You can start planting radishes earlier than a lot of other vegetables. The seeds can be sown directly into a container or the ground 2-3 weeks before the last expected hard frost in your area. They will tolerate cold nighttime temperatures quite well. In many areas, a fall crop can also be planted about 6 weeks before the first expected autumn frost.
Make sure the soil is tilled to about 4 inches deep. Using a hoe, create rows that are about 1/2 inch deep. If planting more than one row, space the rows at least 6 inches apart. If planting more than 2 rows, we prefer to space a few of them at least a foot apart just so it makes it easier to walk around in the radish patch and harvest.
Once the rows are created, drop the seeds in, sowing them to where there are about 6 seeds evenly spaced per linear foot. Cover the seeds with 1/2 inch of fine soil and water them in well. If you are also planning to grow carrots, consider planting them at the same time as you plant the radishes. Just mix the seeds together and sow them evenly in the same row. The radishes seeds will germinate quite quickly. About the time the radishes are ready for harvest, the carrots will be starting to sprout.
After the radish seedlings emerge in about 1 week, thin to 1 seedling every 2 inches. At this point, you can apply a thin layer of mulch, which will help keep the soil moist.
If growing radishes in a container, fill it with a good quality top soil or garden soil mixture. Make sure there are adequate drainage holes in the bottom of the container. The container can be any size, but needs to be at least 4-6 inches deep. Instead of creating rows, you can just poke the seeds into the soil about 1/2 inch and cover them with loose soil. Space the seeds evenly about 2 inches apart and water them in well after planting.
Now that you are done planting radishes, the next step is to make sure to keep the plants evenly moist...