Today is when I will call for contributions.
But, there is some leeway.

What is happening now?

I'm receiving contributions, and will continue gathering late entries until May 25*.
I am organizing an online Spring Report.
I myself will be getting caught up...

* This should roughly correspond to when the warm spring rains have raised the soil temperature to 64 degrees, and the cicadas have emerged in full force.

How strict is the theme?

I've laid down ideas in the first introduction, but with collective projects that I organize I tend to treat my own ideas as catalysts and personal artifacts, and then wait and see how people want to address them, or what elliptical orbit they may prefer.

Do the contributions need to be well-organized?

Not at all.

I just received a .zip from will sōderberg and Marie Waltz, and it is a grab bag of garden photos, adjusted garden photos, materials about a nun who penned a devil's letter in 1676 and the efforts to decipher it, Ogham Stone images, and an entire 1846 dictionary of gardening.

After May 25?

Now that my teaching term is almost out of the way, and once I've finished my own artwork and the online collection, I'll spend my time thinking how this can feed into a physical summer event.