If you're like me, and can't wait until after Mother's Day to plant your garden, radishes are a good bet. Soil temperatures only have to be 40 degrees in order for them to succeed.In that same "impatience" vein, radishes are a great choice for gardening with children! They sprout in as little as five days, and are ready for harvesting in as little as 25 days. These lovelies are french breakfast radishes. In the still chilly spring weather, I sped things along by heating up the planting area with victorian bells. You can do the same thing by putting a sheet of clear plastic over the plant bed, and weighting it down with rocks until you have sprouts.