I know I've got lots of reading to do but perhaps some on would point me in the right direction.
I'm looking for nitrogen fixing plants for understory layers of a food forest as one might say. I'm in Zone 9, central Florida, sandy somewhat acidic soil. No slope really to use swales for catching water (water would only last a day before soaking away anyway) so I'm slaving away with drip irrigation to get things started. We usually have mild winters with only minimal rain, hot dray springs with almost no rain, hot humid late summer into fall with likely heavy rain.
So, how best to search for what types of plants to try and get?
Right now on top of my list is Southers Bayberry or wax myrtle (Myrica cerifera) -should be pretty easy to get.
Gumi (Elaeagnus multiflora) is also on my list but might be harder to find here.
I expect Pigeon Pea would also be good but zone 9 might get a little too cool for it to really do well.
Anyone have ideas of where to search for info on plants to help me find appropriate stuff for my location?
Great to have zone 9 represented! I love having a chance to nerd out on tropicals (well, sub-tropicals anyway). For starter I have attached a Nitrogen-Fixing Tree guide by Craig Elevitch written with Hawaii in mind. The publication is packed with good info and some species lists. Check out the hardiness of some of the upland species and some may be good for zone 9. However, these will probably be mostly overstory trees.
A couple of goodies to consider for the understory:
[li]Cycads! Yep, these gymnosperms fix nitrogen and hand handle shade. There is even a species called Dioon edule that produces nuts. Woo hoo![/li]
[li]Gunnera - Gunnera tinctoria is a crazy dinosaur looking plant that should do quite well in your area. It fixes nitrogen at the base of it's petioles. It has edible stems and, I've heard, the leaves have been use in cooking like corn or taro leaves are used in tamale making. The leaves are also used for roofing (although this would take a lot of plants to do). This one requires moisture.[/li]
[li]Groundnut - Apios americana should do it where you are as an n-fixer that can handle part shade. It does like moisture, though, so that would be a consideration to think about.[/li]
I'm sure there are more, but that's all I can come up with off the top of my head. If you can increase the ability of your soils to hold moisture through mulching and shading, you will increase your options. Along south edge where there is more light you might try a lot of different legumes, such as winged bean and lablab bean.
Of the ones I've listed, I would suggest the cycads as the best combo of drought and shade tolerance.
For starter I have attached a Nitrogen-Fixing Tree guide by Craig Elevitch written with Hawaii in mind. The publication is packed with good info and some species lists. Check out the hardiness of some of the upland species and some may be good for zone 9. However, these will probably be mostly overstory trees.
Did I miss it or did it not get attached?
Gunnera would be the only chop n dropper of that bunch, and only once it's established. Often the chop & drop method is used as an establishment strategy (release nitrogen, while giving light to the fruit trees). Many of those establishment n-fixers are intended to get shaded out down the road. For the understory n-fixers you put in later, I would probably just let them drop leaves on their own. Hopefully, you won't need to keep chopping and dropping once the system is mature.
Another thing to consider is overstory n-fixers. Lots of tropical NFTs grow to be huge, but they cast an umbrella like canopy of light, dappled shade (good example include guanacastes and monkey pods). If these are spaced throughout the entire forest they can provide nitrogen & light shade while still allowing other things to grow. For zone 9 I would look into carobs & tamarinds. I'm not sure about their hardiness or height, but it would be worth researching.
Right now I am looking for those early stage nitrogen fixers that are used during establishment of such a system since I am still building the soil and the chop and drop method seemed a far more sustainable way to build soil than simply hauling in organic matter and fertilizers.
What I really need is a good way to search for the appropriate type of plants. So far I have not found any very efficient ways to search.
One real problem in those hot places is how fast the sun breaks down the organic matter! I lived in Las Vegas, NV, and had the same problem.
You might try the Plants for a Future database http://www.ibiblio.org/pfaf/D_search.html#USE and under Other Use, highlight BIOMASS and submit. Oddly, they don't have nitrogen source as a choice, but it's British, so.... you know...
If you're going to try Gunnera, it needs a LOT of water, esp in sandy soil. I have sandy loam here in WA, and have a hard time keeping mine wet enough. I hope to be able to move it and then direct greywater into a basin beside it. Eventually. Could you direct rainwater to it via a roof gutter pipe or something?
Thanks for the link, I'll have to go check it out.
I'm not searching for sources of some of the larger/longer lived nitrogen fixers, especially ones that can handle the chop and drop or use as some sort of bio-mass or fodder crop.
I'm gonna check out the biosphere nursery when I'm out and about today. Unfortunately their plant list doesn't seem to contain many if any of the plants I'm searching for. I'll still try them though their focus seems to be xeriscape plants and scrub land restoration and some aquatic and bog land restoration.
Hopefully some one there can be of more help than their web site seems to be.