When watering radishes, it's important to give them a steady, consistent supply of water throughout their growing season. Unlike other vegetables, radishes don't need an occasional deep soak. They do much better with several shallow waterings per week.
It is important to remember that radishes have a fairly high water content. They much prefer growing in a consistently damp soil environment, rather than one where the soil dries out and then gets inundated with water again, before drying back out. Cycles like this can cause the radishes to crack. And if the soil stays too soggy for too long, the radishes may even rot before reaching maturity.
Radishes grow so fast that they usually aren't bothered by pest or diseases problems. Overhead watering is acceptable, as are soaker hoses or drip irrigation systems. The main thing is to keep the soil evenly moist. In our garden, we often just use an old watering can to irrigate our radish patch. Radish plants can certainly handle a light watering 4-5 times per week, just make sure the soil doesn't become too soggy. A great way to keep the soil moist is by mulching with grass clippings, straw or strips of newspaper. Sawdust is fine as well, as long as you know where it comes from and doesn't include remnants from pressure treated wood.
In most cases, it's not a good idea to fertilize radishes. You can work some organic material or fertilizer into the soil a couple of weeks before planting if you are worried about the quality of your soil. We usually work in some composted manure to the soil in our garden anyway, and we don't purposefully keep it away from where we're going to plant our radishes. In most cases, commercial fertilizer products can have a negative effect on radishes and can cause them to be quite woody. Additionally, radishes grow so fast that they don't have time to absorb much fertilizer before they are ready for harvest.
By now, your radishes should be starting to poke out of the soil and may be getting close to be ready for harvest. Click on the following links for more information...