In other words, the dahlia you want to grow through the winter better be very irreplacable as it is hardly worth it.

Every year they either:
- become spindly and peter out and die (this in a room with a skylight!)
- get mildew and die
- shrivel up for no apparent reason and die

I think they just cannot get enough light or adequate air circulation indoors. If you have a greenhouse or sunporch I’d be more optimistic.

There's a lot of variables that decide whether they will grow or not. But start with this; Dahlias originate from Mexico and don't die completely back each year in the wild.

If you search through the forums for my threads from last year, you'll see the type of environment I created to over-winter growing Dahlias. My first attempt (last fall) ended miserably due to spider mites.

Regardless of pest or disease, you're going to have the simple problem of light. Assuming the soil is good, and you provide them sufficient (but meager) water, the only thing lacking is adequate light. Light of the right temperature, duration, and direction. This is why many find their Dahlias get tall and spindly inside...the Dahlias are reaching for better light.

I built cabinets that each had 4 x 4' 6500 degree Kelvin T5 flourescent bulbs ~12" above the plants (Bustan in Toronto can fix you up and they were great). Sunshine simply isn't going to cut it, it will simply tease the plant into thinking..."if only you could reach over here, or there..." and so they put their effort into growing tall and reaching.

Under sufficient lighting (which was on for 14-16 hours a day), they thrive. If you don't want them to get too big over winter, just give them less duration (but it must still be the right temperature light and close enough to them.)

If you were doing a single plant, you could easily do this on the window sill with a plant light over it and a timer on it. No need for cabinets and tons of lighting equipment like me. I was growing 100 plants inside.

Now to the problem I had last year, spider mites. I found a company in Stevensville, Ontario, who supply predatory mites. They have many to choose from, and they were extremely helpful in deciding which one I needed based on my environment and the spider mite type I had.

After my fall crop died, I cleaned everything, tossed all my soil, and almost all of my indoor plants. I bought new tubers and started from scratch in March this year. I didn't, however, realize that my Cannas, which were doing great, were haboring the spider mites. No noticable webbing or damage.

By the time my new Dahlias were getting to 3-4" tall, the spider mites re-appeared. I cut back my Cannas to get rid of the majority of the spider mites, and ordered the predators from NIC. They also recommended I grow a few pole bean plants near my Dahlias, as spider mites will prefer the pole bean to anything else apparently.

Well, one application of predators (essentially sprinkling them over all of the plants) and my spider mite problem disappeared.

I will be bringing many living Dahlias and Cannas in this fall to over-winter alive. My plan is to get predatory mites when I'm ready to bring in the plants, and will sprinkle them once inside to ensure I'm not allowing any I bring in to survive.

So, get yourself a plant light and go for it. With a plant light, there's no reason to think you can't make it bloom in the dead of winter, which would be lovely.

Cheers,
Russ