/Outlet, 1/4" Ozone Port, PVC Water Treatment & Fertilizer Injection for Irrigation

$27.99 (as of 19. March 2026 23:12 GMT +01:00 - More infoProduct prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on [relevant Amazon Site(s), as applicable] at the time of purchase will apply to the purchase of this product.)

UPLYKKE Irrigation Venturi Fertilizer Injector Kit - 1 inch NPT Threaded Interface Venturi Mixer Injector for Automatic Drip Irrigation System Agriculture Garden Water

$19.99 (as of 19. March 2026 23:12 GMT +01:00 - More infoProduct prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on [relevant Amazon Site(s), as applicable] at the time of purchase will apply to the purchase of this product.)

ApplianPar 3/4 Inch Garden Irrigation Device Venturi Fertilizer Kit Mixer Injector Switch Dispenser Water Tube Set

$15.05 $13.20 (as of 19. March 2026 23:12 GMT +01:00 - More infoProduct prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on [relevant Amazon Site(s), as applicable] at the time of purchase will apply to the purchase of this product.)

LQ Industrial 3/4Inch Black Irrigation Venturi Fertilizer Injector Agriculture Irrigation Device Tool

$8.99 (as of 19. March 2026 23:12 GMT +01:00 - More infoProduct prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on [relevant Amazon Site(s), as applicable] at the time of purchase will apply to the purchase of this product.)

Practical Test of the Irritec 3/4-Inch Injector

To give you a concrete example of an application and a starting point for your own further considerations, I tested the Irritec 3/4-inch injector in practice. I tested it with a fairly powerful Grundfos Scala 1 5-55 pump, which still has reserves for its current irrigation task. A pressure of approximately 60 psi is required in the area to be irrigated (40 psi sprinkler, 10 psi pipeline, 10 psi elevation difference when drawing water from the well). The hourly water flow in the tested zone for irrigation without fertilization has so far been approximately 700 gallons.

I screwed the nozzle and intake hose together to form the injector as they came, without any additional sealing material, and installed the injector directly into the pipeline, without a bypass. The intake hose simply hung from there into a standard bucket filled with fertilizer. A very simple design, but perfectly adequate for the test purpose. For permanent use, it could and should certainly be made even more stable and visually appealing.

My simple installation, limited to the essential function, for test purposes

And then an irrigation run was started immediately. Result: The fertilizer intake in the Venturi injector worked perfectly and powerfully, but the sprinklers no longer had the necessary pressure to extend properly and only irrigated at half-mast with significantly reduced throw distances.

Interim conclusion: As expected from the manufacturer’s performance tables (see earlier in the article), the Venturi nozzle limited the maximum possible water flow due to the constriction in the nozzle. This would not be practical in this configuration, as the fertilizer would be distributed very unevenly due to the completely inadequate throw distances.

I then tested the same setup in a second zone, which has a significantly lower water flow of 450 gallons per hour. With this zone, irrigation worked perfectly as usual, with the usual spray distances. And the fertilizer intake also continued to work flawlessly.

Test with installed bypass

I conducted my next test again on the large 700-gallon zone. I quickly built a bypass branch using connectors, pipe sections, and a valve. The bypass branches off downward from the main line, then runs through the Venturi nozzle, and returns to the main line. Parallel to this, the main line continues directly, with an additional valve installed after the branch to the Venturi nozzle to regulate the pressure.

Venturi nozzle integrated into a bypass

In my first test run with the bypass solution, I left the valve fully open so that the water could flow through unhindered. As expected, the irrigation system received sufficient water and functioned as normal. However, the Venturi nozzle did not suck in any fertilizer in this way, as the nozzle constriction was not sufficient in this configuration to generate the required pressure difference.

I then gradually closed the valve until the intake hose began to draw in fertilizer. This was easy to control, and at the lowest possible dosage, where the fertilizer was only sucked out of the bucket very slowly, the irrigation felt almost normal, with only a very slightly reduced throw distance. But even at a higher dosage, it continued to function quite well, with throw distances that were still usable in practice.

Interim conclusion: With a bypass branch, you can easily get closer to the desired result and find a suitable balance between fertilizer dosage and pressure loss.

Test conclusion

The Venturi injector met my expectations: Setup is straightforward and inexpensive, and you can quickly achieve a usable result. Since it allows for significantly more flexible and precise adjustment, I would definitely prefer the bypass installation to the in-line installation for long-term use. The additional installation time only takes a few minutes, or if that’s too tedious for you, you can also purchase ready-made bypass solutions.

Note: After fertilization is complete, you should continue to water with clean water for about half an hour to ensure that all fertilizer residues are washed out of the system and that no algae or microorganisms can form.

Der Beitrag How to fertilize with a Venturi injector erschien zuerst auf Irrigation Blog for Do-it-yourselfer.

Der Beitrag How to properly fertilize your lawn! erschien zuerst auf Irrigation Blog for Do-it-yourselfer.