giant radish take to grow full 60-75 days and even longer. Small radishes are the ones which take only 25-35 days.

Try hydroponics! I've never heard of giant radishes grown this way, but they're supposed to grow much faster.

eh, i do a lot of work with hydroponics and it grows a little bit faster but not anywhere close to twice as fast. if your interested come check out the hydroponics forum here on GW. ~Ryan "the hydroponics master"

Here is a link that might be useful: some of my hydroponics

root crops usually don't grow well if they are not grown in soil.