Starting Wednesday, there's nothing to keep Oregonians from adding a cannabis plant or two - or even four - to their backyard vegetable gardens.

A couple of caveats: You've got to be 21 or older to possess and grow cannabis in Oregon and your yard should be a private place where neighbors and passersby can't easily see your plants.

Oregon's new marijuana law allows people not only to possess marijuana, but also to grow it at home. Every household may have up to four marijuana plants.

While growing is legal starting this week, buying plants is not. Only medical marijuana patients and caregivers can purchase starter plants from dispensaries. For now, people who want to grow backyard pot will have to rely on the generosity of friends who grow.

Neil Bernstein's advice: Ask nicely.

"To be more than two people removed from a marijuana grower in this city is hard," said Bernstein, owner of Roots Garden Supply, a North Portland grow shop that serves cannabis growers.

Once you've got your plant, what do you do?

Don't be intimidated. "It's harder than a tomato plant, but not difficult to grow," said Bernstein, who plans to host a weekly series at his shop on how to grow at home. "The difficult part is harvesting flowers that aren't going to have mold and mildew."

Mold and mildew, as any skilled grower will tell you, can ruin your crop.

Inside vs. outside? Start outside. The initial investment is cheaper compared to an indoor set up and it will give growers a season to get familiar with the plant, said Bernstein.

"It will be the lowest cost way to experience the plant's life cycle for the first time," he said. "No one starts out as an expert grower. Like anything in life, it takes practice."

How much does it cost to get started? Expect to spend about $100 at the outset and another $100 to get through the rest of the season. That includes containers, soils, compost teas, amendments and dried fertilizers for four plants, as well as decent scissors for harvesting. An indoor set up, which includes lighting, costs about $1,000, said Bernstein.

Can I plant cannabis in my vegetable garden? Opt for pots instead so if it rains in September, you can bring them inside and set them in front of a south-facing window, Bernstein advises.

"If you leave them out in weeks of rain," he said, "you will just get rotten marijuana."

I've got my starter plant. Now what? Transplant it into a plastic or cloth pot, using a soil mix formulated for cannabis. Leave it in the shade for two to four days before introducing it to sunlight over the course of a week, a process called "hardening off."

Don't overwater. Giving the plant too much water and too much fertilizer are common mistakes. The soil should be pretty dry before you water. Expect to water more frequently as the plant grows.

Feed the plant a compost tea every 10 to 14 days. And about three to five weeks after planting, Bernstein recommends adding a "top dressing" of nutrients and fertilizer. He suggests adding those nutrients every week or two after that.

What about rain? Whether you grow healthy plants with a decent crop depends largely on weather, said Bernstein. A couple of rainy days in early fall can lead to moldy flowers.

"If we have no rain through September, I think everyone will do great," he said.

If it's an especially damp September, harvesting early is a possibility. The flowers won't be as potent, which may appeal to new cannabis consumers.

Early harvests produce flowers that "don't smoke as nice, they don't taste as good," he said. "They are typically a little harsh."

Instead of smoking them, he suggested using flowers from an early harvest to make brownies or other baked goods.

Will it smell? Yes. The plant will have that unmistakable odor as it approaches harvest.

"People who don't like marijuana are going to have to accept that the city will only smell for a month if you are growing outdoors," Bernstein said. "It's going to stink. But at this point everyone is going to be doing it."

When will I know it's time to harvest? If you get a starter plant from a grower, ask about its flowering time, said Bernstein. Those periods generally range from 45 to 70 days. Strains such as Cinex and Blackberry Kush, both widely available and popular in Portland, have 55 and 60-day flowering times. Take note of when the plant's first flowers form and harvest at the end of the flowering time.

Some growers don't put much stock in flowering times and instead look for subtle changes in the plant's appearance to know when to harvest. The calyx swells, pistils change color and recede and the trichomes also change color and develop a mushroom-shaped appearance when the plant is ready to harvest.

"This is where you get debate among experienced growers about what milky color is the perfect color of ripeness," he said.

Time to harvest. Cut down the plant and hang the stems upside down for five to seven days. Once you can easily snap the flowers off the stems, they're ready to be trimmed. Stash dried flowers in a glass or plastic container for about 10 days, opening and closing it every couple of days to allow an exchange of air.

How much will I get from an outdoor plant grown in Portland? Hard to say. A novice grower can get expect at least two ounces from an outdoor plant. (A rookie growing indoors can probably get a half-pound every 60 days; an experienced grower can get up to 2 pounds, Bernstein said.)

Keep expectations low. Experienced cannabis growers focus on maximizing yield and appearance of their flowers. Likewise, Oregon connoisseurs are accustomed to premium marijuana. But one year of growing outside in the northern Willamette Valley isn't likely to turn you into a master grower with a high-grade crop, said Bernstein.

"We are just trying to get people to a successful crop as oppose to something that maximizes yield," he said. "We think most growers will be tickled pink that they can put some cannabis in their yard."

-- Noelle Crombie