Even if I knew that tomorrow the world would go to pieces, I would still plant my apple tree. -Martin Luther
I've never seen a context for this quote, nor an accurate reference. So please, don't use this quote! It's probably not from Luther.
check this one out:
One morning, old Dr. Martin Luther leaned out his kitchen window. The sky was blue. The yard was full of chickens. The dog was asleep on the porch. The apple trees in the orchard looked like wedding dresses, white blossoms shining in the light. Dr. Luther drew a breath of April air. “Even if I knew the world was going to end tomorrow,” he said, “I would still plant an apple tree today.”
This seems to be a total fabrication. This webpage debunking Ellen G. White claims:
Yet another example of running down a quotation comes from the Luther.de site that says:
Many more legends about Luther and trees swirl around, one of the best known should be mentioned, the famous saying: ‘If I knew that tomorrow was the end of the world, I would plant an apple tree today!’ is attributed to Luther. One must remember, that the first written evidence of this saying comes from 1944...The 1944 date may come from Martin Schloemann’s book which has a section on the apple-tree quote.
I, Yoel Natan, think the Luther apple seedling quotation was invented and attributed to Luther in 1944 or before, but it comes by way of an ancient rabbi, Rabban Yochanan ben Zakkai, who survived the sacking of Jerusalem in 70AD. Claudia J. Setzer wrote:
While they [rabbis] retained the idea of longing for a messiah, they did not encourage chasing after one. A Tannaitic source reads, “He [Rabban Yochanan ben Zakkai] used to say: ‘If there were a plant in your hand and they should say to you, ‘Look, the Messiah is here!’ Go and plant your plant, and after that go forth to receive him’ (‘Abot R. Nat. B 31).
I haven't sifted through this stuff, so I can't vouch for it being legitimate. However, that the quote has no documentation anywhere should raise a red flag.