Phalaenopsis Journal Second Quarter 2014 | Page 22

The Myth of Curative Kelp
Linda Chalker-Scott, Ph.D.

Extension Horticulturist and Associate Professor
Puyallup Research and Extension Center, Washington State University

T

he Myth

Seaweeds are ancient relatives of terrestrial plants
and play a similar ecological role in coastal systems.
Kelps, the larger seaweeds species, are also of historical dietary and medicinal importance to various
human cultures. Their extracts have extensive industrial
applications, and more recently their activity as antioxidants and antibiotics has been investigated. It is clear that
human consumption of some seaweeds imparts health
benefits; can seaweeds also benefit plant health?
Vendors of natural garden products certainly want you
to think so. Web sites and sales literature praise the effectiveness of seaweed extracts as soil conditioners, disease
suppressants, and stress reducers. Research (rarely verifiable) is presented to support the use of seaweed drenches
or sprays on turf, fruits and vegetables, flowers, perennials, shrubs and trees in every possible situation. Are seaweed extracts that elusive magic bullet for creating perfect landscapes?

1) Rooting
Logic suggests that the growth regulators found in SE,
like any other commercially available rooting hormone,
can stimulate root development on cuttings and transplants. This suggestion is borne out in research on both
potatoes and pines in laboratory and greenhouse applications and could have use as a root dip during transplanting. Success would not be expected (nor has been found)
in field applications to existing plants, as these compounds
are quickly degraded by microbes and are unlikely to have
any regulatory effect on nearby plant tissues.

2) Turf health
There has been some success in utilizing seaweed extracts as a turf-enhancing treatment. The predominant
research has focused on Kentucky bluegrass, where SE
applications have been associated with improved seedling
establishment, rooting, and increased drought and salinity tolerance. However, other research with the same plant
material reported “little effect” after SE treatment. SeaThe Reality
Seaweed extracts (SE) have been dubbed “biostimu- weed extracts are also reported to improve root growth of
lants” or “metabolic enhancers”, defined as chemicals bentgrass and improve the “physical strength” of environwith growth-enhancing properties but little nutrient mentally stressed turf.
value. Growth enhancement has been attributed to the 3) Foliar growth
presence of plant growth regulators (sometimes called
Other than the aforementioned turf benefits, there are
plant hormones), and several of these growth regulators few, if any documented advantages of SE application to
have been isolated from seaweed extracts, including cy- plant foliage. Treatment of cabbage resulted in no change
tokinins, auxins, and gibberellins. This is not surprising, in either head yield or nutrient content; similarly in apple
as seaweeds are part of the plant kingdom and like other neither vegetative growth nor leaf mineral content were
plants manufacture their own growth regulators. More altered. Likewise, SE did not improve production of pepimportant is the question of whether these substances ap- pers or several species of herbaceous perennials.
plied to other plant materials might have similar regulatory effects.
4) Fruit size, yield and/or quality
Many studies have examined SE efficacy in impr