We used alder along with birch veneer plywood for cabinetry when birch cabinets were popular here. It resembles birch as far as graining, is slightly more darker or more of a red shade and is not as hard as birch. It was used primarily for the face frames and door frames/drawer fronts as it wasn't as pricy as birch, at least in them days. If you are going to stain it, i would say it would make a decent and reiable base, but if you are going to paint it, i would go with poplar as it is about the same hardness of alder but doesn't stain well. Poplar accepts paints very well.

I absolutely adore my alder cabinets but I don't think I'd use it on the baseboards. It's a little soft and every time you sweep or vacuum, you'll run the risk of dinging it up.

Thanks to both of you. It was the softness issue that I was worrying about.

I have alder throughout my house (millwork, cabinets, doors, etc) and have no issues with 'softness'. I find the grain resembles cherry more than the birch that sierraeast mentions. Alder is a little blotchy for staining without proper conditioning or pretreatment, but nothing compared to birch which is about as blotchy as they come (I have a strong bias against birch and maple because of this). Alder is certainly harder than MDF which is used quite commonly for painted baseboards. Don't sweat it. It's a great looking wood.

Hi Buzzsaw, I'm glad to see your post also. We have decided to build our exterior doors of knotty alder as, we think, the wood is so beautiful. We have a lot rough beams in our new build and cedar on our ceiling, all stained. This will be our first venture with alder so appreciate knowing it will need pretreatment to prevent blotching. We also have decided to go ahead with the alder on our window and door trim and the baseboard.
Do you have any pictures you would share of your alder in your home? Thanks, Jeanie