Cactus growing into blocks

What I expected to happen was for the cactus to
Grow until it reached the blocks above it
I though it would grow into the blocks above
Even though there was no space for it to

The cactus grew into a opening , but there was
No space for it to grow in that area because the blocks beside
It was covered

1. ...Place a sand block, Then place a cactus atop
Of the sand block
2. ...Leave two spaces above the cactus for it to grow
3. .. On the third space put blocks around it and wait until
It grows