Grass blocks in pokemon heart gold are were wild pokemon hide you may catch them and train them or you may beat them with your pokemon and earn exp.
you can't...
blocks are exclusive from pokemon diamond,pearl and platinum,so you can't get it. But you can feed pokemon with beries.
You can get one in Viridian Forest.
yes ice is super-effective against grass
in safari zone area:meadow in grass
You capture Zirachi in MT Silver on the grass
grass
The Johto starters, Tododile the Water Pokemon, Chikorita the Grass Pokemon, and Cyndaquil the Fire Pokemon
dunno about heartgold, but in soulsilver it is in that area of grass under the day care and you have to headbutt to get him too.
The starters of HeartGold will be the same as Pokemon Gold and Silver which were Chikorita (Grass), Cyndaquil (Fire) and Totodile (Water).
since you have the national pokedex,go to grass to look for pokemon.or you can migrate.
you get it in the powerplant in Pokemon firered/leafgreen but in soulsilver/heartgold you get it in the grass out side of the powerplant