word - One at a Time Riddle

This riddle borrows a format from Guess me riddle #4 by Quark-epoch.

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The word is a four letter word which is in the oxford dictionary

My first letter is a green cut-out vital sign.

My second is however, a shelled kernel.

My third is, out loud, top of the game.

My fourth is a dame’s healed tree organ.

My whole is what you simply read.

Now answer me this, what am I?

Note + Hint:

This might require a little botanical knowledge.

Answer

I'll try for:

Post

My first letter is a green cut-out vital sign.

@rhsquared has suggested P

My second is however, a shelled kernel.

Perhaps an OS, or operating system. Thus O
Per @jafe however is synonymous with though, and shelled kernel is also a nut, thus though + nut, or doughnut (phonetically similar), or O (based on shape of doughnut)

My third is, out loud, top of the game.

Shrug*. Dunno if I'm supposed to get the letter by saying "top of the game" out loud (and identifying something sounding the same), or if it's related to a sport like baseball etc.
Again, per @jafe the top card in many games is the ace, which sounds like "s"

My fourth is a dame’s healed tree organ.

My best guess here is tea which is phonetically similar to the letter T. Healed tree organ make me think of cured plant parts such as leaves, which are used to make tea. Or possibly, by dame's you're referring to flowers which have petals which when dried/treated/cured can also be used in tea.

My whole is what you simply read.

We read posts here on this site.

Special thanks to:

@rhsquared and especially to @jafe. Would also like to find a way to share with them :)

Edit: Apologies for the delay, update is finally here.