When she washes her hair, Vicki Parsons rinses with neem tea to control the grays. She pours it over her dogs' food and then brushes her teeth with a powder made from neem bark. "I have very little gray hair. I live with 16 dogs on 2 1/2 acres, and I do not have fleas. I'm the first generation on my dad's side to have all my own teeth at age 60," she says. "My periodontist is amazed."I know plenty of gardeners who rely on neem — Azadirachta indica, an India native — as a natural, non-toxic pesticide. It won approval from the Environmental Protection Agency in 2009 for use on edibles and ornamentals. Fewer of us know neem's long history — 4,000 years! — as a medicinal herb. Which is why I was surprised to see its benefits have been well-documented by the U.S. government's National Institutes of Health.It fights bacteria, viruses and fungus, inflammation, high blood sugar and cancer, according to a 2005 NIH publication. It's a powerful antioxidant that promotes healing in ulcers and discourages damage to genes caused by environmental factors, like sun exposure.If all that doesn't make you want to hug a neem, take note: It's also a quick-growing shade tree. Vicki and her husband, Mac, have been growing the trees in Brandon since 1992, after Vicki developed a painful sensitivity to the chemicals in her rose sprays and doggie flea dip. Neem proved an effective alternative — without the Monday morning chemical hangover. Neem Tree Farms is the largest independent grower in the United States, Vicki says of her company, although they can't possibly produce enough leaves, bark and seeds to become a major supplier for neem products, as they once hoped. At least, not in Brandon."We're too far north," Vicki says. "When it gets really cold, the trees freeze back to the ground. They'll come back if they're heavily mulched (to keep the roots warm), but it can take a while."While that's bad for business, it's no reason not to grow a neem tree for personal use. One is plenty for a homeowner, and if a freeze knocks it out for three months, you won't lose the farm — so to speak. "They're tough, tough trees. I don't know anywhere (locally) they won't grow," Vicki says. Sun-loving neem trees tolerate almost any soil but do best in dirt with plenty of organic matter, like compost. They're drought-tolerant but need watering when young to establish roots, and they're happiest if they get water while growing. They're not good candidates for containers because they have a deep tap root. And they can't survive in mucky, wet soil. Neems most often get their start from seeds, but that can be tricky."The seeds are only viable for about 30 days after they're harvested in the summer. If you buy them in February online, you've thrown your money away," Vicki says. "I fly to Mexico in the summer and pick up seeds, hand carry them so they don't go through radiation, and sell them for 30 days."Along with seeds and seedlings, Neem Tree Farms sells neem products, from bath soaps — good for people with a wide range of skin conditions — to their bestseller, Neem Bark Toothpowder, to help prevent and control gingivitis. Many of the products are manufactured in Mexico and India by women in impoverished communities.No neem products have been approved by the federal Food and Drug Administration for medicinal use. That requires costly clinical trials, which aren't worth the expense for manufacturers since neem has been around too long to be patented. Those who sell neem products must carefully adhere to the FDA's rules about the claims they make, so you won't find words like "cure" or "heal" in their descriptions. But testimonials abound — starting with Neem: A Tree for Solving Global Problems, which was previewed, reviewed and ultimately approved by myriad scientists before its publication by the National Academies Press in 1992.If you want to grow your own neem tree for the medicine cabinet and garden shed, Vicki suggests whacking it back to waist height every spring to maintain a manageable height.As a shade tree, it will do magnificently in southern Pinellas and Manatee counties, growing 60 feet tall. Farther north, it may freeze to the ground and come back as a bush.The easiest way for gardeners to use neem is as a tea. Fill your drip coffeepot with leaves, add water, brew and let simmer. Pour it on your hair — its antioxidant properties are said to help prevent graying — spray it on the plants and pour a cup for your loved ones to boost their immune system and ease aching joints.They may not love you for it at first, Vicki warns."It tastes terrible. You have to learn to like it. But you will."Contact Penny Carnathan at [email protected]; visit her blog, digginfloridadirt.com; join in the chat on Facebook, Diggin Florida Dirt; and follow @Diggin Penny.