Seaweed Extract Application in Turfgrass Management
By Tim Butler
Kelp, (which is better known as seaweed) has been used as a fertiliser on turf for many years. I'm sure that many of you have at one stage or another used some form of seaweed extract in your management programmes. Traditionally kelp was collected off beaches, composted and applied as a fertiliser or top dressing. There are many different kinds of Kelp. Ascophyllum nodosum, also called "Norweigan Sea Kelp" is the most readily available.
Most seaweed fertilisers are derived from Kelp that has been harvested, dried and ground. The one big question that many people ask me is do seaweeds work?. The simply answer that I give is that it depends on what you expect seaweed extracts to do. From my experience, I feel that when seaweed extracts were introduced to turfgrass, their potential benefits were somewhat overstated.
Many turfgrass managers believed that seaweeds were a wonder product that would eliminate many problems that they encountered. I believe that this over expectation left many seaweed users disillusioned with the product and many felt that seaweed extracts were of no use. Firstly I would like to explain what exactly seaweed extracts may do for you as a turfgrass manager.
Seaweeds and Turfgrass Nutrition.
Seaweed contains major and minor plant nutrients, trace elements; alginic acid; vitamins; auxins, gibberellins and cytokinins. A major misconception that many people have is that seaweed extracts will compensate for a reduction in applied nutrients. It is true that seaweeds contain some nutrients, although, from my experience these nutrient amounts are often very low and will not dramatically add to the amount of nutrients available to the plant.
However I feel that by applying a seaweed extract, nutrient availability within the soil may be increased. There is no guarantee, however some researchers have found beneficial effects. Nowadays, many seaweed extracts are combined with foliar fertiliser blends and marketed as biostimulant products.
In fact, there are hundreds of such products available and it often gets confusing trying to choose any specific product. Probably one of the things that you should realize is that seaweed extract can be either cold or heat extracted and some in the industry believe that cold extracted seaweed may be more beneficial.
I believe that one of the main benefits of applying seaweed extracts is in increasing turfgrass stress tolerance levels. This is of particular importance in golf courses and sports pitches, which receive large amounts of wear. The positive impact of seaweed extract application is mainly attributed to the complex mix of betaines within liquid seaweed extract which raises the plants stress thresholds to higher levels. Compounds, such as betaines are thought to play a vital role in cytoplasmic adjustment in response to stress.
Seaweed extracts contain phytohormones and the stimulatory effects of seaweed extract, particularly for turfgrasses growing under stresses have also been attributed to its hormonal activity, especially that of cytokinins and auxins.
Soil conditioning and Soil Microbial Activity.
It is believed that seaweed extracts improve the water-holding characteristics of soils. They do this because alginic acid, which is contained within the seaweeds, combines with metallic radicals in the soil to form a polymer with greatly increased molecular weight. This also helps the formation of a crumb structure within the soil. It has also been mentioned that seaweed extracts may be useful in increasing existing soil microbial activity.
These microorganisms may secrete chemicals known as polyuronides, which are chemically similar to the soil conditioner alginic acid and help to stabilize the soil properties. Coupled with this, it has been shown that increasing soil microbial activity can be beneficial to grass colour, health and root mass. However, I must say that many newly established sand based rootzones, which are commonly used on both golf greens and sports pitches may contain limited soil microbial activity.
In research that I carried out, I found this out and the application of seaweed extracts in such situations as a means of increasing soil microbial activity may be of limited use since their purpose is to feed existing microbial communities.
Turfgrass Disease Control.
It has been shown that plants treated with seaweed products develop a resistance to pests and diseases. It is important to state clearly that this resistance is often quite limited and the use of chemical control is still required. However, seaweed extracts may be useful as a supplementary biological control factor in the race against pest and disease problems. The mechanism of this control is still unclear and some believe that the production of antibiotics from soil bacteria and fungi may be stimulated by the application of seaweed extract.
Seaweed Extract Application and Use.
In the past, seaweed extracts were applied very infrequently. In recent years, recommendations have changed and the product should be applied very regularly, at least on a bi-weekly basis if not more frequently. Many greenkeepers have asked me, when should I start applying the product?.
This question is difficult to answer because every situation is different. In grow-in situations, I feel that seaweed extract should be applied after germination, however in well established swards, application should commence well before the turfgrass will be under stress. The late winter, early spring is often recommended, although in situations where mild winters occur, some turfgrass managers apply the seaweed extract right throughout the winter period to condition the plants for the year ahead.
Seaweed extracts are not the solution to every turfgrass managers nutrition or stress problems. Will they ever replace traditional nutritional programmes?. I seriously doubt it. What is important to remember is that seaweed extracts were introduced into turfgrass as an environmentally friendly additive, not a replacement to traditional programmes. I feel that including a carefully selected seaweed extract in turfgrass management may be beneficial to many turfgrass professionals.
About the author
Tim Butler is currently studying for a doctorate degree in turfgrass nutrition at both University College Dublin, Ireland and Michigan State University, USA.
For further information contact Tim Butler at email@example.com
Gingell, S. 2001. A Taste of the Sea. Turfgrass Bulletin 213: 27-29.
Hall, B. 1998. Alternative soil amendments [Online]. Available at
Jensen, E. 2004. Fact or Fancy? [Online]. Available at
Lembi, C.A., and Waaland, J.R. 1988. Algae and agriculture. p.335-370. In: Metting, B., Rayburn, W.R. and Reynaud, P.A. (Eds.), Algae and Human Affairs. Cambridge University press, Cambridge.
Rhodes, D., and Hana, S. 1989. Amino acid metabolism in relation to osmotic adjustment in plant cells. p. 41-62. In: Cherry, J.H. (Ed.) Environmental Stress in Plants: Biochemical and Physiological Mechanisms, NATO ASI Series, volume G19. Springer-Verlag, Berlin.
Stephenson, W.A. 1968. Seaweed in Agriculture and Horticulture. Faber and Faber, London. 231pp.