Wilderness
'Wilderness' signifies something with little life in it, as described in the internal sense in Luke 1:80 'Wilderness' signifies somewhere there is no good because there is no truth. 'Wilderness,' as in Jeremiah 23:10, signifies the Word when it is adulterated.
(References: Arcana Coelestia 1927)
Garden
Plants, in general, represent knowledge, ideas, and intellectual concepts -- things of the mind. Plant the best and most beautiful of those in one place, give them plenty of water (truth from the Lord about day-to-day things), plenty of sunlight (the Lord's wisdom) and warmth (the Lord's love), tend them to keep the weeds (false ideas) out, and you get a garden. So it makes sense that a garden in the Bible represents the intellect, where with proper care we can nurture the best and most useful ideas and ways of thinking.
(References: Arcana Coelestia 98, 100, 1588; Heaven and Hell 111)