Hi! I think that the temperature (and light) is a problem during the winter months since Coleus and Impatiens are tropical species. As temperatures drop, there is less uptake of water and nutrients, and excess water in the potting media give rise to fungal infections at the roots, especially with a lack of air circulation when brought indoors.

I root cuttings of my favourite varieties at the end of summer here and keep them above 20 degrees C/ 68 F in the house under on growing shelves that have a special light spectra for plants. It is better to take the seeds of Impatiens and store them in an envelope in a warm and dry area in a kitchen cabinet. For Coleus, take cuttings and get them rooted at the end of summer in a potting mix under cover, and provide as much light as possible after they are rooted in the winter. In Canada, I would put rooted Coleus in an unobstructed south-facing window if you have one. But don't try to root any annual successfully once the cool weather arrives and light diminishes.

Sounds more like too much water to me. Impatiens cuttings are renowned for rotting off in soil that doesn't drain well enough. I overwinter Impatiens in temperatures that rarely get above 70F and often go down to 50F at night. If you can keep to those temperatures then you can grow your Impatiens. Just no tto much water until they have really established good roots.

Thanks for the information. I have checked the temperature down there and with the lights on in the day it's 16C or about 61F. So maybe I need it warmer during the day. I don't have a vent down there from my furnance so should I use a space heater or a heat mat? I will also make sure they dry out between watering.