Early spring brings us a lot of yellow—forsythias, daffodils—and we're grateful, but in our test gardens, we know that spring has truly arrived when low mounds of white and blue moss phlox start their show. A classic color combination (think Delft pottery, hyacinths, even the sky), these diminutive blue and white flowers give the garden a fresh promise of the warmer days and fragrant nights to come. The fact that they create dense mats of rugged ground cover that look great for the rest of the season is an added benefit. Like many in early spring, we crave masses of color, not just a dash here or there. In that spirit, we created this value-priced selection of six moss phlox plants of our choice, three white and three blue, to encourage indulgence. Phlox subulata