Out of all the things that can be interpreted in this poem, the title is probably the most straightforward seeming one, but it can also hide a plethora of hidden meanings. It could mean the poet wants to be outside with nature, maybe grow some lemongrass, or they just want to touch grass.
The word count is significant, because the less words, the more symbolism and meaning is packed in them. In this case, it showcases the immense amount of longing the poet has for grass.
Like in the title, the word grass can refer to multiple things. The outside, lemongrass, theoretically some trees, or just your garden variety of grass. However, the difference in meaning between the title and the poem is that the title is more interested in the action, that being the longing, and the fact that the poem itself is 1 word, which is much more "meaning dense".
With all that being said, the picture becomes quite clear. The poem is about an unknown person that has a deep longing for anything grassy. They desperately wish to go outside, and touch the nearest field of grass they can find.