A few things that I'm interested to know about:
- What's the required temperature for growing walnut trees (Juglans regia)?
- Do they grow in hill areas?
- How long does it take to produce fruit from the day it was planted as a young tree?
Minimum temperature changes among walnut (Juglans regia) varieties (where I live, the walnuts withstand -30 to -40°C / or -22 to -40°F). The maximum temperature is generally around 35°C (95°F) and above this the twigs, leaves and fruits start to burn. Walnuts survive even if the temperature goes occasionally in some days to 45°C (113°F), although I don't know for how long.
They grow on plain and hill areas and they require a lot of sunlight, so if you plant them on a slope, choose the sunniest side, usually facing south, SE or SW. If the temperature rises above 35°C (95°F) on a regular basis, then plant the walnuts on the NE or NW side of the hill.
If they are planted from seed, they will fruit after 7-10 years. If they are planted from commercial varieties (usually grafted, but not always), they can start bearing fruits 5-7 years after purchasing, assuming they are at least 2 years old. In any case, a consistent harvest will come after 10 years.
There are also a few things that need to be taken in consideration. First, walnuts don't like overwatering, and second they don't like growing in shaded areas. So, if you plant a walnut tree in a rainforest, it might survive, but it won't thrive. To improve their chances, plant them at a safe distance so other trees don't cast shadows on them, and make sure the water is draining really well.