Like all vegetables, radish plants need a good amount of water to grow and produce good sized tasty radishes.
It is important that radishes are planted in well-drained soil. Over watering can be as damaging to the crop as not getting enough water, and sitting in areas that are water logged will mean that the radishes are poor.
Germination time is short, generally 2 - 4 weeks, therefore it is vital to get growing conditions perfect straight away as there is very little time to correct any mistakes. Luckily, it is relatively easy to get right. They do not require much space- about 1 inch apart should do it. They do need sun though, so try to make sure they are not in area which is too shady. And keep an eye on crops planted in the hot summer months to make sure they have plenty of water.