In regards to your question of when the last gardening bonus was ... it occurred January 10, 2018. Going by last year's bonuses we should have had one in April. When the next will occur...who knows. I do hope it will be soon, though.
As stated previously, we had a double gardening event on 10 January - 14 January this year.
Last year, there were double gardening events in March, June, and Aug/Sep for the birthday event. Going by that, it seems they happen every 3-4 months and therefore, we are due for another one soon.
I was thinking it usually happened around Valentine's Day or March; las year, it was 1/18 thru 1/22/2017, 3/8 thru 3/12/2017, 6/6 thru 6/11/2017.
Hope it's soon too; way overdue. I really appreciated the free fishing . . . should be free all the time, Fishing, crafting, gardening and pet training is way too much for the small amount of energy we get and they need to have a different energy for each of them.
Alia Misthaven