The gardening world is almost totally controlled by the weather conditions. We can fertilize, till, mulch, transplant, etc., only when Mother Nature allows us to. Assuming you live in a colder climatic zone, not much of a risk with that assumption when you ask a question about frost, the frost in the soil will keep you from doing any tilling or transplanting, or planting for that matter.

Depending on the length of winter temperatures and the amount of ground cover, frost depths easily reach 2 feet or more in depth. The depth of the frost and the amount of warm temperatures makes predicting an average date when all the frost leaves the ground is a very difficult task. That is why most gardeners test the soil with a shovel or spade when they think it has been warm enough for a definitive period of time. If the spade hits a frost layer when attempting to dig, you will know immediately. Wait another week or so and try again. If the frost band was narrow, waiting a week may be enough to begin the process of gardening.

A general frost free date for soil for zone 5 residents, with a normal winter, would usually occur in March or early April. Zones 1, 2, 3, and 4 would be frost free later in April and May.