When to Plant What

The only two dates that matter: last frost and first frost

Every planting question I've been asked in 35 years — "Is it too early for tomatoes?", "Can I still put in a tree?", "When do the tulips go in?" — comes back to two dates: the average last spring frost and the average first fall frost. Everything you plant is timed off one of those two anchors. Learn yours and you'll never guess again.

Your USDA hardiness zone (that 3 to 10 number) is really a winter-cold rating, but it tracks closely with your frost dates, which is why I use it as the shorthand. Zone 6 here in the Northeast means a last frost around mid-April and a first frost around mid-October. Zone 4 up north loses a full month on each end; Zone 8 down south gains one. The table further down gives you the averages — and the live calendar below it pulls the timing for your exact zip code.

Soil temperature beats the calendar every time

The calendar says May; the soil says no. Plants respond to soil temperature, not what month it is. Cool-season crops (peas, spinach, lettuce, broccoli, onions) will germinate and grow in 45–50°F soil. Warm-season crops (tomatoes, peppers, beans, squash, basil) sulk, rot, or stall until the soil holds 60–65°F — and peppers really want 70°F.

A $10 soil thermometer from the hardware store is the best gardening tool nobody buys. Push it 4 inches into the bed at 9am for three mornings in a row. If it reads 60°F+, the warm-season crew can go in. No thermometer? Watch the plants that never lie: when forsythia blooms, cool-season seeds go in. When lilacs are in full bloom, it's warm enough for beans. When the oak leaves are the size of a squirrel's ear, tomatoes can go out. Old-timers' rules, still dead accurate.

Cool-season vs warm-season: the two teams

Team Cool goes in first and comes out first. Peas, spinach, lettuce, radishes, kale, broccoli, cabbage and onion sets can be planted 4–6 weeks BEFORE your last frost — they shrug off a freeze and actually taste better for it. They bolt or turn bitter once summer heat arrives, so they get a second season in late summer for a fall harvest.

Team Warm waits for the all-clear. Tomatoes, peppers, cucumbers, zucchini, beans, corn, basil and every summer annual in the garden center go in after the last frost date AND when nights stay above 50°F. One 34° night doesn't kill a tomato, but it sets it back two weeks — so the gardener who waits until late May in Zone 6 usually harvests before the one who rushed in early May. Patience is a fertilizer.

Trees and shrubs: fall is the secret season

Here's the thing the big-box stores never tell you: the best time to plant a tree or shrub is September into October, not spring. In fall the soil is still warm (roots grow like crazy), the air is cool (no heat stress), and autumn rains do your watering. That new maple spends all winter quietly making roots underground, then explodes into growth in spring — a full season ahead of one planted in May. Fall-planted trees also cost less, because nurseries are clearing inventory.

Spring is a fine second choice — April in most zones, once the ground is workable — as long as you commit to watering every week through summer. The one time I beg you NOT to plant woody plants is July and August in a heat wave. I've replaced more July-planted arborvitae than everything else combined. Cool zones (3–4): finish fall planting by mid-September so roots grab hold before the ground freezes. Warm zones (8–10): your window runs November right through February, when the plants are dormant and the heat is gone.

Whichever season you plant, the rule is the same: water deeply once a week for the first TWO summers, mulch 2–3 inches (off the trunk), and skip the fertilizer the first year — you want roots, not leaves.

Bulbs, perennials, garlic and the bare-root crowd

Spring bulbs — tulips, daffodils, hyacinths, alliums — need a cold winter to bloom, so they go in the ground in October, once soil drops below 55°F and before it freezes solid. Plant them 2–3 times as deep as the bulb is tall, pointy end up. Garlic follows the same October rule (November in Zones 8–9): a single clove planted in fall becomes a full head next July.

Perennials are flexible: plant them in spring (April–May) or early fall (September). Avoid the dog days — a coneflower planted in July spends all its energy just staying alive. Bare-root roses, fruit trees and shade trees are the exception that proves the rule: they're planted dormant, in late winter — January in Zones 8–10, March–April in colder zones — before they wake up.

Your zone's planting calendar

Enough theory. Type in your zip code and the calendar below pulls the planting, seed-starting and bulb tasks for your USDA zone straight from my Seasonal Planner — month by month, for the whole year. The current month is highlighted so you know what to do this weekend.

Linda's planting windows by zone