You can skip thinning if you plant Monopoly seeds three or four inches apart. When you thin other varieties, save any little leaves and tiny beets you pull out and put them in a salad. The roots that remain taste best if harvested by the time the beets are two inches in diameter. For a continuous supply, make your first small sowing this month, then plant a few more beets every two weeks until late summer. Baby leaves of most varieties are ready in about 30 days, nice-sized roots in 60 days.
Beets are notoriously slow to sprout, especially in clay soils.
You can help them along by soaking the seed in warm water for an hour before planting. Also, try planting some radish seeds along with the beets. Radishes mature fast enough that they'll be long gone by the time beets need more space. If leaf miners regularly ruin beet leaves in your garden, spread a floating row cover over your plants to prevent the flies from laying their eggs. Control leaf spot infections by picking off any damaged leaves.