2 Answers

A coleus plant is hardy, able to survive in both a container indoors and in the soil outside. However, being a warm weather loving plant, it will not survive a harsh, cold winter. When the weather begins to turn cold you will need to take some precautions to ensure a healthy coleus in the spring.

Bring It Indoors

For starters if you have your plants outside, then transplanting indoors will save your plants from freezing. Carefully dig around the plant and lift out of the soil. Transplant it into a pot with soil that is already moist.

Cut It Back

When the weather begins to drop, especially at night, cutting back the coleus flowers will help the plant conserve a lot of energy, and food. You do not have to worry about hurting the plant too much if you cut it back too far. Coleus is a very hardy plant and can handle the cutting. In fact, it will come back even bushier and more colorful than before.

Cover At Night

If you live in an area that does not get below 50 or even 45 degrees in the winter time, then you will only need to place a small covering over them to keep the chill off the flowers and leaves. Remove the covering in the morning and let it get full sun.

Read more: http://www.doityourself.com/stry/winter-care-tips-for-your-coleus#.UMURR5thHFo#ixzz2Eb3YNtk6

in the u k they are mainly used as indoor plants but over the last 10 -15 years we have used them as summer bedding outside but at the first sign of frost they are gone,so in answer to your question they are happy down to about +5 c,any lower and they`ve had it.