How are the frost dates calculated?

We pull ten years of daily low temperatures for your zip code's coordinates from the Open-Meteo historical weather archive and record, for each year, the last spring day and first fall day at or below 36°F, the air temperature at which frost usually forms on the ground and on leaves. The average is your typical light-frost date; we also show the latest spring and earliest fall frost in that period so you can see the risk. Treat the dates as a guide and watch the forecast.

Why does soil temperature matter more than air temperature?

Roots grow and seeds germinate based on soil warmth. Most native perennial plugs establish well once soil at planting depth is above about 50°F, and many seeds need 60°F or more. Air can be 70°F on an April afternoon while soil is still 45°F.

When is the best time to plant native perennials?

The six weeks after your last frost and the six weeks before your first frost. Spring gives the longest first season; fall gives cool soil, reliable rain, and less watering. Midsummer planting works only if you water weekly.

Should I really leave dead stems up all winter?

Yes. Coneflower and black-eyed Susan seed heads feed goldfinches, hollow stems house small carpenter bees and mason bees, and leaf litter shelters overwintering butterflies and moths. Cut back in spring once daytime highs hold above 50°F for a week.

Zip code tool

Garden Calendar

What should a native gardener do this week, right here? Enter a zip code for your frost dates, a planting and pollinator forecast built on soil temperature, this season's task list, and what is blooming and setting seed near you.

Pests and invasives to watch for in Sep

no rights reservedTree-of-heaven · Seed clustersBig drooping clusters of twisted, papery, tan-to-red samaras on female trees, persisting into winter.Story, harm, and what to do →
(c) Link Davis, some rights reserved (CC BY-NC)Japanese knotweed · FloweringSprays of tiny creamy-white flowers, buzzing with bees.Story, harm, and what to do →
(c) Fyodor Pudovikov, some rights reserved (CC BY)Mile-a-minute weed · Blue berriesClusters of metallic blue berries sitting in the leafy cups.Story, harm, and what to do →
(c) jenna_medlar, some rights reserved (CC BY-NC)Oriental bittersweet · Orange berriesYellow-orange capsules along the stems splitting to show red seeds, unmistakable after leaf drop.Story, harm, and what to do →
(c) sureetb, some rights reserved (CC BY-NC)Purple loosestrife · Seed spikesBrown spikes shedding dust-fine seed, up to two million per plant.Story, harm, and what to do →
(c) Sequoia Janirella Wrens, some rights reserved (CC BY-NC)Garlic mustard · RosettesLow rosettes of kidney-shaped, scalloped leaves that smell of garlic when crushed. They stay green all winter, which makes them easy to spot.Story, harm, and what to do →

Monarchs this month: Caterpillars

Yellow, black, and white banded caterpillars up to 2 inches with two pairs of black filaments. Chewed leaves and dark frass on the leaf below give them away.

Plant more milkweed if they run out; do not move them indoors unless you know how to raise them cleanly.

Monarch tracker →

Season · Long Island default frost dates

Fall planting window

Cooling soil and reliable rain make this the second-best planting season, and the biggest seed harvest.

1Plant perennials, shrubs, and trees at least six weeks before your first frost so roots establish.
2Collect coneflower, bee balm, milkweed, blazing star, and beardtongue seed; let goldenrod and asters finish first.
3Direct sow fresh seed of species that want fall sowing (garden phlox, wild geranium, black cherry pits).
4Watch the monarch migration on north-wind days; goldenrod and seaside asters are the fuel stops.
5Rake leaves onto the beds as mulch instead of bagging them; many moths overwinter in them.
6Divide and move spring bloomers (phlox, columbine, golden Alexanders) now.

Showing the task list for an average Long Island season (April 15 to November 9). Enter a zip code above for your own frost dates, forecast, and local observations.

FAQ

Timing questions

How are the frost dates calculated?: We pull ten years of daily low temperatures for your zip code's coordinates from the Open-Meteo historical weather archive and record, for each year, the last spring day and first fall day at or below 36°F, the air temperature at which frost usually forms on the ground and on leaves. The average is your typical light-frost date; we also show the latest spring and earliest fall frost in that period so you can see the risk. Treat the dates as a guide and watch the forecast.
Why does soil temperature matter more than air temperature?: Roots grow and seeds germinate based on soil warmth. Most native perennial plugs establish well once soil at planting depth is above about 50°F, and many seeds need 60°F or more. Air can be 70°F on an April afternoon while soil is still 45°F.
When is the best time to plant native perennials?: The six weeks after your last frost and the six weeks before your first frost. Spring gives the longest first season; fall gives cool soil, reliable rain, and less watering. Midsummer planting works only if you water weekly.
Should I really leave dead stems up all winter?: Yes. Coneflower and black-eyed Susan seed heads feed goldfinches, hollow stems house small carpenter bees and mason bees, and leaf litter shelters overwintering butterflies and moths. Cut back in spring once daytime highs hold above 50°F for a week.

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