Kelp Products  – Hormones, Amino Acids, Betaines, and Other Beneficial Plant Growth Elements   


It is well documented that commercial seaweed preparations improve plant growth. Many of these effects have been attributed to the presence of growth substances, particularly the cytokinins, which are known to occur at relatively high levels in various seaweeds and commercial seaweed preparations. 1 Although, various kelp types will contain varying levels of auxin to cytokinin ratios. In some cases a certain kelp type will have high levels of cytokinins to much lower levels of auxins while in other instances the opposite will apply.


For instance, the addition of low concentrations of commercial kelp extract (Ecklonia maxima: Kelpak®) in addition to fertiliser has proven to be beneficial in agriculture. It triggers rooting in field crops, increases yields and has other useful effects, such as parasite reduction. Its efficacy has been attributed to the fact that Kelpak® is produced by a cold process, and has a high auxin/low cytokinin ratio.2




Seaweed and seaweed-derived products have been widely used as amendments in crop production systems due to the presence of a number of plant growth stimulating compounds.3


Various kelp types are shown to contain carbohydrates, minerals, and trace elements, amino acids, complex polysaccharides, betaines, and growth hormones such as cytokinins and auxins at different levels. 4


In addition, kelp acts as a mild organic chelator of key mineral elements.


It has been estimated that there are about 9,000 species of macroalgae (kelp) broadly classified into three main groups. Brown seaweeds are the second most abundant group comprising about 2,000 species which reach their maximum biomass levels on the rocky shores of the temperate zones. They are the type most commonly used in agriculture. Among them Ascophyllum nodosum is the most widely researched. Ascophyllum nodosum (rockweed) is a brown seaweed known to grow abundantly in temperate countries such as Canada, France, Iceland, Ireland, Norway, and the United Kingdom.


Below is an analysis of an Ascophyllum nodosum kelp product that is produced in Canada.


Table 1 Composition of Acadian marine plant extract powder 1–1–17

from Ascophyllum nodosum kelp

Physical data

Appearance                                                             Brownish-black crystals

Odor                                                                       Marine color

Solubility in water                                                     100%

pH                                                                         10.0–10.5

Typical analysis


Maximum moisture                                                 6.5%

Organic matter                                                      45–55%

Ash (Minerals)                                                      45–55%

Total nitrogen (N)                                                 0.8–1.5%

Available phosphoric acid (P2O5)                           1–2%

Soluble potash (K2O)                                           17–22%

Sulfur (S)                                                            1–2%

Magnesium (Mg)                                                  0.2–0.5%

Calcium (Ca)                                                       0.3–0.6%

Sodium (Na)                                                       3–5%

Boron (B)                                                           75–150 ppm

Iron (Fe)                                                            75–250 ppm

Manganese (Mn)                                                 5–20 ppm

Copper (Cu)                                                        1–5 ppm

Zinc (Zn)                                                            25–50 ppm

Carbohydrates                                                   Alginic acid, mannitol, laminarin

Amino acids (total 4.4%)

Alanine                                                              0.32%

Arginine                                                             0.04%

Aspartic acid                                                      0.62%

Cystine                                                              0.01%

Glutamic acid                                                     0.93%

Glycine                                                              0.29%

Histidine                                                            0.08%

Isoleucine                                                          0.26%

Leucine                                                              0.41%

Lysine                                                                0.16%

Methionine                                                        0.11%

Phenylalanine                                                    0.25%

Proline                                                              0.28%

Serine                                                               0.08%

Threonine                                                          0.04%

Tyrosine                                                             0.17%

Valine                                                                0.28%

Tryptophan                                                        0.07%



Ascophyllum nodosum extracts contain various betaines and betaine-like compounds (Blunden and others 1986). In plants, betaines serve as a compatible solute that alleviates osmotic stress induced by salinity and drought stress; however, other roles have also been suggested (Blunden and Gordon 1986), such as enhancing leaf chlorophyll content of plants following their treatment with seaweed extracts (Blunden and others 1997). This increase in chlorophyll content may be due to a decrease in chlorophyll degradation (Whapham and others 1993). Yield enhancement effects due to improved chlorophyll content in leaves of various crop plants have been attributed to the betaines present in the seaweed (Genard and others 1991; Whapham and others 1993; Blunden and others 1997).


Numerous studies have revealed a wide range of beneficial effects of seaweed extract applications on plants, such as early seed germination and establishment, improved crop performance and yield, elevated resistance to biotic and abiotic stress, and enhanced postharvest shelf-life of perishable products (Beckett and van Staden 1989, Hankins and Hockey 1990; Blunden 1991; Norrie and Keathley 2006).


Seaweed extract increased fruit yield when sprayed on tomato plants during the vegetative stage, producing large sized fruits (30% increase in fresh fruit weight over the controls) with superior quality. 5


In research conducted by C. M. Steveni et al (1992) on hydroponically grown barley it was shown that two treatments of Ascophyllum nodosum (Maxi Crop) incorporated either into the hydroponic solution or sprayed onto the plants at rates of 1ml per 3 litres resulted in faster growing plants with significant yield increases against controls not treated with Ascophyllum nodosum.


The research noting:




“ Spring barley (Hordeum vulgare cv. Triumph) was grown hydroponically over a 6-week period. Two treatments were incorporated either into the hydroponic solution or sprayed onto the plants at rates of 1 ml per 3 litres. The treatments applied were: (i) a seaweed concentrate prepared from Ascophyllum nodosum (L.) Le Jolis (marketed as Maxicrop Triple), (ii) a ‘Trace element’ treatment incorporating the micro and macro nutrients added to the seaweed extract base to produce the formulated product Maxicrop Triple and (iii) a control treatment. Irrespective of the mode of application, plants treated with Maxicrop Triple grew faster than plants under either of the two other treatments. Elevated growth rates were also found for the ‘Trace element’ treated plants when incorporated into the hydroponic solution.


At the final harvest, plants with Maxicrop Triple incorporated into the hydroponic solution showed increases from 56-63% over the control treatment for the growth characteristics measured. ‘Trace element’-treated plants produced increases of between 25-45 %. When the treatments were sprayed the effect was less pronounced. Maxicrop Triple increased growth characters by 35-38% and the ‘trace element’ treatment gave increases in the range of 2-13%.” 6


[End Quote]


Seaweed components such as macro- and microelement nutrients, amino acids, vitamins, cytokinins, auxins, and abscisic acid (ABA)-like growth substances affect cellular metabolism in treated plants leading to enhanced growth and crop yield (Crouch and others 1992; Crouch and van Staden 1993a; Reitz and Trumble 1996; Durand and others 2003; Stirk and others 2003). Seaweed extracts are bioactive at low concentrations (diluted as 1:1000 or more) (Crouch and van Staden1993a). Although many of the various chemical components of seaweed extracts and their modes of action remain unknown, it is plausible that these components exhibit synergistic activity (Fornes and others 2002; Vernieri and others 2005).


Seaweed extracts have been shown to enhance plant defense against pest and diseases (Allen and others 2001). Besides influencing the physiology and metabolism of plants, seaweed products promote plant health by affecting the rhizosphere microflora. For this reason, kelp is shown to aid beneficial microbe colonization in hydroponic systems and soils.


Seaweeds and seaweed products are shown to enhance plant chlorophyll content (Blunden and others 1997). Application of a low concentration of Ascophyllum nodosum extract to soil or on foliage of tomatoes produced leaves with higher chlorophyll content than those of untreated controls. 7


In research conducted by Stirk et al (2003) thirty-one seaweeds were tested for cytokinins. Findings showed:




“The cytokinin profiles were similar in all the macroalgae regardless of their taxonomy and growing locality. The main type of isoprenoid cytokinins present were zeatins with cis forms being more common than trans forms and isopentenyladenine (iP) derivatives. Only a few dihydrozeatin-type cytokinins were detected at very low levels in only nine species. Aromatic cytokinins were also present but at lower levels and were represented by benzyladenine (BA) and ortho- and meta-topolin derivatives. The topolins were present in greater diversity and concentrations than BA. For all the cytokinin types, the free bases, O-glucosides and nucleotides were the most common with no N-glucosides being detected and ribosides present at very low levels…”8


[End Quote]


In later work, Stirk et al (2004) tested two seaweed concentrates of Ecklonia maxima and Macrocystis pyrifera. Both fresh and stored samples of the two seaweed concentrates were analysed for their endogenous cytokinin and auxin content.


Eighteen and nineteen different cytokinins were detected, respectively, in the two concentrates, with trans-zeatin-O-glucoside being the main cytokinin present.


Auxin-like activity was also detected in both concentrates with the E. maxima derived concentrate having higher biological activity, equivalent to 10−5–10−4 M indole-butyric acid. Indole-3-acetic acid was the main auxin in both seaweed concentrates.9


In research conducted by J. van Staden et al, it was shown that the seaweed concentrate Kelpak, made from Ecklonia maxima applied as a foliar spray or a root drench at transplanting, improved both the vegetative and reproductive growth of marigolds. Of particular significance is that the overall production of seeds (fruits) was increased by as much as 50 percent in some instances.10


Kelpak is a natural liquid extract of the fastest growing seaweed, Ecklonia maxima. It contains a level of 11mg/L of auxins and 31µg/ L of cytokinins (high auxins to cytokinin ratio). It is the only extract produced in the “Cold Cell Burst Method”. This method ruptures the cell walls releasing sap and vital plant hormones without any denaturing. In comparison to other seaweed products, Kelpak contains the highest levels of growth hormones auxins (indole-3-acetic acid, indole-3-carboxylic acid, indole-3-aldehyde, N,N-dimethyltryptamine and N-hydroxyethylphtalimide) and cytokins (transzeatin, ciszeatin, transribosylzeathin, dihydrozeatin, isopentenyladenosine and isopentenyladenine) at 11.0 mg/L of auxin and 0.031 mg/L of cytokinin. The high levels are preserved by the cold cell burst production process which is unique to Kelpak.


Which brings us to our next point…


KELPS – Quality, Types, Plant Species, Genetics, and Optimal Usage Rates and Times


Not all kelp products are of equal quality. For instance, it is generally asserted that powder/granular kelps are of inferior quality to liquid kelps (particularly cold pressed liquid products) due to the production process where dry products are dehydrated using caustic bases under high temperature and high pressure which disintegrates the kelp, removing some of the goodness. However, some extremely good dry products are also available such as Acadian™ (Ascophyllum nodosum) which is sourced and produced in Nova Scotia, Canada. For instance, in trials conducted in California on tomato cultivars, Acadian extracts indicated a range of beneficial responses from 10 to 50 percent increases in average fruit weight, a greater than 20 percent increase in total fruit number, a 50 percent increase in marketable yield, and a 30 percent increase in marketable fruit number. Slight increases in fruit diameter, average fruit weight, and brix were also found.12


Another factor that that will influence quality are kelp species and where the kelp comes from. For instance, kelps are known bioaccumulators of heavy metals and kelps deriving from polluted oceans can have high heavy metal content. These heavy metals can prove detrimental to plant health and be uptaken by the plant, thus entering the food chain.


Additionally, different kelp types possess different biostimulant qualities.


For instance, Ascophyllum nodosum (eg. Acadian), which has a high cytokinin to low auxin ratio, can prove superb for enhancing flower growth (size, firmness, and weight), while a high auxin to low cytokinin ratio kelp (eg. Kelpak which is produced using Ecklonia maxima) may prove detrimental when used in early flower due to high levels of auxins contributing to apical dominance/stretch and cell elongation (traits that are not desirable during the first 2-3 weeks of the flower cycle – or the “stretch phase” as it has become known).


Crop type plays an important role where kelps are concerned. For instance, an Ascophyllum nodosum based product (GOËMAR BM 86) was shown to reduce fruit firmness in two cultivars of strawberry11, while the same product was shown to increase firmness in apples in an earlier study.13


Similarly, studies have also shown that individual cultivars of the same species may respond differently to treatments of seaweed extracts. For example, the same kelp type may improve the yield of one cultivar of potato but not another grown under the same conditions. 14


Additionally, some kelp products are very effective biostimulants when used at the right times, and at the right levels, but may prove detrimental, or provide less benefits when used at too high or too low levels.


Therefore, kelp type, plant type, genetics, product quality, time of use, and usage rates all play an important role in outcomes.


Again, to repeat a point, let me stress something re the use of organics in hydroponic growing systems. It is important to note that where hydroponics is concerned, particularly water based systems (e.g. NFT, deep tank, and aeroponics) it’s important not to overdo it with organic matter or additives. In adding too much organics into the hydro system the proliferation of unwanted microbial life may potentially rob oxygen from the root zone creating a situation where roots are suffocated and pathogenic microbe numbers explode under oxygen starved conditions. This situation is far less pronounced in growing systems that utilize organic media (e.g. soil or coco substrate).


Leading to my next point…. Foliar feeding. (following page)


1) I. J. CROUCH’, M. T. SMITH, J. VAN STADEN, M.J. LEWIS  and G. V. HOAD (1991) Identification of Auxins in a Commercial Seaweed Concentrate

2) D. V. Robertson-Andersson, D. Leitao, J. J. Bolton, R. J. Anderson, A. Njobeni and K. Ruck (2006) Can Kelp Extract (KELPAK) be Useful in Seaweed Mariculture

3) Wajahatullah Khan, Usha P. Rayirath, Sowmyalakshmi Subramanian

Mundaya N. Jithesh,  Prasanth Rayorath, D. Mark Hodges, Alan T. Critchley, James S. Craigie , Jeff Norrie, Balakrishan Prithiviraj (2008) Seaweed Extracts as Biostimulants

of Plant Growth and Development

4) Wajahatullah Khan, Usha P. Rayirath, Sowmyalakshmi Subramanian

Mundaya N. Jithesh,  Prasanth Rayorath, D. Mark Hodges, Alan T. Critchley, James S. Craigie , Jeff Norrie, Balakrishan Prithiviraj (2008) Seaweed Extracts as Biostimulants

of Plant Growth and Development

5) Crouch IJ, van Staden J (1991) Evidence for rooting factors in a seaweed concentrate prepared from Ecklonia maxima.

6) C.M, Steveni, J. Norrington-Davies  and S. D. Hankins (1992) Effect of seaweed concentrate on hydroponically grown spring barley

7) Wajahatullah Khan, Usha P. Rayirath, Sowmyalakshmi Subramanian

Mundaya N. Jithesh,  Prasanth Rayorath, D. Mark Hodges, Alan T. Critchley, James S. Craigie , Jeff Norrie, Balakrishan Prithiviraj (2008) Seaweed Extracts as Biostimulants

of Plant Growth and Development

8) W.A. Stirk, O. Novák, M. Strnad and J. van Staden (2003) Cytokinins in macroalgae

9) W. A. Stirk, G. D. Arthur, A. F. Lourens, O. Novák, M. Strnad and J. van Staden (2004) Changes in cytokinin and auxin concentrations in seaweed concentrates when stored at an elevated temperature

10) J. van Staden, S. J. Upfold & F. E. Drewes (1994) Effect of seaweed concentrate on growth and development of the marigold Tagetes patula


12) J. Norrie PhD (2000) Using Ascophyllum Marine Plant Extracts in Commercial Tomato Production

13) Szwonek E. 2003. GOËMAR BM 86 – wyciąg nawozowy z alg morskich.

14) McHugh, D.J., Lawrence, T. (ed.), 2003. A guide to the seaweed industry. FAO Fisheries Technical Paper 441.