They probably can't survive the average Colorado winter. Could be a place in the southeast or southwest portion of the state but chances are low.

Did you ever get some seeds? I usually have more then I need (although not this year 2008). I have perhaps the largest living Joshua tree in the Victorville area. It is easily 40 ft tall. I am a desert landscape designer and have used Yucca brevifolia many times. When young the plants can be transplanted with little regard to original orientation. As the "trees" get larger transplantation becomes more problematic. Larger plants dug out of the ground usually will not survive due to extensive root damage. Small container grown plants or volunteers can be planted into almost any well drained location with full sun. It doesn't matter how they were facing. Their growth rate is dependent on water. The more water they get the faster they will grow. They will not tolerate water logged and clay type soils. Sandy soils are preferred as well as overhead watering. Seeds germinate better if soaked in water or scarified. I have read of people having specimen plants in England and the Eastern US. I sent some seeds to a gentleman in France last year. Their native range includes not only the Ca Mojave Desert, but parts of AZ, NV and UT.

I have a Halesia Carolina in my yard, and every year in late Spring I am drawn to the area where it's planted by an incredible scent. The flowers remain on the tree only for about a week and a half, so I can't be sure if it's the Halesia, or the wild honeysuckle. I can't find a reference on the net that says that the Halesia is a fragrant plant, but it's a real magnet for me in the spring. If you look around your area for the seed pods/drupes, and find them, we may have solved a mutual mystery. Please keep me informed. Thanks.

I have been reading through the interesting posts on the Joshua tree, especially from the original post of kazooie(kapiti coast, NZ}. I think someone forgot to ask how much rainfall that they get on the New Zealand coast. That would be the first thing whether or not you could even grow it there. It is a true desert plant and survives on very little rainfall/snowfall in one of the driest deserts in the world. No drip systems or anything is needed, but it has to be a climate that is very comparable to the Mojave. We grow them successfully here in southwest Idaho, but we are an extension of the Great Basin Desert, and only at 2,600 feet. We range in rainfall here in our valley from 3 inches to 10 inches in good years, which is not very often. And they can take extremely sun, but humidity is another factor that could be lethal to the plant. These true desert yuccas tend not to survive in semi to tropical countries unless there is a greenhouse situation. Also, it must have a definite winter resting period, or the plant will not survive long. Doesn't like much of the winters in Phoenix, Palm Springs and such. It never quits growing. There are related species from Mexico that do much better and thrive without that winter cold.