Gardeners are often looking for fertilizer that effectively supplies nutrients to the plants in their garden, is good for the environment and is not harmful to pets or other animals in the yard. One organic kind of fertilizer many gardeners have turned to is seaweed, a kind of algae that floats in the ocean.
The evolution of seaweed is difficult to know because seaweed lacks structures that resist deterioration, and left no fossils. Seaweed is considered a form of algae, but is the most complex kind of algae that exists. The plants float on the surface of the ocean because they have structures that fill with gas, according to Michigan State University Extension. Seaweed can be very different from land plants, containing completely different kinds of chloroplasts and producing different kinds of stored food.
Seaweed often washes up on the shore, where it can be collected. This seaweed is composted like any other organic waste. When the seaweed has sufficiently broken down, it is added into the soil about six months before the intended plants are added to the soil in order to give the seaweed adequate time to become integrated with the soil so its nutrients can easily be taken up into the plant's roots. This seaweed can also be purchased in a liquid form, often combined with fish emulsion.
Seaweed contains the primary nutrients that plants need in order to thrive--nitrogen, potassium and phosphorus. Seaweed holds moisture well, which keeps the moisture available to be absorbed by the plant's roots. The seaweed also acts as a food for bacteria that effectively break down nutrients in the soil. Material that is more broken down is easier for plants to absorb. Seaweed contains nutrients that are in the form of special starches that cannot be absorbed by the plant, but bacteria near the plant's roots are able to break down these starches so they can be collected by the plant.
Liquid seaweed fertilizer is another form with a low amount of nitrogen so it does not burn the plant with excessive nitrogen. The seaweed can come as kelp meal, which is mixed into the soil. All-purpose seaweed has other chemicals that increase the availability of nitrogen, potassium and phosphorus to the plant.
Seaweed can sometimes have insufficient levels of nutrients for the plants, causing a deficiency of nitrogen, potassium and phosphorus if the seaweed is the only fertilizer that is used. This fertilizer is often used as a supplemental fertilizer.