Microgreen Seeds
Mesclun seed mixes are a good choice for microgreens: Varieties like Paris Market Mix and Asian Baby Leaf Mix from Renee's Garden (reneesgarden.com) contain a blend of greens selected because they tend to sprout at the same time. Single-crop microgreens also work. Scatter the seeds over the soil surface, then place the cardboard over the seeds and lightly press them into the soil.