I can't imagine a pot Horsetail wouldn't look good in. I do prefer a gazed, foam, plastic pot that doesn't weep moisture. I've kept Horsetail in several climates (no serious freezing) in pots and it does fine. It does have a reputation for being invasive, good grower, etc... And that is kind of true. But not always. It can struggle too. It's not generally a plant it today and it turns into a prize winner next week type plant. I've always planted in clay soil. I generally don't fertilize the first year. Then not a lot. I don't like potting soil because I generally grow in a non draining pot and potting soil, compost, mulch and even top soil doesn't do well. In standing water you can even grow just in pea gravel but some fertilizer is needed. I like the clay because it can hold the water a long time if needed. Horsetail can take standing water but imo does better not in standing water. It can rot, not often, but can like when some other factor isn't great. Wet feet is fine and how I normally grow it. But the best possible conditions is still the same old well drain potting soil but watered often, like even a couple of times a day. That's way too much of a pain for me, so I like clay soil, no drainage, no standing water. Just easier. Even here in Phoenix I can not water for a week in summer when on a trip and it'll pull though. In San Jose CA 2,3,4 weeks without water was OK depending on the location (sun), pot and plant size.

Hi there. Thanks for your comment! I do keep them moist and they're in a southern window so they get lots of direct light. After talking to some more experienced gardeners, I think the most likely problem is that they're root bound. I'm going to use an auger to dig holes in the soil and fill them with fresh soil and see if that helps

Not sure where you are located (might have a bearing) but the common horsetail grown for containers, Equisetum hymale, is typically considered fully evergreen and is not cut back. In fact, it is the very vertical structure that gives this plant its winter container appeal. And they do not spread readily in containers....most sources suggest selecting a container to fit the plant as it is in its nursery container OR purchasing enough to fully fill your planter or container. btw, horsetail is NOT a grass - it is an ancient plant most closely related to ferns - and if being grown intentionally, it should ONLY be planted in a container due to its garden invasive nature.

Cram 'em in as close as you can! As noted in your previous post, they do not spread very readily in a container situation. And keep the soil consistently moist at all times