To the extent that weed is legal today, it is highly regulated and the rules vary quite a bit from one locale to the next, and state to state. Your best bet is to do a lot of research, armed with the following general principles, and then talk to a local lawyer.
If you are growing weed legally and want to sell to dispensaries, you'll need to ensure that you are licensed to do so. Marijuana is an agricultural product and one that is very new to the legal market. As such, there are many restrictions on how much you can grow, how your crop is laid out in a plot, pesticide use, and placement.
Remember too that in many places where marijuana is legally sold, it is for medical purposes. That means your weed must be of a particular grade and quality, following certain processes. In addition to ensuring that your crop follows all requirements, you must inquire into local ordinances about selling to dispensaries.
Working With Dispensaries
Given the variation in state laws, and the fact that individual localities have their own rules, you will have much to learn before you deal with your customers' needs. Dispensaries will work with legal growers, generally speaking, but just like any type of business, each will have its own requirements.
Some may only sell organically grown products, or work with cultivators who follow a particular process. Apart from this, there will be quality and price concerns, as well as questions about your capacity to supply reliably and regularly.
Growing professionally is not like having a few pot plants on your back porch. The canna-biz is a booming new area of cultivation and profit and the smart money probably is on getting in early. But entering any industry is difficult and this one is particularly iffy.
Talk to a Lawyer
For anyone seriously considering cultivating marijuana professionally and selling to dispensaries, a talk with a local lawyer is a must. Many attorneys are as interested as you are in this area of law. You can find someone to guide you so that you avoid trouble. Grow your weed legally and properly licensed.
If you have been charged with a crime associated with your possession or cultivation of weed -- or anything else -- talk to a criminal defense attorney. Many lawyers consult for free or a minimal fee and will be happy to discuss your case.