Tropical Seagrass Mulch?

Hi All,
My plot is next to a beach. We're on the equator and have a bountiful supply of tropical seagrass washing up on our beach every high tide.
Is this good mulch, does it need washing first (our fresh water supply is very limited), and if it's used in compost does this constitute a high nitrogen or carbon component?

Many thanks for any help!

Hi Ian.

This depends on a number of things.

It could be good mulch. Is it sprayed much more than everything else by salt spray? If not, I wouldn't worry much. I know that the salt content isn't so high that it is dangerous for grazing, as salt marsh hay was an early staple for coastal pioneer farmers in North America. I would suspect that chopping some and letting it get rained on in a spot where that water won't go into the soil you're planting in would take care of anything adhering to the outside of the grass.

As to carbon versus nitrogen, it's relatively easy for growing things. If it's green, it's likely to be nitrogen-rich. If it's brown, it's likely to be a carbon resource. So if you let your green grass dry out, it becomes a carbon resource, hence the reference in composting to greens and browns as shorthand for nitrogen-rich and carbon-rich components.

Let us know how it goes, and good luck.

-CK

There should be no problem using it as mulch or using it for composting, one thing you would find advantageous as an amendment to the sandy area would be a bit of clay mixed into the garden beds.
Clay is sort of a magic bullet for sea side gardening since it allows your organic material to stick around longer than if it were used in just sand, it also slows the trickle through of water so your gardens will hold water better and as the plant roots grow, so will the holding ability of that soil.

As Chris brought up, fresh sea grass is a green and dried out sea grass is a brown, if you gather sea bird dung and add that to your heaped up sea grass, woo hoo!, you have the makings of a great compost that will be mineral rich as well.

Keep us up to date please, this will be very interesting and should work very well for you.

Redhawk

Many thanks both of you for taking the time to reply. I'll certainly follow your advice and give the seagrass a try, and leave it in an area at the back of the beach where it will get cleaned by the rain, but the salt will run back to the beach.

Our area designated for our farming/food forest is quite far above sea level, set back from the beach. It is already home to many wild fruit trees, and the soil is clay and covered in leaf mulch. We're not going to dig into the soil, we're focused on creating new soil on top. Mulching, chop-and-drop (especially of nitrogen-fixing ground cover) and composting our human-generated organic matter seems to be the recipe for this. Hopefully our plentiful sea-grass supply will add loads of new nutrients too.

Thank again!

Looking for seagrass mulch

Since I posted my original response, I have read several articles detailing how seagrass meadows are actually vast carbon sinks. I had thought this was pretty settled science.

The shocking part, for me anyways, was when a few of them went on to detail how seagrass was also instrumental in accumulating microplastics, along with larger bits, into underwater tumbleweed-like constructs that meet their ends onshore.

So the downside here is the potential for seagrasses to be a source of microplastics if you use them in your soil. I wouldn't be using them in compost or as mulch, personally.

But I would gather what washes ashore. I would probably, because of the plastic content, stack the bundles to dry out completely and then incinerate them at high heat in a retort designed to reburn the offgassed material from inside the retort. That way, the microplastics get incinerated at a high enough temperature and in absence of oxygen such that no dioxins are formed and the byproduct is heat, carbon dioxide, and some water vapour, not to mention the seagrass biomass will have been converted to activated charcoal, ready for composting or other biochar inoculation.

I would try to make sure the heat generated from the incineration went to some productive purpose, ideally. If it washed ashore regularly enough to stock a somewhat steady supply, I would probably look at power generation, or something that uses the heat more directly, keeping a heat-exchanger-based generator as a secondary process.

So while in actuality, we might want to be very careful with what we use as mulch, it could still be a useful source of biomass after pyrolysis, which does for soil microbiology and carbon what clay does for nutrient resources.

-CK