Yes, with limitations, and only inside a private residence. The County prohibits outdoor cultivation of cannabis.
For medicinal use, each qualified patient with a medical marijuana identification card may cultivate up to 12 plants inside his or her private residence.  Cultivation for medicinal use is limited to no more than a total of 24 plants per private residence, when more than one person with an identification card or primary caregiver lives at the residence.
For recreational use, a person over the age of 21 years old may cultivate up to six plants inside his or her primary residence. And, no more than a total of six plants per private residence may be cultivated for recreational use.
Under no circumstances may more than 30 plants – 24 for medicinal use and six for recreational use – be grown in any single private residence.
All indoor cultivation must comply with the County Code, which requires that any cultivation occur within a fully enclosed structure, with solid walls, and a ceiling, roof or top.  The cultivation must be conducted in a designated cultivation area separately secured and locked from all other uses in the residence.  Plants must be reasonably secured from theft and from access by minors or other unauthorized persons. Cannabis must not be perceptible from the exterior of the private residence. If the residence is not occupied by its owner, written permission from the owner or landlord is required.  Anyone interested in growing cannabis within the unincorporated areas of the county are advised to review the cultivation requirements in Chapter 84.34 to Division 4 of Title 8 of the San Bernardino County Code, which is available for viewing on the County website.