My favorite mulch plants have always been the most aggressive and "weedy: problem plants that i could find. Turning a problem into a solution. Capturing and harnessing what most people were scared to put back onto their
land and would consider obnoxious.
Of
course this approach has to have a method to the madness for it to work out properly. It could easily lead to more problems.
While living next to a very sensitive
native rainforest in Hawaii I quickly learned about what the nearby national park was using poisons to eradicate. These included a few varieties of Gingers, a small guava called "strawberry guava", a gnarly thorned himalayan raspberry, and a tree called Faya. These, among many other species, were all very quickly taking over the forest and displacing countless native species - dozens of which have already gone extinct.
After getting my
PDC I started looking at things much differently, and started coming up with my own less poisonous methods of dealing with the problem plants. i wanted to develop a system that could
feed humans, while also protecting and preserving the most vulnerable natives in our area. So I got a part time job as a "Forest Steward" for a nearby B&B, and started doing basic tree trimming and landscape maintenance for the community. I found a way to get paid to collect biodegradable resources, aka "green waste" and bring them back to my own place. The species mentioned above is what i would most often come home with.
I didn't have the money for any expensive machinery, such as a chipper/shredder or tub grinder, so that wasn't an option. Even if i did a lot of the material wasn't suitable to put through these machines, anyway. It was often too fibrous and too awkward to put into the feed. Larger logs i would chunk up into 2-3 ft lengths and stack them along my boundary where i needed a
fence to protect from invasive pigs. A fence is something i could not afford at about $10 per linear foot, but this wall of logs worked beautifully.
For the smaller more aggressive stuff i did have an area on my property that was a sizable low spot, which was a beautiful shape for a potential future
pond. I wasn't about to take the green waste to the dump, but i also had to be very careful where to put it, because most the these species were so aggressive that just throwing them on the ground would allow them to start growing and spreading again. The low spot was where i decided to start piling all the material.
After a couple of years of doing this the low spot turned into a high spot of decomposing materials being consistently smothered by new incoming material. The edges were sometimes a little problematic, but i would occasionally cut them back and strategically add material that wouldn't grow back in those spots. Eventually the pile got big enough that i couldn't reasonably add any more awkwardly shaped opportunistic materials, so i capped it off with
cardboard and less aggressive tree trimmings, small branches, leaves, cut grass, etc. Then i started a different pile in another spot while this one broke down and decomposed. Eventually i got
chickens and ducks, and they would start working the pile and pooping on it. Another year passed by and i was able to begin mining it. It turned into a fantastic composted "mulch", which if i was careful, rarely became problematic with the spread of overly aggressive plants.
As a side note - another big problem for this area in Hawaii is that there is almost no soil. Its basically lava rock everywhere.
So i was able to use a slow solution to convert an obnoxious problem into a major solution for my area. This pile of green waste ultimately helped me grow loads of bananas, taro, peruvian ground
apple, native Mamaki for tea, and much more, (very "hungry" plant species) without dependency on store bought fertilizers. Some of these crops even helped to bring an additional small income later on. But more often i would just share the surplus or use it to barter with when there was opportunities to do that.
My "mulch" came from obnoxious weeds.
To echo what others have mentioned above i think it is often less about selecting one or two favorite species to use for mulch, but rather using what is already abundantly available around you.
If i had to choose some favorites, though, then i would say grasses. They can be very well managed to feed the system in many ways. One person with a scythe, in the right context/situation, can get a ton of mulch material in a relatively short amount of time, while also having something to feed livestock - eventually converting greens into meat or
milk.
One of my favorite grasses is Vetiver. Its clumping, has a deep
root system, can also feed animals, and if left alone or forgotten - it doesn't become invasive. Even the seeds of some varieties are not normally viable. There are entire groups dedicated to this one grass due to its wide array of uses and benefits. The mulch is longer lasting, and very easy to harvest as needed.