Grass, Weed
You plant your flowers in the light of the sun in the shape of a cross, but it's too hot—the sun is too strong—and you end up with grass. Flowers can't grow in these conditions.
Think of how disappointed you are. You wanted a beautiful cross of flowers, and now you just have a big overgrown patch of thick grass. It isn't even pretty green grass, it's a little brown and damaged from the sun.
そう
くさ
None
The grass on top is brown and burned from the sun, so you need to take a cool saw (くさ) and hack the tops off. The saw is actually physically cool to the touch, to help heal the grass' sunburned bits. It just happens to look cool too.
Imagine using your cool saw to saw off the heads of all of this grass. You made the cross pretty big, so there is a ton of grass to get through. The sun is beating down on you and the grass too, which isn't making it any easier.