If your soil is made of clay or filled with rocks, you're probably going to have a hard time raising long, straight carrots (Daucus carota). These roots require smooth, barrier-free growing room to prevent them from becoming twisted or split. Building raised beds and filling them with quality soil is a great way to get carrots to grow long and straight; building raised beds inside old tires delivers the double bonus of recycling junk along with raising great vegetables.
Cut the entire sidewall from one side of an old tire using a utility knife. Wear heavy work gloves during this part of the task to prevent slicing your fingers. Removing the sidewall increases the usable planting surface space inside the tire.
Place the tire in the garden or yard where it will stay through the growing season. Carrots need full sunlight so find a spot for the tire where it will receive at least 8 hours of sunlight a day. Position the tire with the cut side facing upward.
Make a half-and-half mix of potting soil and compost and fill the center of the tire until the top of the mix is 1 inch below the top edge of the tire.
Draw a circle in the soil mix with your finger about 2 inches inside the outer rim. Draw another circle about halfway between the first circle and the center of the tire. These two lines are the rows for planting the seeds.
Sprinkle the carrot seeds along each of the lines, dropping about 2 seeds per inch. Smooth the top of the soil mix with your hand so that it barely covers the seeds. Water the mix thoroughly.
Water the mix whenever it begins to dry out. Planters lose moisture much faster than gardens grown in the ground, so you may have to water the carrots every day. The carrots begin to sprout in 10 to 14 days.
Thin the carrots to one for each inch when they are about 1 inch tall. After the carrot roots begin to fill out and are about the size of a finger, harvest every other carrot. You'll get a batch of tender fingerling carrots to eat and leave more room for the remaining carrots to grow.
Harvest the rest of the carrots when they are full sized and their shoulders begin to push above the soil.