It's probally best to let them go dormant in the pot. Do not water. Then in March or earlier start watering, give high heat with a heat mat and lots of lights with a grow light. Use a humidifer.
You could do this all winter and keep them going but you'll have to keep them moist and above 65 degrees or they will stop growing. It just depends if it's worth it to you.
I let mine go dormant and try to start them growing in the house before I plant them outside.
I have never tried to keep them going all winter but I guess it can be done.

'Black Magic' and other Colocasias can be kept going under lights (and undoubtedly, in a bright window) during the winter - they just won't grow much. I've had several varieties including BM make it - they tend to look grungy but pick up and grow rapidly once outdoors in sunny, warm weather. Water when the soil in the pot is mostly dried out, and avoid using much fertilizer.
And you don't need to start with big plants in spring because of the quick pace of growth.

My 'Black Magic' (which is probably 'Black Runner' as both seem to be sold under the same name) has never survived going "dormant". The tuber always rots, even if I keep it dry. I have only been able to overwinter it by potting up small divisions and keeping them growing indoors over the winter. They aren't happy (and are extremely mite-prone) but they stay alive until spring when they can be planted out.

I have also been able to keep them semi-dormant (on the dry side, in a cool attic) but they never lose their leaves entirely, and don't form a large tuber.

I potted up a bunch of Black Runners last year to try to overwinter under grow lights. I didn't realize how wet they would need to be kept but treated them like my other normal houseplants. Most of the leaves dried up and the spider mites moved in big time. I ended up throwing them all away to keep the rest of my plants from getting infected.

Black Magic has very little in the way of a corm that will stand dry dormancy. I've never been able to keep them over that way like the old-fashioned EE. As long as you keep them slightly moist and a little on the cool side, they'll survive without much light. Of course the leaves die back, but generally the rhizomes will survive until spring.

I kept mine as a houseplant last year and am doing it again. I didn't have mite problems on this ( I did on some others) but they did get burned edges if they touched the frozen window glass. They have to make it 8 months inside here due to the zone- did fine. good luck. ( mine is the clump not running kind tho)
Karen

Just curious how wet you kept them.

Hey gang!

I wouldn't waste my time. I buy new ones each spring about 6" high and they get to about 7' !! Not worth all the hassle and then they die and fade away no matter what you do inside...

Try the grocery store taros next spring- i usually get about 7' out of them from a 3" tuber in March.

Good luck

Boca Joe

Here is a link that might be useful: Boca Joe' s Tropicals

I know that they are going to be trouble...I can see it already. Unfortunately mine didn't get that big until August (and I'm sure our growing season is a bit shorter than yours). That's why I figured that if I kept them alive over the winter I would already have a decent size plant by spring instead of starting from scratch. They are already looking quite droopy though. The ones you buy in the grocery store only grow green leaves, correct? I really like the black ones. Any idea where I could get those cheap. I had to pay quite a bit for these this year from a mail order company.

I planted 2 Black Magic E. Ears 3 years ago. This first
year they got about 6 feet tall, and had runners coming
all out onto the path,that they were bordering.
I mulched them with about 4 inches of Oak Leaves and Pine
needles, which had been ground up very fine. Last year I
was surprised to see 2 little babys coming up near
foundation of house. I trasplanted them and they got about
5 feet tall. Last Winter we had a hard freeze leaving 4
inches of ice for about a week. I knew that the E.Ears
wouldn't survive that.
I purchased a new Black Magic this Spring. It just
sat there until the weather started getting really warm.
About the time it started growing, and putting out new
leaves, last years batch started growing as well. So that
is 3 years the original has survived Winter. They are
about 4 feet tall now, and will be fertilized this week.
I imagine that by Fall they will agin be 5 or 6 feet
tall. They look really Fabulous paired with Little Blackie
Sweet Potato Vine, and Pink Futurity Cannas( Dark foliage)

I would just grow the black ones inside near a southern window as a houseplant. The traditional green ones I used to dig up and store like canna or gladiolus when I lived in a cooler climate.

If you want your Black Magic to get bigger before August, grow it as a marginal aquatic plant in FULL SUN. As soon as nighttime temps are above about 55 consistently, pot your plants up in a mixture of bagged topsoil mixed with sand. (Dom't use regular bagged potting mix) and place the container inside another sealed container of water, and you will have much faster growth. Fertilize every 2 weeks with a few Jobes or Miracle Grow houseplant spikes stuck down into the soil in the pot. ALmost all colocasias can be grown this way and will grow a lot bigger and better in cooler climates where they growing season starts later than they will planted as terrestrials

These are the ones that I overwintered as houseplants near a window.
Black Magic- kept moist- survived with some rotting and fewer leaves ea month- but survived.
portodora- looked great will do that again!
maccrorhiza- did ok as houseplant ..the one stored dormant died
esculenta- why bother- store dormant- too many spider mites on this type.
'lime zinger' xanthosoma- ok not an EE but can be done!

Hope this helps- winter (houseplant time) is long here- Oct to May.

Karen