Birchnut trees grow the same as every other tree: Sapling, small, medium, fully grown.
The life cycle will then reset back to a small tree after that.
Unlike other trees, birchnut trees will not drop any birchnuts when chopped before it isn't fully grown.
It will also only drop 1 during Summer and Spring, but won't drop any during Winter.
Birchnut trees will start to lose leaves a few days before winter, so it's recommended that you only chop down trees with leaves as they will still drop birchnuts.
Autumn is the best time to be chopping birchnut trees as they will drop 2 birchnuts, leaving you 1 to keep and 1 to replant.

Cutting down a fully grown birchnut tree that drops birchnuts from day 3 and after, there is a small chance that nearby fully grown birchnut trees will turn into poison birchnut trees.

The chance will increase with the amount of days survived, starting from 3% on day 3 to 33% on day 70.
After enough time, poison birchnut trees will revert back to a normal birchnut tree.
As with lumpy and evergreen treeguards, you can plant birchnuts nearby to attempt to pacify it.
The poison birchnut tree will not move like other tree guards, however.
Instead it will stay in the same spot and spawn up to 5 birchnutters to attack and also send homing tentacles that will attempt to hurt the player.
The poison birchnut tree doesn't take normal damage and will instead take 18 axe swings to die.
A poison birchnut tree will drop 3 birchnuts, 1 living log, 20% chance for a nightmare fuel or an extra living log.
The stump can also be dug up to yield an extra living log.
Since the poison birchnut tree takes 12 chops instead of normal damage, Woodie can easily use Lucy The Axe to kill a poison birchnut tree.
You can also burn the poison birchnut tree, which is the easiest option including murder. Just try not to start a forest fire.
You will not get any items if the poison birchnut tree gets burnt.
Poison Birchnut trees cannot spawn before day 3.
A poison birchnut tree can take 18 axe and luxury axe swings, 9 Lucy the Axe swings and 8 moon glass axe swings before death.

Now lets get to the main part, how birchnuts can be used for food.
Birchnuts cannot be eaten until cooked over a fire.
While raw, birchnuts will last 20 days before rotting and will only last 6 days while cooked.
Putting a raw birchnut inside an ice box will make it last 40 days, making it great for stockpiling.
Cooked birchnuts can be eaten for 9.375 hunger and 1 HP, meaning that a fully grown tree will give you 18.75 hunger and 2 HP if you eat both birchnuts.
Just remember that most players like to take birchnut trees for food, so remember to replant once and a while.
As for the crockpot, cooked birchnuts can be used as filler.
Unlike other filler, birchnuts can only be placed inside a crockpot when it is cooked.
Cooked birchnuts can also be used to make trail mix, which can be made with 2 berries, 1 twig and 1 cooked birchnut inside a crockpot.
Trail mix will give 30 HP, 12.5 Hunger and 5 sanity. Trail mix is one of the main uses for birchnuts as it is a great early HP source.
Since birchnuts only give 1 in most seasons, it's best you save them for the crockpot. But they are a nice source of food early on.
As with every filler, cooked birchnuts can't be used in everything. So be careful while cooking.

That's about it for birchnuts.
If you'd like to me to add anything, please say so in the comments.

I hope this guide taught you something about birchnuts, an overlooked tree type.

I do plan on making some more guides, if you have any suggestions please leave those in the comments as well!

Have a good day and thank you for reading my guide!