Question
I live in San Diego.  I have a friend who has a large flowering orchid
plant in a pot outside on her patio.  I'm not sure what kind of
orchid it is, but the flowers are large and purple.  What would be
the best way that I could take part of this large plant and transplant
it in my yard?  Can you transplant a stem? or do you need to get
part of the root with the stem? i. e. should I break the plant apart
and take a stem that has a root attached, etc?

Answer
The general rule of thumb in dividing an orchid plant is to remove a minimum of three growths with the intact roots to pot up as a new plant.  They like to be firmly anchored in their new pot to facilitate growth.  Also, be sure to pot the plant in orchid potting mix which can be obtained as small hobby bags at garden centers or mass marketers such as Lowes or Home Depot.

Healthy roots are critical to survival and growth and orchid roots need a mix that provide for good drainage.  I would try to reproduce your friend's growing conditions with your division as far as sunlight, temperature, watering, feeding, etc..  There is nothing that succeeds like success.