Yes, it is potentially invasive, but only locally, I think. Autumn Hill Nursery has a huge patch of it on the edge of their property in the front. It is most aggressive in wet areas.

If you want to look it up, the genus name is Equisetum .

Here is a link that might be useful: This might be the one

Would you agree that if I plant the 6X6 inch patch of rizomes that she is sharing with me INSIDE of a shallow plastic pot submerged in the ground with the upper edge just above the soil level that I will be ok with it not taking over the area over time.

My young children are fascinated with this plant and want us to grow it here. Actually they want to grow it and are old enough to know not to eat it or mess with it.

I just don't want it taking over the area that I plant it and I don't want to have to watch it every day to make sure it's not sprouting here and there.

Dora

You need to put it into something really strong. Mine escaped from plastic. They can either crack the pot as they get crowded or push up and escape over the lip. Mine are wandering around the front yard. I don't really mind them - just pull them up/break them off, and they've never gotten seriously out of control. But then it's a cottage garden, and horsetail emerging from a clump of lamb's ear doesn't sent me into hysterics. Some of the neighbors get freaked out, though. Why isn't each clump surrounded by a nice pile of mulch separating it from the next clump? Oh, and where's the grass?

So if I were you, I would get something stronger, maybe stone.

You need some sort of solid border that will go below ground at least 10 inches and above ground(or above your mulch)about 1 inch to contain their spread. Burying a large 2 gal plastic pot and leaving about an inch raised above mulch or soil will keep it neat. It still has the ability to through out runners and can spread from seed as well.

I had a large pot filled with Equisetum hyemale (the native one, that looks like bamboo) beside my pond and I became concerned that it would escape from the pot through the drainage holes, so I sat it on a large flat rock. During one especially dry summer, it didn't receive enough moisture and all of it died.
I decided that the two species of bamboo in the garden were enough of a threat to deal with, so I never replaced it, although I really liked the appearance of the stems.

I'm going to use something strong to contain them. My younger kids are just fascinated with this plant and them loving the gardening aspect is more important to me than not having something if the risk is low of it taking over my flowerbed.

I'll plant it to contain it above and below the ground and if it gets out of hand, I'll dig it up and share it with others.

It's been way too soggy here to get in the dirt outside so it will wait another week or two before I get it from my friend. Hers started about 3 years ago and she put it in a black plastic pot that a tree came in. She cut the top thrid off the pot and then submerged it into the ground, planted the horsetail in that pot and it has spread about 4 inches each way in the 3 years. The plastic pot was 18 inches and it isn't to the edge yet. Hers is planted in full sun and the area is dry, not moist. That's the same conditions I would have too.

I think one of the reasons that my kids are so fascinated with it is because the stalk looks like it could be used for a fantastic light sabre - they are obsessed with StarWars/CloneWars right now.

I'm thinking they would be different but also unique in an arrangement inside the house.

Thanks for the feedback from everyone.
Dora