I recently purchased 11 Cactus plants in pots. Most are Mammillaria, Rebutia and Parodia cactus. Does anyone keep their Cactus plants indoors in the Fall/Winter? What are their Light requirements during Fall/Winter? I know watering should be very sparse.

Yes, I start bringing them indoors here when our outside overnight temps starts going 50F and below. I keep them dry, during the cold months, they go dormant. Indoors, they are positioned by my south facing window as light levels are shorter and less strong during winter.

Our Fall and Winter can be very rainy so it is imperative for them to be brought in. Cold and wet tandem is never good for them during the cold months, due to their growth slow down and dormancy.

The more light, the better. If you keep your indoor cacti at mild temps (room temperature during the day) and give them strong light (like right by an unobstructed south facing window) then you can water them the same year round. That is what I do with my indoor cacti. If it gets cold or there is not enough light, that's when you really want to dial back the water in winter. You can help induce dormancy by letting the plant go dry. Otherwise winter dormancy is completely optional for most cacti and not something you will generally observe under favorable conditions.

You can also augment with grow lights if there is not enough natural light indoors.

Ideally if temps indoors are sustained 65F to 80F which these cacti really like then occasional watering is okay, but we all know maintaining those heat levels is too expensive to do in winter, so just scale down watering or stop altogether, allow the plant to take its dormancy. Especially in January to Februrary when cold conditions are just much more pronounced.

I always think of it this way, these plants have their natural mechanism to adapt to weather situations, so we just have to adjust accordingly as the seasons demand it. Our indivdual micro climates varies, so you will have to observe them very well. Harder to reverse overwatering problems once the damage has occurred for them, since they are not naturally active during winter.

Sustained temps at 65-80F are not required to skip dormancy. Our outdoor temps get down to 45-50F during the coldest days of winter (warming up to about 65F in the daytime, reliably) and I continue watering the cacti the same as I would any other time of year.

The key is that the daytime temps reach near room temperature. It can get as cold as the range I mentioned without any need for adjustment in the watering schedule. Within that range a much more important consideration in winter is light, which is especially limiting because the sun reaches a lower angle in the sky. And when the light is low, you need to back off on the water.

We all have varying temperature goals indoors during winter, some would take it colder than most so the normal ideal room temperature is not often met. That is why caution in watering is very important during overwintering. So many cases of cold damage happens due to wrong timing of watering.

And as mentioned the light aspect, if there is not enough windows for natural light ideally on the south side, need to scale down watering or stop watering. But if grow lights are added, then it may help the plants settle in more comfortably to endure the cold season.

So Patrick, plan accordingly where you will position your plants when the time comes, and be very alert of the temperature changes in your area so you will be able to adjust your watering schedule according to the season. Our growing location is different, with our milder winter conditons, and yours is more northeast, much colder and more pronounced winter conditions.

Thank you all for your replies .

I will have a total of 17 potted cactus in the house. Right now, I have 6 on a table in front of my South-facing Picture window in the living room. The table has a Table lamp, and I am considering buying an Agro Grow lightbulb for the lamp.

Being here in New Jersey and having totally horrible rainy cool weather right now (which we have had since March) I can't put the cactus outdoors until we get a day full of sunshine. I have East, South, West, and North exposures around my home. East is good for giving my plants (roses and some Clematis) morning sun.
The front of the house is South-facing which is non-stop Sunshine. I have many potted Clematis growing on the front patio.

So, let me know your thoughts on getting a Grow lightbulb for the lamp.

Thanks.