Is it best to over-winter some perennials - hens-and-chicks, astilbe, salvia, butterfly bush, ice-plant - or to plant in the ground for the winter?
I'm located about 20 miles north of NYC and able to keep the potted plants close to the house if that would help them over-winter.
If they are rated for your zone, I would leave them alone. I don't mulch anything ( I live in N.IL and our winters can be harsh some years ). If you have some perennials in pots, you can dig a hole & plant the pot with the plant in it. ..... something I learned about Hen & Chicks a few years ago : Don't try to protect them by putting them in the garage or house, etc. My hubby did that with a planter full of Hen & Chick and when I took them out of the garage in the Spring and we got another cold snap, it killed them. So now I let Nature take it's course. I only intervene if it's a extremely wet Spring. ~ Good Luck !
One thing to be aware of for cacti and succulents is that they can indeed rot if left out in torrential rain that is ongoing for more than a few days as it does not give the plant a chance to dry out and leaves it with wet feet - leading to rot. Good drainage is essential. Should you find any of your potted succulents or cacti waterlogged and you are fearing it is so bad that they will rot - a good measure to head this off is to tip them out of their pots, treat the roots with copper sulphate (from memory it looks like a blue powder and you can buy it at nurseries) and re-pot them back into clean dry potting mix. If the weather won't let up from the point of view of heavy and continual rain, move them under cover (but still outside if you can) for a couple of days till the weather settles. I used to keep cacti and succulents and many a cactus lived to fight another day after adopting these emergency measures! Succulents will cope with the cold better than most cacti as cacti hold more water and the water can freeze and split the plant as the water will expand.
If they are rated for your location to be in the ground it would be OK to plant them but make sure they are covered in mulch before the harsh weather comes. Something like succulents I'm not sure. You could call a reputable nursery (not a garden center of a big box store) and ask their advice. If a plant looks like it didn't make it come spring give it a chance. Often plants in dormancy look dead when in fact they are sleeping.if the roots are alive, the plant is alive. Give it a chance to show new growth.
I have found that my hens and chicks do best when I leave them outside and ignore them for the winter. When I bring them inside they kind of freak out and start growing abnormally. I have friends that grow them in bird baths and they flourish there. They tolerate the snow etc with no problems. There are other succulents that DO NOT do well outside but I can't remember what the group is.
Whether to bring your succulents inside to leave them out during the winter will depend on your weather and the plants. Some will over winter well such as theButterfly Bush and will only need to be trimmed back and mulch. Other more sensitive succulents such as the Echeveria, Agave, Aloe, Kalancoe and others will need to be taken inside out of the cold for them to survive. These plants should stay between 45°F & 55°F while they are kept inside. YourSempervivum can tolerate temperatures down to freezing but if you regularly get temps below freezing, take them inside for best protection. When preparing your Astilbefor the winter, be sure to cut them back to about 3-4 inches, taking care to remove all the foliage. The next step will be covering the roots with about 2 inches of mulch. Be sure to remove the mulch in the spring time when the weather warms up so you do not over heat the root system and cause decay. Many of the salvia can be mulched with 3-4 inches for best results as long as your temps only get into the teens. For the best results, check with your local nursery or go online and look up your particular salvia plant. Another option to over wintering your succulents so that you can avoid them getting really leggy during those low light winter months is to take cuttings from your favorite succulents and root the cuttings in a damp cactus mix. Keep your cuttings under a grow light or in a bright windowsill over the winter. Be sure to maintain a temperature between 45°F & 55°F for best results.