Palm fronds as straw replacement?

Newbie here, but very interested and excited about possibilities. I am going to start building some small cob structures to test, but wanted to see if anyone had any theories or experience with straw alternatives in cob.

I am in Florida on the midwest coast, and the area I am planning to build in does not have an abundance of straw of any type. However, I do have an abundance of palm fronds! Structurally, these seem to be very solid and take forever to break down, as well as being very fibrous. Could this possibly work as an alternative?

My other thought would be the needlegrass (I dont know what it is actually called, but it grows in marshy areas and the end of it is so sharp it could take an eye out). I read in another post that silica content of the grass was a factor, and my assumption would be that since this lives in a sandy & brackish area, the silica content would naturally be very high.

Third thought is brazilian pepper tree. It is invasive, and I have acres of it at my disposal. Would this be safe to incorporate into a structure on some way, either as structural elements for a wattle and daub, or even within the cob itself?

I appreciate any help I can get! This is a remote location that is not accessible by machinery, so using what can easily be transported by a person or what is readily available in the area is very important to me.

Welcome to permies Emily!
Funny but I was just shredding yucca fibers to use in my next cob project. While I’ve never used palm fronds or the Florida plants that you mentioned specifically, I have used many fibers in freeform cob and adobe block construction and never had a problem in this dry climate. Usually (like today) I clean up the yard and gather dried or nearly dried plant matter for cob: Spanish broom, runner grasses, cactus, puncture vine, sisal from last year’s garden, narrow leaf yucca, and banana yucca. I avoid materials that are visibly rotting or have mold or fungus.
The big difference between using straw and thorny plants such as those I mentioned is that working with potentially-skin-puncturing material requires mixing with tools (wheelbarrow, hoe and shovel) rather than feet and a tarp. I wear cut-proof Kevlar gloves when handling mud filled with pokey plant trimmings.
Your idea to do some experiments with the plant matter and mud from your land makes lots of sense; people throughout time have made the most of what is most accessible.
Hopefully some Florida builders will respond to your question. Good luck and have fun experimenting.

Thank you, Amy!! This is really exciting news! Thank you so much for your response, I am even more excited to get out and do some experimenting now!

Straw is the stalk of a plant that has produced grains. The plant puts all it's energy into producing the grains, so most of what's left in the stalk is undigestible carbon. So when you're looking for an alternative, that's important to consider. You're looking for plants - or parts of plants - that have naturally died back, reabsorbing or using any nutritive value that could support mold or invite bugs to chew on it.

Think in terms of people picking herbs green and hanging them in a cool place so that the nutrients stay in the dry leaves. If I want to dry bamboo to use, I specifically leave the leaves on and leave it in enough light that the culm uses all it's nutrients to live as long as it can and dry out slowly, and then it will last longer as garden stakes or whatever I'd planned for it.

In my ecosystem, Bracken naturally dies back and would likely make an excellent straw replacement whereas nettles would need some help to get dry enough.  So I'd suggest you watch the life-cycles of the plants you're considering using so that you can choose a good time to harvest to use in cob.

I'd also consider researching historical uses of Indigenous people of the area. There were certainly types of sea-grass that was not only used for thatching in many places in the world, but much of that thatching lasted far longer than modern roofing does!

Definitely worth experimenting with!

Natives here lived in what are referred to as Chickee Huts, basically open air pole buildings with palm frond thatch roofs (kind of like what you picture a tiki hut to be). This was after early settlers drove them to marshy areas. Prior to being forced into a more transient lifestyle, it is believed they had a wattle and daub style homes, so I know it is possible to build those types of structures with local earth provided materials. I am not sure about the rushes, I rarely ever see any that are dried, so I would need to harvest some and see what happens. They seem to have something of a sponge like texture inside the hard exterior, I assume for filtration of the brackish water. Not sure how that would impact things over time, but I suspect it may have an interesting impact on the level of insulation the cob provides.

Such an interesting thread, I can't resist posting again.
Despite the fact that New Mexico’s climate is extremely dry and certainly very different from Florida and Pacific NW US, I will mention that I don’t actually let my material get so dry that it is brittle. I want the shear strength of the fibers and if the material gets too dry, it breaks. I also find that when adding super-dry material to mud, the two substances (mud and fiber) repel each other so it is more difficult to integrate. I have to add more water to the mix to make it work. Then I have to wait longer for the puddle adobe or cob to dry before adding courses. Historically, live but dormant (slightly “green”) turf was cut, flipped over, and stacked like bricks using mud mortar. This dormant turf method is similar to the sod house built by family in 19th century Nebraska. The roots are alive when stacking but die without air.
Speaking of air, because there are few air pockets in packed cob, the insulation value is low. I use cob for thermal mass (holding the temperature steady) and not for insulation.
For one experiment, make 2 bricks: one with fiber that is bendy, the other with brittle fiber. Dry them, then set up a drop test. Check the maximum height each brick can be dropped before breaking up entirely. If you do this, please let us know what happens, Emily.

Awesome!! This is such valuable information, thank you so much for your time and your incredibly thoughtful and educated responses!
I am going to be out on site this weekend, I will let you know how some of my testing goes!

I'm in SW FL and was thinking of a cob pallet shed with palm fronds instead of straw. I have also been looking for a permitted cob house in FL, I'm not sure if it's been done yet. Anyone know?

Any update on the experiment? I’m in Palm Springs , California . Palm is in abundance and would love to see what happens . I’m planning a con library for my backyard. If I can use Palm that will be great.

FROM; palm fronds used in unfired clay bricks

"Palm fronds and palms seeds increased the performance results of unfired clay bricks.
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Low concentrations of palm seeds and palm fronds produced strong unfired clay bricks."