FREE SHIPPING to nominated countries - refer "shipping" tab in each product

Can I mix seaweed fertilizer with normal fertilizer

March 24, 2017

Most gardeners, bonsai artists and orchid lovers, regularly use seaweed extract or seaweed fertilizer and frequently ask “can I mix seaweed fertilizer with normal fertilizer”….

99.9999% of the time , the answer is "YES".

Most seaweed extracts are not technically "fertilizers" and have negligible (if any) NPK content. Therefore, mixing seaweed extract and fertilizer does not normally cause an "overdose" of fertilizer.

Firstly, check if your seaweed extract has an NPK rating. If your seaweed extract has an appreciable NPK (fertilizer content) then do not combine it with fertilizer. You must not “overdose” your plants with fertilizer.

If your Seaweed extract does not have an appreciable NPK (fertilizer content) you may consider combining seaweed extract & fertilizer simultaneously.

If you intend to use a watering can (the old approach), combine the recommended seaweed extract dose into the same watering can as your intended fertilizer. Watering cans are a messy and laborious way to fertilize, but at least it will save you half the time.

Of course, the quicker, easier, less messy and more enjoyable way to apply fertilizer and seaweed extract is to use a fertigate automatic fertilizer unit. You can either apply:

  1. Seaweed extract by itself, or
  2. Mix seaweed extract with fertilizer.

Applying seaweed extract by iteself is easy and straightforward.

Mixing seaweed extract and fertilizer requires a little mathematics to work out the proportions of Seaweed extract and Fertilizer to be combined but will save at least half the application time.

We will consider an example first and then provide a formula you can use. For the following example, assume:

    • Seaweed applied at a rate of 30ml / 9L of water every 20 days
    • Fertilizer applied at a rate of 50ml / 10L of water every 10 days
    • A 4L container will be used to store the mixture.
    • The fertigate automatic fertilizer will be set at the "fertilizer" dose rate ie 50ml/10L (0.5% or 1:200)

In this example:

The prescribed Seaweed dose rate is 30ml/9L. However, we must convert this dose rate to align with the fertilizer water dilution ratio of "per 10L of water".
A rate of 30ml/9L is equivalent to (30ml/9L)*10 = 33.3ml/10L of water.


The specified Seaweed dose frequency is 20 day intervals. Since we will be dosing every 10 days (fertilizer manufacturer's recommendation), we must dilute the seaweed extract by a factor of 10 days / 20 days = ½.

Our equivalent concentration of seaweed extract becomes:
½ x 33.3ml/10L = 16.67ml/10L of water.


In this example the fertigate automatic fertilizer will be set to a dose rate of 50ml/10l. Therefore, to inject Seaweed extract at a higher rate of 50ml/10L we must proportionally dilute the seaweed extract at a ratio of (16.67/50) = 0.3334.


Another way of considering this is we must fill the 4L container with (0.3334) x 4L = 1.3336L of Seaweed extract concentrate.
Since the fertigate automatic fertilizer will be set at the rate specified by the fertilizer manufacturer (50mL/10L) do not dilute the fertilizer concentrate and simply fill the remainder of the 4L container with fertilizer concentrate.


The 4L storage container in this example will have a mixture of: 1.336L of seaweed extract and 2.664L of fertilizer concentrate.


Now simply adopt the following three steps:

Set the fertilizer rate on the dial Place the suction filter into the fertilizer


Start fertilizing - its as easy as that

Step 1
Set the dial to the desired rate

Step 2
Place the suction filter into container

Step 3
Start fertilizing

Having worked through the above example, record your fertilizer and seaweed extract values as below and insert the corresponding values into the formula to calculate the fertilizer and seaweed proportion to be stored in a combined container. (Note – it is important to use the nominated units in the formula)

SWDose = Seaweed Manufacturers recommended dose rate: “aa” mL of seaweed concentrate used per / ”bb” L of water
SWDilution = Seaweed Manufacturers water dilution factor = “bb” L of water
SWFrequency = Seaweed Manufacturers application frequency – every “cc” days
FDose = Fertilizer Manufacturers recommended dose rate: “dd” mL of fertilizer used per / ”ee” L of water.
FDilution = Fertilizer Manufacturers water dilution factor = “ee” L of water
FFrequency = Fertilizer Manufacturers application frequency – every “ff” days
FertigateSetting = fertigate unit dose rate setting “xx” ml/10L (For simplicity use the “FDose” setting)
SCV = Storage Container Volume “yy” Litres which will store the seaweed / fertilizer mixture.


Calculate the volume of Seaweed extract and fertilizer to be placed into the storage container as follows:

Calculate seaweed and fertilizer to combine in a 4L container


Clearly label the container as “Seaweed & Fertilizer Mix” and the “Dose Rate” setting for your fertigate automatic fertilizer.

Combining fertilizer and seaweed extract provides a huge advantage to your plants - ensuring both are available for uptake as the plant requires. It is a refinement on traditional fertigation outlined in this article.


You can also micro-dose the fertilizer and seaweed extract at more frequent intervals. Simply adopt the principles and methodology outlined in this article.

We have been fertigating with a combination of fertilizer and seaweed extract each and every day for a long time. Our bonsai, orchids, vegetables and plants have never looked better. They are healthier, more resistant to pest and disease than ever before.

Consider one of the fertigate range and enjoy watching your garden, trees, bonsai and orchids develop as quickly and as healthy as ours.

Leave a comment

Comments will be approved before showing up.

Also in Fertigation

How to mix Powder fertilizers which have reached soluble saturation levels

March 08, 2018

This article discusses the methods that can be used to assist in dissolving a powder fertilizer that has reached saturation concentrations and is precipitating.

Read More

MixRite 2.5 Automatic Fertilizer Pump

February 26, 2018

The MixRite 2.5 automatic fertilizer unit is an ideal automatic fertilizer pump system for the majority of domestic garden, orchid lover, bonsai artist and small nursery requirements. They can be used with a broad range of fertilisers and seaweed extracts.

Obtaining their source of energy from the mainstream water flow, they are economical to operate and easy and simply to install.

Read More

Units of Fertilizer Concentration

February 11, 2018

This article discusses the globally accepted units of fertilizer concentration or fertilizer dose rates, what they mean, how to convert the fertilizer concentration units and how you can use them.

Read More