They are a common outdoor plant in southern CA, but they are a bush form not a tree as you say yours is. They are usually 4-6 feet. My gardening book says they lose their leaves at 10 degrees and are killed to the ground at 5 degrees, so I don't know if it would work for you outside or not.

Your plant is so small; I wonder if it is a small variety. Is it potbound? You could pot it up and it might grow bigger. I never thought of nandina as a houseplant. They are nice plants.

Don't know if I answered your question, but that's my 2 cents.

Toni, it is a fairly common shrub here. The older form, Nandina domestica, grows about 4 to 6 feet tall. There are numerous hybrids, many of which max out at 3, 2, or even 1 foot tall. They were very popular sellers at the garden center where I used to work, and I see them in commercial landscapes a lot. I put one in a year ago in a sheltered spot in my yard and it is doing well.

You do get significant damage/dieback at the temps that socks listed. We had a rough winter this past year, and a lot of the more exposed ones had a great deal of ugly dieback.

It's listed as hardy down to zone 6 or 7 - you'd really be pushing your luck to have it outdoors all year where you are.

I agree about a larger pot, though.

I hope someone from your zone steps forward to help you with your problem. Your plant might survive in your area, but most likely will die to the ground in winter. (I'm shooting from the hip here) In my area, zone 7, this plant, according to the variety, will grow anywhere from about 2 feet to 6 feet or more with beautiful red berries. Some varieties also have other color berries. If you have a local Extension Service, they might be able to help you. Good luck.
Bill

Thanks, everyone for your help..But perhaps I should have been more specific..I haven't any intention of leaving Nandina outside during winter months..
Even though the site I visited, accents, sold them as perrenials, I'm sure it was meant for higher zones..I did some reading on this plant, and found they grow as trees in CA. But never here in IL>>LOL.
I was just asking if anyone knew how to grow in a container, and if so, what type of fertiilzer is best..also, wanted to know why it's still small..Since I've had it, can't recall exact yrs, but got at a nursery in HI for 1.98, it's grown maybe three times its size since receiving it.
I don't think it's rootbound, but will check today. I also had the green variety but it died last winter..The purple is doing fine though..just a very slow-grower..Also, what type of light do those that grow in CA get? Are they in direct sun? med, shady spots? Seems to me since the leaves are thin, it wouldn't adapt to bright light..it's in a south window, but behind taller plants, but still gets a good amount of sun. Foliage remains purple..it's never flowered or berried..I really like this plant and would love to see it grow taller.
BTW, Socks, I've pruned the bottom so it's tree-like, (not the top or sides) Thanks again, Toni

They can take full sun or part shade when used outdoors. I imagine it can take as much sun as you can give it indoors. More sun might help it grow faster and perhaps bloom, but it's not a fast grower anyway. Perhaps flowers outdoors are triggered by the cold winters or day-length in the spring?

I use MiracleGro fertilizer on mine and it seems fine.

I didn't think you were planning on leaving it outdoors but wanted to mention just in case.

There are several cultivars of Nandina. Perhaps you have one of the numerous dwarf varieties. All of those with colored foliage are dwarf, as far as I know.

The species, Nandina domestica, is a vigorous, fast growing plant. If grown in a fast draining, coarse textured potting mix, it should be several feet tall by now.

Inside, these plants should be given as much sunlight as you can find, but protect it when you place it outdoors for the summer. When grown outside, they are very happy to be in the full sunlight and obtain their best color there. They are not fragile plants at all...but growing them inside will make them more so.

Most of the dwarf cultivars do not form berries.

Thanks guys..does anyone know how tall a dwarf grows? Actually I'd be happy w/a 3-4' tree, instead of a 10'..LOL..
Today, Fri, is my big house cleaning day, but I'm going to make time to unpot the Nandina, and check its roots..
Got the Nandina at a place called Packers Nursery in HI..He used to sell 'x' amount of plants, but never was anywhere as large as most nurseries..to be honest, don't know how he stays in business..He used to specialize in Plumerias but there's nary a one for sale..in fact, he's only got 3 plants for sale..LOL..coffee, red ginger, and ponytail palm..each plant goes for 1.99, minimum 5 plants..
I've yet to take plants out, except for a few, because of millions of Cicadas..they're everywhere...I watched the video of their short lives, which is sad..but one thing they do is peel bark on trunks to lay eggs..I fear they might peel my citrus or other plants w/trunks..They particularly seek small trees.
I'll also try a fertilizer to see what happens..Because of its slow growth, I fear fertilizing too much..I believe slow growing plants should get very little food...But that's just my opinion..
Anyway, thanks again..Toni