I wouldn't know really, but I would expect that you would put t down when the grass is growing, just like fertilizer, weed killer, etc.
If then God so clothe the grass, wich is today in the field, and tomorrow is cast into the oven; how much more [will he clothe] you, O ye of little faith? (Luke 12:28)
For if we live, we live to the Lord, and if we die, we die to the Lord. So then, whether we live or whether we die, we are the Lord's. (Romans 14:8)