What are the cuttings of? Some things can just slow down when it's cold and it's OK. Some things can benefit from it being a bit warmer.

I have most of my plants in a relatively cool spot, and find the heat mats work well for rooting cuttings. Geraniums and salvias are two things which seem to root much better with the bottom heat yet struggle elsewhere. If its already a warm spot I’m not sure I’d bother.

"What are the cuttings of? "

Heliotrope and a few varieties of salvia.

Mmm, I don't bother with extra heat or light - seeds get planted when I get around to it and the seeds germinate and grow away when conditions trigger awakening from dormancy...eventually. The pros of this - utterly effortless and carefree. There are cons though. Heat and light controls are really useful for places with short, intense growing seasons. Bell peppers and onions from seed need a long growing period so really benefit from an early January start and extra help in the form of light and warmth.

Mostly though, I grow a mix of easy annuals and vegetables along with hardy perennials. For the perennials, I don't feel under any pressure to kickstart growth - often I won't see blooms until year 2, 3 or 4 so I just let them get on with it in their own time. I can't really think of any annuals I am planning, which are going to need extra help...but sometimes, even my best plans go awry. On the whole, it suits me to keep my gardening as simple and lo-tech as possible, with plants which are resilient and adaptable to survive my uncertain horticultural attempts.

I realise that I have not answered your query at all, mxk3 - just rambled on irrelevantly (as usual). I would go along with your feeling that there is quite enough heat without requiring supplemental bottom heat.

I occasionally use heat mats for rooting cuttings of zinnias. And rooting hormones.

ZM

It would have been more accurate for my original question to be around transplants, not cuttings. These are mother plants that were grown from cuttings, about 2.5-3 months old. Regardless, they really liked it down in the basement under the lights on the heat mat, I saw some tiny threads of roots starting to poke through bottom of pots on a couple of them and very full, lush top growth - the top growth was looking good already since being grown in the windowsill, but they seemed to fill out more. I don't know if its the extra heat, the lights, the semi-regular fertilizing, or a combination of all of that, but dang they look great!

I have since taken cuttings from these and found the heat mat was much too much for the cuttings. I put them in plastic bags so they won't dry out, and since the air in the bags traps heat, I was concerned I was going to cook them rather than root them, so I removed the heat mat.

So it seems the heat mat is better for transplants rather than cuttings, if growing under lights.

I routinely have a heat mat under the plastic flat I use for rooting dormant wood fig cuttings. The cuttings share space with pots containing seeds that benefit from bottom heat for better germination.

I haven't run controls with fig cuttings that don't receive bottom heat, but my impression is that rooting is faster with the heat mat in place; soil temps probably reach the upper 70s before the mat which is on a timer shuts off at night.

With many perennials, warmish conditions are recommended for germination with cooler temps advised for growing on transplants, so I don't use heat mats at that point (there are a couple of fluorescent light fixtures available on the cool enclosed porch which stays in the mid-50s to low 60s in late winter and early spring).