I am not sure how well known these trees are, however Joshua Trees exist wildly in the dry area in the south part of California, including Joshua Tree National Park, which is a few hours away from Los Angeles by car. Joshua trees are a kind of succulents, and large ones grow to 30 feet. Seeds are available at the visitor center in Joshua Tree National Park, but they are not available in general nurseries.
How to Grow a Joshua Tree – Seeding
The seeds require 15C/60F or warmer temperature for germination. So, it is recommended to seed them between the spring to the autumn, when it is warm. Cover the seeds with 1/8 to 1/4 inches of soil. It takes 11 to 21 days to germinate. Seed them in a container with holes at the bottom, and place it in a bowl or a saucer filled with water to keep them moist, until they germinate.
How to Grow a Joshua Tree – Location
Because they like sunlight, it is recommended to keep them near the sunny window or on the balcony. Young plants like warm temperature at 25C/87F or higher.
How to Grow a Joshua Tree – Watering
Though high moisture is required until they germinate, they prefer to be dry after the germination.
How to Grow a Joshua Tree – Transplant
They can be transplanted when they are as high as 1 and 1/4 inches.