Clean and sterilize the pot if it has been used for other plants. Scrub it in hot, soapy water, rinse it and then soak it for half an hour in 1 cup of bleach combined with 1 gallon of water. Rinse it again and allow it to dry before planting.
Fill the pot to within 1 inch of the rim with equal parts of compost and a sterilized potting mix. Water the soil until water runs from the bottom of the pot. The soil will most likely settle, so add more until it is within an inch of the top of the pot.
Sow the radish seeds 1/2 inch deep and one inch apart. Place the first seed in the middle of the pot and then space the others, in concentric circles, around it. Keep the soil moist and the radishes should sprout within one week.
Water the radishes when the top of the soil is dry, until the water runs from the bottom of the container. Soil dries out quicker in windy areas so pay close attention to the moisture content.
Fertilize the radish plants with a 21-0-0 fertilizer when they have their second set of leaves. Apply the fertilizer at the rate suggested on the package for container-grown plants.
Move the radish pot to a sheltered location when the winds are particularly strong.