Here are my tips for growing great radishes:

Site, soil type:

Radishes like moderately fertile soil.

Grow in loose well-drained soil.

Grow in full sun.

Planting requirements:

Radishes can be planted at 40 degree air temperature or three weeks before last frost.  They grow best at 50-65 degrees.

Plant seeds ½ inch deep in rows eight inches apart.  Thin seeds to three inches apart after they emerge.

Nutrition/Fertilizer needs:

Apply fertilizer that is low in nitrogen and high in phosphorus like rock phosphate.  Rock phosphate is available to the plants faster than bone meal (which is also high in phosphorus).

Water needs:

Keep moist.  Radishes will be more mild if they are consistently moist.

Other tips:

Harvest before they become too large. This will help to avoid splits and hot or pithy radishes.

Control flea beetle damage (small holes in leaves) with silver mulch or lightweight row cover, or with a rotenone-pyrethrum spray (which is organic.)

Try letting some radishes go to seed.  They will produce pods.  Pick when they are ½ inch long for a crunchy mild snack or salad addition.

Some companies sell seeds specifically for growing as pods.