Indoor growth

Hi everyone!

I have been growing Lithops indoors for almost a year now; both seedlings and adult plants. From what I have gathered, Lithops seem to be very slow growing plants.Despite this, I worry mine might be growing too slowly. I was wondering if anyone else on this sub has had success with indoor growth for long-term specimens (3 or more years of age).

Some questions.

Does heat have a positive impact on their growth?

How do you provide heat if necessary?

What grow lights do you use, with what PPFD?

I live in the Northern Hemisphere. Winters here are long and frigid with temperatures of 20–30 degrees Fahrenheit, while Summers are usually humid and 85–90 degrees.

Here are some photos of my 8 month old seedlings that have finished their first splits for fun!! When I mention mine growing too slowing; it is mostly in regard to my adult plants which I can always expand upon more.