Seeds

The 'Average Last Frost Date' Has a Coin-Flip Chance of Being Wrong

Planting exactly on the average last frost date means, by the statistic's own definition, a roughly 50% chance frost still comes.

Frost date calculators report the date at which the historical probability of frost drops to 50%, based on decades of local weather data. That's a median, not a guarantee — it's the date half of past years had their last frost before, and half had it after. Treating it as a hard planting deadline builds in even odds of a frost event on tender transplants.

Risk-averse gardeners plant using the date associated with a 10% or even 5% frost probability instead, which typically falls one to three weeks later than the 50% average date depending on region. The trade is a shorter growing season against real insurance against a late cold snap.

Put this into practice

More facts like this

Old Seed Is Usually Still Good — But Not All Species Age AlikeSeed longevity varies from about one year (parsnip, onion) to ten or more (tomato, cucumber) under the same storage.
Leggy Seedlings Are a Light Problem, Not a Watering ProblemThe classic pale, stretched, floppy seedling is almost always starved for light intensity, even when it's sitting right in a bright window.
The Bulb Depth Rule Is a Ratio, Not a Fixed NumberUsing one fixed planting depth for every bulb ignores that the standard rule is a multiplier of bulb size, not a single number.