You might not realize it, but watching Zach Galifianakis poke around in the dirt like he’s just discovered it is exactly what you need right now. In “This Is a Gardening Show,” a six-part series premiering April 22 on Netflix for Earth Day , the actor and comedian brings a kind of wide-eyed curiosity to gardening that feels at once sincere and ridiculous. The episodes run an easily digestible 15 to 20 minutes each — just long enough to learn something new without feeling overwhelmed. Learning