No, apple seeds don't need us to germinate them indoors. Apple seeds need cold stratification to germinate. That means a period of cold generally followed by warm to break the hard seed coat and start the germination process. Conditions - weather, amount of moisture, the type of soil it falls on and how much soil covers it would all play a part in whether that seed will germinate and continue to grow.

Where your apple seed came from is hard to say - its quite likely it could have been birds or animals. I suppose its equally as likely that it came from someone eating an apple. It's always interesting to speculate how a tree or plant started growing somewhere when there was obviously no one planting it.

So, say it did come from your eating a store bought apple, which happened to have viable seed (not hybridized sterile seed), and that seed has grown into a sapling. Its hardiness and whether it will grow into a larger tree is yet to be determined. Young stock that has good snow cover all the way to its top may very well survive over winter just fine. As the tree gets larger the top will stick out of the snow and may die back every year. Whether it eventually fruits - well, you'll need to hang on to that summer house for several more years to find out.

How big is the sapling now?

Want to sprout apple seeds? Planting them outside in the fall works or if you put them in slightly moist peat moss right about now, in a closed plastic bag, in your fridge, about planting time you will have roots and a couple of green leaves ready to plant. The seeds need a few months of chilling to sprout.

If you don't want to wait a long time to taste the apples, they should be grafted to an existing tree or a fast maturing rootstock. Cold hardy rootstock may be needed in cold zones for the roots to survive the winters. The trees in question seem to be okay.

You will have mixed results. While some may be good or even excellent, some may be terrible.

If you have lots of space, growing new varieties of apples is a great way to add diversity to the cold zone gene pool.

Remember to chain saw all but the hardiest and/or best tasting.

If you do decide to chainsaw the apple trees, keep the kindling for an addition to your grill. Applewood place on the grill along with your food can add great flavor.

The key to growing apple trees is the stratification (or allowing the seed to winter) weather that be in your fridge or outside all winter is up to you. They need at least 2 months or more in cold temperature before they can be planted outside.

All good info here, ...most apple seedlings revert back to a crab apple.
Does it fruit? If the quality is not to your likings, birds will enjoy
them late in winter or early spring. Or it can be grafted over to
something desirable.

I know next to nothing about germinating apple seeds but I do remember when I was a child, my mom and I just planted an apple seed from a run-of-the-mill grocery store apple into a little container of dirt and it managed to germinate inside the house at room-temperature without any sort of special cold treatment. I can't remember how tall it grew inside the house as I don't think my attention span was too long back then....

YES...most apples are stored for very long time in just above
freezing temp. before they go to the store....enough for cold treatment.