A technique that seems useful, but might not be, and probably isn't

Oak saplings won't grow into giant oaks when planted on the 8th block from the bottom. However! If you place 3 blocks next to the sapling as shown in the image, they will almost certainly grow into giant oaks. Bone meal is required, but it might be worth trying if you don't have wood early in the game. Well, I used this a lot intentionally because I wanted to grow a ton of giant oaks on my map.