Research linking vitamin D to an increasingly long list of health benefits is pouring out of universities and flooding medical journals, some associating adequate vitamin D levels to a lower risk of developing certain cancers, a higher chance of surviving cancer, and increased protection against diabetes, infections, heart disease, and perhaps even dementia. Our body can manufacture the substance when the sun strikes our skin in ideal conditions, but most Americans are dreadfully deficient in this superstar substance. That's because much of the country doesn't get enough year-round sunshine. And because we wear so much sunscreen to protect against skin cancer—a sensible precaution, but one that blocks natural vitamin D production.
THE DETAILS: It's hard to get what experts say is a reasonable vitamin D target, 1,000 to 2,000 International Units (IU) a day, from food. But one potent source of vitamin D is often overlooked: the shiitake mushroom. These mushrooms have long been used medicinally in Asia (some studies have found the fungi to hold antitumor properties). But many shiitake mushrooms you'll find at the supermarket are grown in sawdust, not on logs, as nature intended, so they don't have as many nutrients as they should. And while log-grown shiitakes go for up to $40 a pound in Japan, you can enjoy their superior flavor and increase your nutrient intake by growing your own at home.
Rusty Orner, owner of Quiet Creek Herb Farm and School of Country Living with his wife, Claire, shared his mushroom expertise at the Pennsylvania Association for Sustainable Agriculture's 19th Annual Farming for the Future conference. While most participants in the room were farmers, serious gardeners, and/or sustainable-food advocates, the truth is, growing shiitake mushrooms in your yard isn't very difficult.
Here's what you need to know about growing shiitake mushrooms at home.
• Find your logs. If you have trees on your property, you can use logs or branches from freshly cut, living hardwood trees (white, red, or pin oak; sugar maple; or ironwood). Ornel says it's best to cut between October and April because that's when the moisture content is ideal. The logs should be three to eight inches in diameter. You can also find suitable logs from timber stand improvement cuts. Cut the wood into three- to five-foot sections. These will be the logs your mushrooms will grow from for the next five to nine years, if you do things right.
Read on to find out how to select your spawn.
• Select your spawn. To grow shiitake mushrooms, you do need to make a one-time investment in spawn, which is fungus tissue used to propagate mushrooms. Ornel trusts family-owned Field & Forest Products. Spawn comes in different forms, such as wooden dowels called plugs, and in sawdust and grain mixes, but the easiest for beginners is the plug method. It's best to inoculate your cut logs within two weeks of cutting, to prevent fungal infection, so time your cutting according to your weather.
• Drill diamonds. Once the temperature in your area is consistently above freezing at night, it's time to drill holes into the wood with the drill bit size indicated in the instructions that came with the spawn plugs. "You drill, inoculate, and seal all in one day," explains Joe Krawczyk, owner of Field & Forest Products.
Keeping a two-inch margin at the top and bottom of the log, drill holes in a diamond pattern, with the top and bottom of the diamond six to eight inches apart, and the diamond's sides about an inch apart. You can make as many diamonds as you can fit on the log. Fill the holes with your plugs according to the instructions, and seal with cheesewax or beeswax heated until it just turns soft. You can heat the wax on the stovetop in a double boiler, or in a pot within another pot partly filled with water. Take it off the heat as soon as it's soft, because wax is flammable. Avoid paraffin waxes because they don't work as well and are laced with toxic chemicals. You can also buy the plugs in a kit that includes wax.
• Stack 'em up. The same day you inoculate, take your logs outside and lean them in an area that receives half sun/half shade. Ornel says propping them under white pine trees is a perfect environment. Expect the fruit to pop out eight to 16 months after inoculating; check frequently as the fruiting time approaches. Once they pop, the window of opportunity for harvesting the mushrooms is only about a week. If everything goes as planned, each log could produce a pound to a pound and a half twice a year.
• Give them a thump. After the first full year, you can thump your logs during spring, summer, or fall to induce production. "I've been doing this 30 years, and it works," says Krawczyk. To thump, simply pick up the vertical log and let it slide down so the bottom slams into the ground. This movement, particularly if done when rain is in the forecast, seems to spur growth. Lore also has it that doing this causes thunder, so don't overdo it.
• Pick only the right mushrooms. Since some mushrooms are poisonous, it's important to be sure of what you're harvesting off your log. The good news is, most poisonous mushrooms don't grow on logs, and shiitakes have a distinctive look: Their main characteristics are a white stem with gills that are not directly attached to the stem. The gills are tightly packed, explains Krawczyk. The mushroom cap is brown to black, depending on humidity. You also want to make sure the mushrooms you harvest are sprouting from your inoculation sites, not elsewhere on the log. At any rate, it's a good idea to invest in a good mushroom guide with color photos to make sure what you're picking is a shiitake.
• Eat fresh or dry, but either way, enjoy. A fresh shiitake boasts about 100 IU of vitamin D per gram, but if you dry it in the sun, it creates 10,000 IU. If you dry it upside down in the sun and let the gills absorb the sun, a gram will provide 20,000 IU. The mushrooms are so full of D, in fact, it's important not to eat too many dried shiitakes; vitamin D overdose can occur with chronic consumption of 40,000 IU of vitamin D per day. No matter what you eat, it's a good idea to ask your doctor for a simple vitamin D blood test to figure out if you're getting enough (or too much, although that's usually not the case) of a good thing.
The mushrooms take about two days to dry, but you should bring the mushrooms in at night so the dew doesn't dampen them. You can store them in a glass jar in a dark place for up to a year, says Ornel. To revive a dried shiitake, soak it in water for 30 minutes, or add the dried mushrooms to soups.