How Deep Do You Sow? Increase germination rates by planting seeds at the correct depth. As a rule, seeds should not be buried any deeper than their diameter. Forget the quarter-inch planting depths you see on many seed packets. That's too deep for all but the biggest seeds, such as peas and beans. Some seeds even need light to germinate—don't bury those at all. Cover these seeds: Beets Broccoli Cabbage Cauliflower Celery Chard Cucumbers Melons Onions Parsley Peas Radishes Spinach Sow these seeds on top of the soil for best germination: Ageratum Astilbe Balloon flower Cleome Coleus Coreopsis Dill Impatiens Lettuce Mexican sunflower (aka tithonia) Ornamental peppers Petunias Savory Shasta daisy Snapdragon Strawflower Stock Sweet alyssum Yarrow