You might try limiting your search to the forum most likely to have the information you're looking for. To use your example of fig trees, try searching in the Vegetables and Fruit forum. And for the individual threads, you can change the number of items per page that appear on your screen to a large number (you do that on your Profile page under "site preferences"), then use the search page function (Control F, in case you aren't familiar with that) to locate a key word.
There may be a better way, but that's what I'd do.