so i just heard about solarpunk today and i LOVE the idea. 

Does the vertical garden in Milan count as something you could call “solarpunk”?

Yes and no
The buildings themselves ‘yes’, the context they are placed in ‘no’

Vertical gardening in cities is a great way to add foliage in a place where horizontal space comes at a premium! They clean the air, and make an otherwise depressing modern architecture style nicer to look at~

However, context matters possibly more than the building itself. 
The “towers in the park” method of building was tried extensively, especially in New York, post-WWII and failed miserably
Developers thought they were doing something nice by building low-income housing smack-dab in the middle of a lot of “green space”
But it ended up being the opposite of a nice thing in practice, by and large because of all that open space, there was nothing within practical walking distance. No shops, no jobs, no entertainment, no clinics. You force people to need a car to get around for practical purposes, and if your building is for low income residents who can’t afford a car, you get a lot of isolated people with nothing to do but stare at grass. That’s why “the projects” as those towers in the park were called ended up slums. It wasn’t a nice place to exist, and people didn’t like living there, and it was an all around depressing experience – even with all that green space many city planners love so much (really because of all that green space, which made everything far apart from everything else).

For a city to really be “green” in the environmental impact sense, you need to design it in such a way that people can make low-impact choices without thinking about it, or trying to do it really.
Maybe the single biggest thing we can do is make mixed-use buildings legal to build again – “mixed-use” means more than one use is allowed in one building, “uses” are things like  “residential”  “commercial”  “civic”  “office”  “industrial”  and so on. In most places in America, zoning is separated by use, de facto making mixed-use illegal (except by special exception, which is hard to get by small local developers). But what happens when you build single-use buildings in neat little zones? You get a whole population of people who need a car to get from place to place.
But when you build like cities used to be built, with apartments on top of shops and so on, the daily things people need to do are closer to where they live.. so it becomes practical for more people to walk, bike, wheelchair, or transit to their destination… or still drive if they really want or need to for other reasons. 

Really, driving less or not at all is what we can do to collectively lessen our impact on the environment – this would have more impact than building “green housing” – and building mixed-use communities where most things people need are withing 5-10 minutes walking/wheelchairing distance is how we can do that. Basically making walking or rolling on a bike or wheelchair just as practical, or more so, than getting around by car (not by making driving a car any less practical, but by making those other modes much more practical than they are now in America).

So yeah, on top of all that, vertical gardens on our buildings would be a cool plus! But vertical garden apartments put in the middle of a park with no jobs or shopping directly nearby makes drivers out of all the residents, and that would counteract any environmental savings made by the building itself. 

So yeah, those building would be much “greener” if they were mixed-use (can’t really tell from this picture) and if they were closer together so things people need are within practical short walking/rolling distance. 

191811110: “USA has buildings legally stuck on one use only Oo? So there’s none of the groundfloor of any bunch of blocks flocked together – progressively becoming shops, kindergartens, hairdressers and so on? That’s sad :(.”

It’s not quite that simple. New York, for instance, has what you described. But yeah, our zoning laws have become messed up and we need to do something about that.