Hi Véronique, I'd agree with both Fermi and Arnold.
During the winter growing season mine live on a high shelf in the greenhouse to catch whatever light is available. They also enjoy deep pots, about one-third full of well-rotted leaf-mould (mainly oak & beech) with a sharp-drained mix above. This protects the corms against excess wet but allows the roots to run into the organic layer. Feeding at half strength also helps. Under my conditions seedlings still take several years (3-5) to reach flowering size but this might be speeded up by supplementary lighting as Arnold suggests.
