Dawn of War Codex

I'm wondering if there are strategies I'm missing for dealing with garrisons as Tyranid. I know it's something that bugs tend to struggle with.

How I normally deal with it is to have 1 spore mine in my opening build on maps that I know have garrisons around points I need to contest. The problem is maps with multiple garrisons around points that need to be contested (for example, Green Tooth Gorge). It doesn't seem cost efficient to have multiple spore mines, but against certain builds I don't necessarily want Warrior barbed strangler. Is the only option then to move somewhere else on the map and try to force my opponent to respond and then get Zoans in T2?

It seems that nid heroes don't really have anything that can really deal with garrisoned units, I thought maybe the HT's bio plasma but it doesn't seem to do much.

Is there another course of action I'm missing?

What you are generally saying is correct.
strangler wariors, spore mines, or ignore and go to the rest of the map. T2 zoans clear them out.
You could use the RA mines on entrances. Due to how the game works it'll do massive damage as the model are all bunched up when they get out.

You can completely blow up a garrison building (2500hp?)with a single spore mine squad I think. It may be worth it to even preemptively demolish a particularly troublesome garrison that your opponents TM, warpspider etc can repeatedly abuse throughout the match. For example, the one overlooking the natural VP on GTG.

wut? A single spore mine squad will never do that much damage to a structure. Only towers from tyrannoformation can one shot structures whatever their hp are.

Spore mines do no function like grenades vs garrisons since they do not have that weapon type which determines how a weapon damage reacts to buildings. Spore mines only hit the models that are in the windows as the other models are technically "not there" making spore mines actually piss poor at dealing with garrisions and completely unreliable.

But try to not engage them at all until zons. Not much you can do. Stangulars are a meh choice as well because you cannot reach the garrison if its well supported by range fire of suppression. But they are more reliable than spore mines not to mention their utility.

We can see who hasn't been keeping up with Torpidmines.