T he Scotts Miracle-Gro Co. offshoot that targets young, urban gardeners has acquired a Santa Rosa, California-based hydroponics company popular with marijuana growers. Hawthorne Gardening Co., a Scotts subsidiary formed in October, purchased General Hydroponics Inc. and Bio-Organic Solutions Inc. Terms were not disclosed, but the acquisition should position the company in the growing marijuana market. Subscribe to Upstart Today for a daily jolt of startup news and powerful ideas. Jim Hagedorn,…