Dry horsetail leaves by placing them between two paper towels and putting them in the microwave. Set the microwave on low or medium heat. Start with two minutes on the timer. Test the horsetail leaves to see if they are beginning to dry. Repeat this in two-minute intervals until the leaves are dry and brittle. If you prefer to use a conventional oven, spread the horsetail leaves on a cookie sheet and place it in the oven on low heat, about 250 degrees, for 15 minutes. Check the leaves every few minutes to make sure they roast but do not burn. After 15 minutes, if the leaves are still pliable, put them back in the oven for five-minute intervals until they are completely dry.
Put the dried leaves in a cast-iron skillet on high heat. Continuously stir with a wooden spoon until the leaves resemble powder or flour.
Store the horsetail powder in a glass jar until you are ready to dilute it in water to soothe an upset stomach, make tea, apply to skin infections or use for a myriad of natural remedies.