How many years do you think it would take for a Ferocactus pilosus to grow from seed to say, 12 inches tall?

I'm new to growing cactus, and I just have no idea.

If it effects the growth rate: I live in Central Texas (zone 8b), and I'd like to plant it in the ground. I can give it protection in the winter.

You'd need to give it a lot of protection. You are a full zone out of what it is listed at 9b to 11, and 9b may be optimistic. This means that aside from cold protection you probably also need to be able to give it a lot of wet protection, which for in the ground plants can be hard. I have one that I put in the ground last fall and it did not like our winter that much, and we really did not have much of a winter. never once hit freezing. It will not take anything even close to what you just went through to kill that plant.

Growth rates are going to be dependent quite a bit on if you can get and keep the plant in its happy zone, if you can you can probably reach above average growth. I suspect that from a seedling to say 3-4 inches tall will not take that long, a few years or so, but then the next 8-9 inches are going to be when it will be quite slow and it may take you many many years to get it to 12 inches tall. These tend to get a little faster once they get to a certain size, but again growing conditions will matter a lot and if this cactus sees a lot of marginal conditions in winter it will probably influence its performance throughout the rest of the year.

I see the attraction of this particular barrel cactus, but my advice would be to go for something that isn't going to be quite so marginal to grow long term where you are at. There are a few barrels that would do better there.

Thanks, Mcvansoest.

Are there any barrels with some red color that you'd recommend?

It is tough, most barrels probably would really be pushing their cold hardiness by about a zone. Red spined ones are even harder, but you could think about F. cylindraceus (acanthodes), which generally is more yellow-orange spined, but it is highly variable and has some quite red spined varieties.

I suspect that your best bet might be Ferocactus hamathacanthus, that again has red spined varieties, though one should be warned that in most cacti with age spine color tends to go towards white/black/grey. Wetting the plant gets to have the color back on the spines for some until the water evaporates.

Both these are listed as zone 9a, but are also listed as being able to withstand short periods of down to -5 C, which would probably be in the low 20s F... and by short I mean a few hours at night, with day time temperatures well above freezing and dry.

If you end up growing these in the ground, you want to put them in a substrate (I am using that word intentionally, and I am specifically not using the word soil), that is raised above the surrounding area and consists mostly of pretty big rocks. you want to mix in just a little bit of soil but not very much.

I guess if you start these from seed you will be growing them in a pot for a while and I guess you can hope that as average temperatures keep going up that the winters become milder so that by the time you plant this in the ground you are maybe not quite so zone 8b anymore as the area currently still is.

If red spined is you main interest big cacti are going to be hard in your area. There are plenty of South American plants that can take a dry zone 8b, that also grow large but few that I can think of are going to have clearly red spines. One you might consider is Denmoza Rhodacantha - and I think it is listed as hardy in your area. It comes in orange-red spined varieties and with time they will grow to be several feet tall, but again by that size only the spines at the growth point are going to show clear color.