I am new to gardening and also not familiar with lawn care in Tropical climate. We've got lots of crabgrass this summer. I used Weed B Gone for spot-treatment and most of them seem to be dead. I do not even know if they ever die down until the next season, or do they keep going all through the year?!

Here's my qestion,

When is the best time to put down the crabgrass preventer here in Hawaii?

Thank you for your time and any input will be greatly appreciated!