I am going to be the riches farmer ever! Lol 

what does special mean?

It means the casting time depends on different situations. In this case, it is special because the spell can either be cast using one action and have one effect, or be cast over 8 hours and have a different effect.

Anyone have advice for me? I intend to use this as the Action to control the battlefield. It says I can exclude one ore more areas of any size within the area. We are fighting large and huge creatures, could I make 5 foot wide long pathways through the over growth, offering free full movement for my medium sized team mates while still costing the larger creatures extra movement on their turn? Being able to slow down Hill Giants and Ogres to a crawl while our team abuses them with ranged weapons seems super helpful. Our Crossbow fighter has been waiting for an excuse to use his new magic crossbow and bolts.

Quote from BadhandsBob >>

Anyone have advice for me? I intend to use this as the Action to control the battlefield. It says I can exclude one ore more areas of any size within the area. We are fighting large and huge creatures, could I make 5 foot wide long pathways through the over growth, offering free full movement for my medium sized team mates while still costing the larger creatures extra movement on their turn? Being able to slow down Hill Giants and Ogres to a crawl while our team abuses them with ranged weapons seems super helpful. Our Crossbow fighter has been waiting for an excuse to use his new magic crossbow and bolts.

I would personally say yes, but it all depends on what your DM thinks. So I'd ask them to give an answer to your question.

Just imagine how happy Edermath would be if you used this on his orchard :)

I would allow it,  but I would also hinder your plan dramatically as if you have that much overgrowth thats stopping Giants then there is going to be concealment from ranged attacks due to that same thickness of the plant growth

A big note about this spell is that it has no duration - it doesn't last for a minute or an hour. Its indefinite. Further, there is no save involved. 

RAW A 100ft radius can extend that far upward, potentially messing with flying creatures. 4 feet of movement for every one foot moved means that moving on a grid square, 5ft costs 20ft of movement. That'll slow anyone down 

I wish there was a guide on what this did at higher levels. It should be more powerful at higher levels. for example, it could add 1/3 the distance for each lvl higher than the 3rd level it's cast.

it means there is two potential options for the time and not something that is set in stone. one is instantaneous when cast and the other takes 8 hours to cast

So... If someone has a garden with some shrubberies that potentially could grow high, like the ones used for high hedges... You can use the one action version to make these overgrown, right? Since the plants can go high, and 100' radius can also mean up, and you can exclude areas at will...

That does mean that you can make instant and permanent-until-cut-down offensive to the owner statues in said garden, right?

I'm planning to take this spell for my bard pirate, and I want to have some nonlethal actions at hand to make my distaste for certain people known.

Or you could make an instant labyrinth 😁 Cool party trick. 

If long casting it doubles the yield of food crops over a large area, I wonder if the 1 action version has any effect on food crops? Like would it rapidly grow vegetables to be ready to harvest in seconds rather than months, or would it just make a vegetable bed overgrown and weedy?

Could I make the area with another spell in adition difficult terrain so anybody have to use 8 feet for every one feet he moves??

The secondary effect is amazing for world building.  It gives us a really concrete benefit to having a druid circle or nature temple in a settlement.

is there an opposite of this spell? like destroy land or something

Yeah, it’s called Fireball :P

yeah I mean there's that..... not sure what I was expecting

Combine it with Spike Growth to create a basically impassible bottleneck in the area where they overlap. You get an area of rough terrain (1/2 movement speed) plus an area of 4feet of movement cost per 1ft moved (NOT 'rough terrain' so it does stack). 

This means that it will cost 40ft of movement to go 5ft, (half movement, with each foot costing 4 feet. So your 40ft of movement goes down to 20ft for rough terrain, and then down to 5 feet of movement per turn in the Spike Growth area, or 1/8th movement.)  which pretty close to immobilizes anything with a movement speed of 40 or less.

I'm not entirely sure that's true. Why, then, are there spells that have a cylinder or sphere shape? Would this mean that "radius" spells are domes?

Then cast spike growth on top of that...