The benefits of seaweed extracts have been known to growers for thousands of years, but only in modern times have their active ingredients been identified. Seaweed extracts are rich in natural plant growth hormones and beneficial trace elements, and they are a component of most biostimulant products found on the market today. The best seaweed extracts come from the brown seaweed Ascophyllum nodosum, harvested from mineral- rich waters such as those found near Norway and Nova Scotia. Ascophyllum nodosum grows in the tidal zone and is subject to extremes in temperature, flooding, drought, salt stress, and high levels of solar radiation and ultraviolet light. The seaweed extracts from these regions are very high in hormones and plant protection agents, and, when subject to stringent quality control procedures, are very stable products.
Seaweed extracts have high levels of plant growth hormones, especially auxins, cytokinins and gibberellins. Hormones are very small signal molecules that help steer the growth and development of the plant. Hormones are usually produced in one part of the plant and transferred to another part of the plant to initiate physiological changes. For example, auxins are produced in the leaves of plants then transferred to the roots and growing tips. Cytokinins, on the other hand, are produced in the roots and transferred to the leaves and growing tips. The balances between hormone levels determine their affects on plant development.
Auxins are best known for their positive effect on rooting, and synthetic auxins are usually found in rooting powders and cloning gels. Only a small amount of auxins are needed to initiate root growth. Too much auxin, especially when applied to growing roots, can actually have the opposite affect and restrict root growth! Seaweed extracts contain small amounts of natural auxins and indoles that help stimulate rooting, which, when combined with cytokinins, result in the production of greater root mass. Greater root mass provides better uptake of water and minerals and a healthier and more stress-resistant plant.
Seaweed extracts are particularly rich in cytokinins. Cytokinins stimulate rapid cell division and the production of new cell walls, so cytokinens are particularly important for new growth. Cytokinins work in conjunction with other plant hormones. If, for example, cytokinins are applied during root formation, the cytokinins will stimulate the division of more root cells. If cytokinins are applied during the vegetative growth stage, the plants will grow faster with stronger cell walls. And if cytokinins are applied just prior to fruiting and flowering, more lateral buds will develop for better overall fruit production.
Seaweed extracts also contain gibberellins. Gibberellins are best known for their affects on stem elongation and flower development, but they are also important for breaking seed dormancy. Therefore, seaweed extracts are sometimes used to soak seeds before planting. The gibberellins stimulate the dormant seeds to produce enzymes that break down the stored starches into energy molecules needed for respiration. Marginal seeds, such as those that are a little too old, will have better germination rates when presoaked with seaweed extracts, and all seeds will tend to germinate faster.
When using seaweed extracts, it is very important to follow the dosage and application directions carefully. Seaweed extracts can be applied as a foliar spray or as an additive to the nutrient formula, but foliar application seems to be the most efficient. Just remember not to use it as a foliar spray on flowers. Also, be careful not to use too much! Hormones are very powerful, even in small amounts, and using too much will have the opposite affect on the plants. Too much auxin restricts root growth, too much gibberellin reduces germination rates, and too much cytokinin can burn leaves! Moderation is the key.