Red alder in the garden

I've been transplanting these guys around my property for years, they're a great free resource of firewood, a quick privacy screen, leaves in the chicken run etc
Last year I planted a few in the garden, about 2 ' tall. I'm thinking that they'll be a benefit by fixing nitrogen, give a bit of shade, build the soil, etc people look at me like I'm crazy when I tell them this? Am I nuts? Would there be any downside? My thinking is I can always drop them in a few years and chip em.
I not noticed that of the two white walnuts I planted about 5 years ago, the one that's surrounded by alders is 3 or 4x as tall. I thought maybe the extra nitrogen had something to do with that
Any thoughts?

They are apparently good for coppice, so they might be hard to kill off later.
Tree roots can aggressively invade garden beds,out competing the annuals.
Some nitrogen fixers are said to do little or no fixing of nitrogen is already available, so you might not get the benifits you want.

All that said, I build raised lasagna beds right next to fruit trees.
I feed the bed annually and get no  tree roots in the annual root zones.

In your posit, I would plan on pollarding them annually,  or even continuously.

Thanks,  I guess there's better ways to add nitrogen and provide shade.

Mike, I am doing this as well, so I think it is a good idea. The annual pulsing of roots and leaf biomass decomposing does improve soil, hence the ability of later succession trees to grow where they could not before alders’ help. I think if in a place with decent soil already and minimal sun it may be less helpful, but where I am using them I have very poor soil to start with and plenty of sun and wind for the alders to help moderate.

The above post points out a good reason not to waste nitrogen fertilizer on beds around the alder, but I do not see a reason not to try this. If they grow back from coppice, then just keep cutting them back and get a proportional amount of root die back which will decompose in place, fertilizing the soil. I use the trunks and branches as trellises too.

Ben, exactly what I'm thinking.  I cut them back every couple of years, they won't take over. We get alot of sun in the summer , sunrise to set is 16 hrs right now, much of the garden gets too much afternoon sun in the summer. If they're causing a problem I get rid of it. I've had issues of plants going yellow and not growing so I'm thinking nitrogen is an issue. Comfrey tea helps but doesn't solve the problem

I don't think of Red Alders as coppicing easily. I've probably seen some suckering from roots. But, no, when they fall over they tend to be dead and done. Granted, I am thinking of trees that were already well grown 30 years ago when I was a boy and first got to know them. Younger ones could be different. But I can't think of one that came back after we cut it, either.

Are they yellowing on older leaves, younger leaves, or both relatively equally? If you cut back alder branches, does this seem to help with yellowing? If it does help, it may be due to nitrogen released with proportional root die back by the alders (most plants balance their root to aboveground growth).

Sounds like you are at a pretty high latitude, whereabouts are you? It can help us bring  some context to our answers if a general location, elevation, and annual precipitation is in your profile or signature.

I’d echo Jeremy’s comment on red alder coppicing, as it does seem the whole trunk dies when losing their leader. The do handle thinning lower branches well though, as they do naturally when any given leaf or branch does not get adequate light (6hrs+).

The yellowing is on my plants in the garden. The alders transplant no problem. The ones in the garden are young,  I'd probably chop them when they're 10' or so. There's no real plan though, if everything around it dies, I'll cut it. If they thrive, I'll leave it. I like to experiment.

I didnt mean to discourage your plan at all, rather quite the opposite!
My experience with coppicing/pollarding black locust   catalpa and mulberry made me warn about the potential difficulty of terminating such a tree.
I have no direct experience with alder of any kind, but a quick google indicated they were good for coppice.
That suggests they will grow back from stumps,which could be good or bad, depending on the scenario.
The source I read also said to coppice on a relatively short cycle, as trees cut at older than 10 years would not readly grow back.
If black locust is any indication of how nitrogen fixing trees grow,  a 10 + year old alder could be huge.
I chop down one particular black locust sapling every year, and t grows back strong every  year.
Based on this I have started siberian pea shrub cuttings in my tomato and cucumber beds  but NOT black locust.

Alder is clearly not locust, but it may still ressist dying on cue.

Thanks for the clarification William, but I did see some wisdom in your post regardless.

As for the yellowing leaves, older leaves vs younger leaves yellowing on the same plant indicate different things. Older leaves naturally yellow as the die off, but can indicate N deficiency if it is premature. In some cases N can be locked out by PH out of the tolerable range for that plant. If its the whole plant yellowing, it could be a temperature issue or over/under watering. If on tips of upper leaves most exposed to sun, it could be sun-scald. Regardless, I would likely not blame the alder, though it may not be performing the miracle of immediate soil restoration/formation we hope for. I might experiment with thinning lower alder branches in an experimental intervention vs control (no thinning) setup to see if that alters the yellowing issue. Maybe another intervention would be a really good compost top dressing or extract.

Well- here is some territory where I can throw my weight around.  After living in the tropics I got impressed by agroforestry, and then I started making my living and supporting my family with my agriculture so I had to GO PRO. Then I went back to the tropics, met Bill Mollison etc. etc. As I tend to get itchy and host polycultures of invertebrates on/in my body in the tropics I figured I might try to adapt some of the tactics to where I live (where there aren't so many bugs thirsting for my blood)
Cut to the chase: it works. But learn, observe and interact as uncle Bill advised. Ask local extension about what nitrogen fixing plants and trees work best where you are. Learn which are partnering with fungi and which with bacteria.
ANd examine your prejudices: "Scotch* Broom is a Plague! Witches ride brooms! We Burn witches! Burn the Broom! (which is Fire adapted- you'll "expand the stand" if you burn it, eh?)
I had an older friend also interested in Permaculture, a scientist (children's hearing specialist) He owned 20 acres along the Long Tom River in the Coast Range foothills west of Eugene, not far from Oregon Country Fair*.  Down at the Long Tom was an old log deck where the previous owner had piled logs  'way back when, to float them to the mill in Junction City
*(if any of y'all want to experience the Fair in it's fullest, lemme know ASAP and I'll see if I can hook you up with the non-profit information/education area called Energy Park: you can't sell stuff but you can pass out information on the educational programs & etc.) It's where I cut my teeth on selling Permaculture. It would mean more or less a week of your life, some bucks, meeting a zillion interesting people, even hallucinations (at the Fair you don't need drugs to hallucinate) And it's no exaggeration: Tribes were living there for millenia before they got shuffled off. The Beavers are back at least.) SO: at this square of bladed-off subsoil Curtin Mitchell decided to plant an orchard: an acre of : (drum roll) SCOTS BROOM! Curtin decided to experiment: he divided the plot in two, cleared the broom off one half, and merely cut a pattern of holes in the other, and planted Apple rootstock on a grid in the whole of it. by the time three years had passed, the apples IN THE BROOM were bigger and happier BY FAR. So what do you think?  I thought I should explore Broom culture. I now plant any suitable nitrogen fixing plants in any system I disturb, and I also cut suitable "broom sticks" anywhere I see broom growing, because I had one sprout up at one of the first ponds I built after I discovered permaculture: the farm tractor ran the baby over so it was crooked in 3 years it was big enough to make an interesting cane. So I cut it and seasoned it, barked it and sanded and oiled it. I hardly ever used it. But my father was a polio survivor and altho he was a poster child for surviving polio, by 60 he couldn't walk very well, especially after driving across the country for days w/o exercise. He asked me: "Do you happen to have a cane?" He used it the rest of his life. I have it back now, and I make canes with broom all the time. 1) no one will get mad at you for cutting broom in a National Forest (or wherever) 2) for a legume, it's not very heavy, but still quite strong, and I like the resilience, which translates to more vibratory information about the ground traveling to your body thru your hands. 3) everyone is legally entitled to have a cane or walking stick: around the world there are cases of warrior societies being conquered by stronger empires: there's an Irish song from World War I about having a walk down 'round the harbor and the English recruiter who finds them and pitches them to enlist for the King to fight the Kaiser: the song ends with the recruiter being battered and bloody and running for his life.

Alder is a natural cover crop that can come up as thick as grass where it is native.  In North Maine I was describing how we would log alder for furniture like they did birch.  He could not believe it but there it could only grow from May to September while here it grows from February to November so some become dominant before others shade them out.  Scotch Broom was imported here initially to an area indigenously maintained as prairie where it out preformed alder and now competes with it through out  the area.  
   If you are cultivating and weeding an area consider their utility for your circumstances.   If you neglect the area Himalayan black berries may shade them both out.

There are lots of Alder species. Some tend to grow with a single trunk, some as multi-trunked big bushes. Some coppice, others don't. I am especially sweet on Italian Alder- (well I DO live in a moist Mediterranean-type climate. Italian Alder is heat tolerant and this year has shown that if you can't take heat this might not be the place for you.) Italian Alder has shiny big leaves, can grow in heat, tolerates hard clay soil (check!) And it coppices. I first saw the tree in the Central Valley of Cali, at a highway rest area. In the NW, and  into Canada, Black Alder is the common streamside Alder. Could it be that being multi-trunked and sprouting readily/coppicing might be a way of coexisting with Beavers? I have done plenty of outdoor cooking with Alder, and it works well. Burns steady and the smoke imparts a good flavor. The leafy branches can be used in layers in a pit oven, they lie pretty flat. The small multi-trunked Black Alder is favored for specialty charcoal in England according to the BTCV* Charcoal handbook. Since the 1980's I've been planting alders, starting because I wanted the nitrogen fixation for my bamboo nursery. It worked pretty well. I have found that some people are a bit confused that a person might plant trees to develop soil instead of rePEAtedly planting peas or soybeans and driving a tiller all around until their hearing is as bad as a Tavern Rock Band's ears. And, yes I do plant tree Legumes too; I LOVE black locust and forgive it it's thorns.

*BRITISH TRUST FOR CONSERVATION VOLUNTEERS- The hand book series, last I knew, is now available primarily online: good to have in your library.