What seaweed can do for your crop

The market offers us a wide variety of products to improve the state of our plants in the garden. Not all are good and not all are bad, you simply have to distinguish, based on your own experience, between them. The same happens with seaweed extracts , where good products achieve very satisfactory results in the development of our crops. Let’s see what seaweed extracts are all about.


Agriculture increasingly has more instruments and tools to achieve the best results. Now there is an extensive catalog of biostimulants (amino acids, seaweed, hormonal products, rooting agents, etc.) that expand the catalog beyond the common macro and micronutrients.

These stimulants began their journey in a highly technical and specialized market such as that of marijuana fertilizers , and little by little they have been introduced to less competitive markets such as cereals, horticulturals, fruit trees, subtropics, etc.

In all this shed of biostimulants (which by the way, will soon have their specific regulation), we find seaweed extracts. Although here we must differentiate between different types of algae, current Spanish legislation only recognizes 2 different types:

  • Ascophyllum nodosum
  • Ecklonia maxima

[alert style = »yellow»] And where do the rest fit? Well, as nutritional sources of elements (potassium, for example), amino acids (like spirulinas), etc. Of course, this must change in the future since many fertilizer houses live off a catalog related to these raw materials. [/ alert]


  • Stimulates and accelerates seed germination.
  • Increases the size of tubers and facilitates their development.
  • Activator and initiator of root growth.
  • Improves and increases production.
  • It allows a greater homogeneity in the size of the fruits.
  • Source of phytoalexins (the natural defenses of plants).
  • Increases the ability to capture nutrients provided in the compost.
  • Reduction of plant or crop aging.
  • Increases resistance to drought, salinity and stress, such as potassium.
  • Antioxidant action, being a precursor of natural hormones for plants.
  • Positive effect on flowering and fruit set.


  • Soil acidity corrector.
  • Corrector of nutritional deficiencies (macronutrients and micronutrients).
  • Stabilizing effect of the soil structure.
  • Activator of the microorganisms present in the soil (food source).
  • Complexing effect of soil minerals.

Basically, the effect that seaweed promotes on plants is based on acting as a trigger or enhancer in the assimilation of nutrients (by enzymatic activation). In the soil it also achieves positive effects, based on improving the physical properties of the soil, such as moisture retention, by cellulose, or as a food source for positive bacteria and microorganisms.


And again we return to the same thing. As with amino acids, nematicide products or many others, an important factor that defines the quality of seaweed is the extraction process. Like a good ribeye of veal, it is not the same that it is fresh than frozen, right?

In this case, the same happens, if the extraction and packaging process is “fresh”, that is, it is the pure extract of the algae, it will retain many more properties than if we take the dry extract of algae or freeze it. In this case, although it also provides properties to plants, the level of phytohormones is much lower (it is lost in the packaging process, such as vitamins).

As you will see below, more than the interest in the nutritional content that this product may have, what is most interesting are the compounds based on polysaccharides such as alginic acid, laminarins, auxins , etc. However, all these compounds, as we have commented, are lost in the manufacturing process, if we modify their physical properties.


The nutritional composition of seaweed is not notable for the large amount of nutrients it provides to plants (the relationship is more phytohormonal). So that you can see an example of the average composition of an extract of algae such as Ascophyllum nodosum ,  Macrocystis pyrifera  or  Gelidium robustum.

  • Total nitrogen (N): 0.05-0.145%
  • Phosphorus (P2O5): 0.001-0.02%
  • Potassium (K2O): 0.08-2%
  • Calcium (CaO): 0.015-0.02%
  • Magnesio (MgO): 0,015-0,02%
  • Iron (Fe): 5-10 mg / L
  • Zinc (Zn): 15-250 mg/L
  • Organic matter: 2.5-3.5%

As you can see, the concentrations are quite low, so it should not be considered as a nutrient but as a stimulant . In the content, which is not declared in percentage, we must add everything that we have commented before, phytohormones (auxins, gibberellins, etc.), polysaccharides (lamarin, alginic acid, mannitol, fuicodan, galactans, celluloses, etc.

All of this is what is really interesting in seaweed extracts . However, it is difficult to differentiate between products for the same reason, said contents are not declared in the technical sheets or on the labels.

Here it is interesting to see if the seaweed extracts have been treated or are pure liquefied and packaged extracts. When they have low doses (in%), they are usually prepared or powdered seaweed extracts that are later re-linked with water.


Seaweed is to plants as chocolate is to us, so to speak. It is a growth enhancer based on enhancing the enzymatic activity of the crop through the production of phytohormones .

Therefore, each farmer uses it differently. There are those who can afford to apply it continuously to their cultivation. Others, in delicate moments of the crop (after environmental stress, in flowering and fruit setting stages, at the beginning of the crop, etc.).

There are also those who combine it with phytosanitary products or nutritional complexes to achieve a faster effect in its assimilation. This can be based on the organic complexation technique, as it is also done with carbon (C).


Although each product based on seaweed will have recommendations, in this case nothing happens to happen to us (the one that will suffer the most will be our pocket). However, we provide a series of common values ​​that can guide us when calculating the amount we have to buy and the effect we want:

  • Fruit trees: 100-300 cc / hl (foliar application). 5 L / ha applied in irrigation.
  • Vegetables in general : 100-200 cc / hl (foliar application). 5 L / ha applied in irrigation.
  • Seedlings:  150 cc / hl (foliar application), when the plant reaches 10 cm in height.
  • Grass:  200-400 cc / hl (foliar application), at the beginning of spring.
  • Olive grove  150-300 cc / hl (foliar application). 5 L / ha under irrigation.
  • Vine:  200-250 cc / hl (foliar application), 5-8 L / ha in irrigation, to start budding, flowering or fruit set.

So, as a conclusion, if at a certain moment you need a stimulus to get out of an environmental or biotic stress (caused by a plague or disease), you can resort to seaweed extracts.

Leave a Reply

Your email address will not be published. Required fields are marked *