Culling the dragonfruit Seedlings: This step in growing dragonfruit from seed is vital. Up until this time the amount of time and energy spent on your part for growing any of the dragonfruit seedlings individually is next to nothing. Starting the dragon fruit seeds was quick and easy, but from this point on you will be devoting substantial time and work to each individual dragonfruit seedling and the dragonfruit cactus plant it will mature into eventually. Now is the time to eliminate any weaklings and to keep your standards high for the seedlings you keep vs. throw away.
Be Cruel! Any dragon fruit cactus seedling that isn't a top specimen should go! It doesn't matter if the reason was that the dragonfruit seed was not good to start. If the corner of the tray became too dry, or it it became too wet and some dragonfruit seedlings didn't grow well. Whatever the reason, if any of the dragonfruit seedlings are not robust and healthy, discard them! Even if the entire tray of dragonfruit seedlings isn't up to par, it is better to start a new tray than to push the failed tray to become a success. You want to start your dragonfruit cactus plants only from the best stock. Likely most all of your seedlings will be of excellent quality, but always be ruthless.