A few days ago Angie and I quietly slipped away to one of our favorite seaweed stashes that we have discovered along the Rhode Island coastline. We wondered if Hurricane Sandy which had howled ashore last week had left a load of seaweed above the high water mark as is usually the case after extreme weather. I packed the truck with plastic muck buckets and a rake and drove to a stretch of beach along the Atlantic coast in the southern part of the state. There we found plenty of seaweed but, surprisingly, not as much as I had expected. I started filling the muck buckets, shaking out as much fine sand as I could, while Angie walked along the beach with her camera. I also tossed in some clam and quahog shells which come in handy for hardscape as well as a source of calcium for garden soil. The weather was ideal and my only companions were a few beachcombers walking by and a couple of testy seagulls fighting over little necks that they had grubbed out of the beach sand at low tide. It took me less than 30 minutes to fill the buckets and as Angie strolled back we headed off to lunch. It was a good day.
Like people, roses love seafood and seaweed is the seafood of choice for roses. Because Rhode Island’s major geographic feature is the magnificent Narragansett Bay, the smallest state in the union lays claim to over 400 miles of coastline. This explains why Rhode Island is called The Ocean State and with this much coastline, there is no shortage of seaweed which can be used as mulch, soil conditioner, and a winter cover for roses. Fresh seaweed does have its drawbacks though. Out of the water it smells like low tide and it will stink out the car if you leave it inside too long. But no worry, this strong seaside scent quickly dissipates outside.
So, why go to all this bother? Because, while seaweed is a low-analysis fertilizer, more or less equivalent to that of farm manure, it contains all the major and minor nutrients, as well as most of the trace elements, including manganese, iron, boron, zinc, copper, and a chelating agent known as mannitol, a simple sugar that makes nutrients already in the soil available to plants. And not only that, it is a teeming stew of micronutrients, hormones, vitamins, trace minerals, enzymes, amino acids, and growth stimulants which are directly available to plants.
When seaweed is added to garden soil, it conserves moisture and controls weeds but brings no weed seeds or plant diseases with it to the garden. University of Rhode Island researchers report that seaweed usage may result in increased plant resistance to mites and aphids and some diseases and maybe even to cold temperatures.
I first use fresh seaweed as a nutrient-rich winter cover and mulch, then turn it into the soil the following spring. It decomposes quickly, feeding soil microorganisms that, in turn, breakdown nutrients into forms that plants can absorb. As an organic amendment, it enhances the soil’s ability to hold moisture, helps prevent wide swings in pH, and improves the tilth of the soil. I also plan on adding some to this year’s compost pile increasing the nutrient value to the black gold without concern for weed seeds. While many gardeners are concerned with seaweed’s salt content, anecdotal evidence indicates no ill effects to the soil from salinity with moderate seaweed use.
Harvesting seaweed is easy. Just head to the beach with a rake and basket like we do and help yourself. In Rhode Island, it is not possible to be more than a 45-minute drive to the seashore from any point in the state. In fact, the Rhode Island constitution guarantees its citizens the right to gather seaweed from any public source. This harkens back to a century ago when seaweed was prized as an important agricultural product widely used on farms as well as home gardens.
In short, seaweed is an almost perfect organic soil amendment with the biggest drawback being availability. It does take a special effort for us to go to the shore occasionally to gather seaweed but visits to the ocean are always a treat and we usually make a day out of it. Regardless, when we’re done both the seagulls and I got the frutti di mare that we were looking for. Besides, as a New England gardener, what could be more fitting than using products from the ocean to make plants grow?
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