Crowds in April, rain in June - when to go?

We're planning a trip to Japan next year, and are bending towards either going in April (flowers and crowds) or in June (rains and greenery). A big part of what we want to do involves going to parks and gardens, so we'd like to know:

how bad are the crowds in April, really? Just "you won't easily get a seat," or Disneyworld lines and looking at a temple as if you were in a rush-hour subway car? We would spend the last week in Tokyo, so I guess Golden Week wouldn't be so bad?

and

how rainy is June, and what kind of rain? Is it that we'll see Korakuen through a drizzle or that we won't be able to step outside the house? And are there any late flowering trees in June?

Thank you all very much.

I would avoid June at any cost! The rainy season is terrible here, it is not just a small drip here and there, it is a shower.

I'd rather want to see one garden in April during cherry blossom than 100 during June in rain.

Go in May, the weather is awesome, and if you want to see cherry blossoms, just head north at the beggining of your trip :)

On which dates in April / June 2015 can you travel in Japan?
Will you travel only in and around Tokyo?

Both cheery blossom season and rainy season depend on years and areas. And now it is too early to estimate when the seasons will be in 2015 in a particular area.

Golden Week 2015 holiday season will start from around 25 April.

I'm weird, but I love the rainy season here in Japan. The hydrangea are gorgeous, the temperature is nice even if its rainy, and while sometimes you'll get heavy rain, often enough it's just a drizzle and perfectly manageable with gear. Also if you're here in early June, it often doesn't start until mid-June anyway, depending on the year, so it might be fine.

For first time visitors though, April is probably better!

Or if you want a black-hole period, try in January, just after series of Holidays at the beginning of the year. Cold in January though.

In rainy season, always I think I'm in the hell of humidity. Not rain but humidity!
But yes, as scarreddragon suggested, hydrangea are so beautiful, I love to watch them in Kamakura or by the street in Tokyo.
hydrangea: http://goo.gl/LuOfsX
In cherry blossom season, I'm afraid to say the flowers soon finish scattering, so you can watch them in an unpredictable short time.
So if you have long time to stay, April is the best, but if not, I can recommend June also.

I've been to Japan in late June and it was great. We were there for 8 days and only had two days of really heavy rain, the rest was overcast to sunny and always warm. Few people, Miyajima for example was nearly deserted.

I liked it. :)

I also spent some time in Japan from late March - early April. Great weather and cherry blossoms but lots more tourists.

It depends on how you tolerate the heat. Mid to late June can get hellishly hot especially in Kyoto which is in a valley so it seems to get the extreme heat, though there arent many tourists around so it is pretty good to travel into the mountain areas. Hakone is pretty good that time of year and so is Takayama, and I'd expect Kanazawa and Karuizawa but that woiuld be peak time there. May is really nice. Mid to late May would be my pick - well after golden week. I didnt like travel in cherry blossom time. It was riddled with tourists. The cherry blossoms were nice and you get to see a different side to the japanese (because they let their hair down), but it had its challenges. Late March was pretty good, though - just when the blossoms were coming on. And there was still snow about in some places.

Maybe go in April, but before Golden Week?

My experience is that you can have good weather without the crowds. You *might* not be in prime cherry blossom season, but that depends on the weather in any particular year and also depends on where in Japan you plan to visit.

Hey all

Thanks for the answers. May is, unfortunately, not really an option. I don't have much of a problem with humidity (being originally from Rio, which is both tropical and by the sea), but it's more of a problem for my girlfriend; the real deal breaker would be monsoony rains where you couldn't get out of doors.

As for the crowds, we aren't necessarily looking for a black hole period, just afraid of overly dense crowds - long lines at tourist attractions, difficulty viewing stuff, need to book well ahead (we're going to use a JR Pass and wander a bit).

Is Tokyo also hectic during Golden Week, or have most people gone to the country?

What about late Juli or Beginning of August?
Of course, it's hot and still humid, but it only rains for 5-30 minutes per day. Totally manageable and coming from Brasil you might find the weather not too hot.
(I'm from "cold" Europe and it was still ok for traveling :) )

Tourist spots weren't too crowded, although I wasn't in Disneyland.

Maybe just as an additional option?