Does seaweed act as a growth stimulant?
Seaweed extract is being marketed and supposedly has special benefits when supplied with iron. The following comments are extracted from a gardening article on use of seaweed (there are various species of seaweed which may differ in composition that influences biostimulation). "Seaweed is a rootless plant in the Fucus family that floats freely or clings to rocks by holdfasts (root-like or disk shaped plant parts that attach seaweed to rocks but don’t absorb nutrients). Seaweed photosynthesizes the sunlight that reaches it through shallow water and it absorbs nutrients from sea water through its leaves. Since the ocean receives runoff from the entire earth, it contains all known minerals, trace elements, and vitamins. This primal supermarket supplies a more complete diet for sea plants than any plot of rich soil or fertilizer provides for land plants. Seaweed contains 60 or more minerals and several plant hormones. It is not however a complete fertilizer. It has a fair amount of nitrogen and potash, but very little phosphorus, a major plant nutrient.
Only a few seaweeds are harvested commercially. Norwegian kelp (Ascophyllum nodosum), a brown algae is the seaweed most used in gardening. Norwegian kelp is gathered off the coasts of England, Ireland, Norway, and both the Atlantic and Pacific coasts of North America where it is called rockweed. Gulfweed (Sargassum), a floating sea plant, is harvested off the coast of North Carolina. Giant kelp(Macrcystis) is collected in the Pacific Northwest.
Seaweed is constantly worn down by tides and eaten by fish, so it must grow rapidly to survive. Studies at the University of California showed that a frond of seaweed can grow a foot or more a day, given optimal conditions. The same growth hormones that prompt such rapid growth in seaweed , when applied to plants as a foliar spray, can increase the rate of cell division and elongation in those plants. The hormones also increase root growth when applied to the soil as meal or when seaweed extract is used as a root dip.
In recent turf tests at Virginia Polytechnic Institute in Blacksburg, plots sprayed with seaweed extract had 67% to 175% more roots than untreated plots. Plots treated in fall showed a 38% increase in spring growth over untreated plots and showed 52% more roots.
In tests at South Carolina’s Clemson University, seeds soaked in liquid seaweed extract showed rapid germination, and the resulting seedlings had increased root mass and stronger plant growth than seedlings from untreated seeds. They also had a higher survival rate. Soaking plant roots in seaweed extract reduces transplant shock and speeds root growth. Seaweed foliar sprays promote faster, stronger stem and leaf growth, and earlier blossoming and fruit set when sprayed on leaves and flower buds."