The seeds are probably no good. Sugar maple seeds usually sprout roots in 60 to 90 days. They should be collected in the Fall as they ripen in Sept/Oct. and stratified about this time of year so they start rooting as the warm weather arrives.

The heat mat should be fine once the seed has germinated but without a thermostat the mats can become too hot for some living things. Best to monitor the temperatures to make sure what's going on. Low to Mid 70's would be about right.

Sugar maple seeds shouldn't need scarifying but maybe 2 year old seeds will become too hard to absorb water and may benefit from this.

Six months is an awfully long time to have seeds wrapped in moist paper towels in the fridge. Could be some type of mold started up and destroyed the seeds over that time.

Bill,

Thanks for the tip. I read somewhere that seeds could be viable for years, if stored in a cool & dark location. But if I'm understanding you correctly, you're suggesting my seeds went bad after two years?

As for the scarification period, I can't seem to get a straight answer from any source online.

From what I read, it can range anywhere from 90 - 180 days, depending on your source. My source is this : https://www.google.ca/amp/s/m.wikihow.com/Germinate-Maple-Tree-Seeds%3famp=1

I plan on ordering more seeds. I really want to get this off the ground. :)

Maple seeds germinate best when harvested and planted while still green and soft. (Of course, you don't do this before they have sized up fully). When picked instead after they become hard and brown then they have a full dormancy that has to be overcome. Which is what you have been trying to do.

The purpose of this dormancy is to prevent the seeds from sprouting at a dumb time, like the middle of winter. So when a particular kind of seed is known to need alternating hot and cold periods to sprout what is being done is duplication of the passing of seasons, starting from when the seeds would drop to the ground during autumn in nature.

If a kind of plant has seeds that sprout a root first and then a shoot later, during a different season then it may take quite awhile for them to be ready to be potted on. Also there are some kinds where different seeds from the same batch sprout at different times, perhaps over a period of several years. Again this will function as a safeguard, in this case assuring that if a given year turns out to have some killing event like severe cold or drought the entire generation is not lost to it.

@Embothrium

The seeds I ordered were (fairly) hard; definitely not "green and soft". I guess that's because I ordered them online. No way around this for me, as I have zero interest in manually collecting seeds.

What about my inquiry regarding the Dremel tool? Any thoughts on this?

I guess I'l just have to keep on trying.

Your article talks about several different species of maples so you have to be careful to make sure the information you're reading is about sugar maples.

Here is a link About sugar maple seed that is easier to understand.

Let us know how you come out. :-)