I've never had them act as a perennial, however they will self-seed like crazy if left be in the fall. Once sowed in the garden, you'll always have them in your garden.

Don't waste indoor space, they are very easy to direct sow or wintersow.

Sharon

I agree with Sharon. I have had them act like a perennial though. The first year it only grew to 2 1/2-3', the next it got taller, and the stem became like a trunk. I ended up pulling out the old thick ones, which have a tap root, and letting the small ones take over. They do get rust so before you plant, put some cornmeal in the hole. Marg.

I agree with zebrina acting like an annual and self seeding, although last year I saw that they were selling it at our garden center as a perennial. I do find that in our zone 3 climate they need a head start so I start them with an clear plastic bottle over them. I cut the bottom out of liter pop bottles and set them into the ground a week or so before I plant to warm the ground and then I plant 3 seeds, take the lid off of the bottle. this acts like a clouch, When the seeds sprout I thin them to 1.

An alternate way is to cut a piece of row cover and put over the plot after you plant them. They transplant very easily