I recently found a sprouted pip inside a Pink Lady apple. How can I grow a plant from it, preferably indoors? I live in a cool climate, in Scotland.
I would just like to grow the plant; I do not mind particularly whether it yields edible fruit.
If you try this, you will definitely not get "pink lady" apples, you will get something random, and you might have to wait 7 to 10 years before you get any fruit at all. Also apples grown from pips are more susceptible to disease than those propagated by grafting.
It's unusual that your pip has already sprouted. Normally apples need a spell of cold conditions to make them germinate. Maybe it was in cold storage for a long time before it got to the shop. Just plant it in ordinary potting compost, and see what you get!
To germinate pips that haven't sprouted already, remove them from the apple, wrap them in some damp cloth, seal them in a plastic bag and put them in the fridge (but not in the freezer!). Check every 2 weeks that the cloth is still damp and see if any of the pips have sprouted. If they have, plant them in a pot.
If you have no success after about 10 weeks in the fridge, give up - apples have a poor germination rate, and one in four germinating is better than average.
(Of course the "easier" way is just to plant them in the ground out of doors, and let winter do the chilling for you)
To be honest you would probably do better buying a tree that is grafted onto a dwarf or miniature rootstock. They are perfectly hardy grown outdoors (even in Scotland) - they will need a 24 inch pot or container when they are mature. If you try to grow one indoors, it will probably not get enough light. All fruit trees really need full sun all day.
Also keep in mind that apple trees are deciduous - they drop their leaves in autumn so your "house plant" will just be bare branches for 5 or 6 months of the year. If it doesn't get cold enough in winter when grown indoors to make it drop its leaves, it won't thrive in the long term.
I've grown several Apple saplings from sprouting seeds, and I've just put them into seed raising mix until large enough to be potted. However, one I grew out in water or in my Aquaponics system and that's about 6 years old now.
This 4 year old one is in a air pot since I didn't want the tap root killing the tree.
But since it's over 7 foot tall I suspect the roots have grown across the air gap into the ground.
Neither have flowered yet and I don't recall which Apple I got them from since it hardly matters since any fruit I get won't resemble its parent. I assumed the seeds had cold stratified in long term refrigeration storage.