Zone 4 Warm-Season Crops to Start After Memorial Day

May 23, 2026

Zone 4’s Frost-Free Date: Why Memorial Day Is Your Go Signal

Zone 4b clears its average last frost around May 15–25. Zone 4a pushes that window to May 25–June 1. Memorial Day weekend lands right inside that range: air temps are reliably frost-safe and soil in a south-facing raised bed reads 55–60°F by afternoon.

If you’re in Zone 4 and want the full frost-date math alongside a month-by-month planting calendar, the Northeast Vegetable Gardening guide at GBZ was written for this exact window.

That 55–60°F soil reading is the number that drives everything below. Warm-season crops need soil at or above 60°F to germinate reliably and to transplant without shock. Below that, seeds rot and transplants stall rather than establish. Check with a probe thermometer 3–4 inches down, morning or late afternoon, on three consecutive days before planting.

What “Cold-Hardy Warm-Season” Actually Means

The phrase describes crops that tolerate soil in the 55–60°F range and brief nights near 45°F without dying, but will still collapse at a frost. Tomatoes, cucumbers, and summer squash belong here. They are not cool-season crops like kale or peas; they simply have a wider thermal floor than eggplant or sweet potatoes.

Warm-Season Crops You Can Start in Zone 4 Right Now

Tomatoes and peppers. Both go in as transplants, not direct-sown seeds, this late in Zone 4. If you started seeds indoors 6–8 weeks ago, those seedlings are ready. The gate for peppers is nighttime temps above 50°F; a frost cloth on the first two weeks of nights below that saves you weeks of stunted growth. Choose determinate tomatoes or varieties with 60–70 day maturity for Zone 4’s compressed season.

Cucumbers and summer squash. Direct sow or transplant both now. Sixty degrees in the soil is the floor; seeds sown in cold soil rot before they sprout. Space cucumbers 12 inches apart in rows, or set 2–3 seeds per hill and thin to one. Zucchini is the most forgiving entry point for Zone 4 growers: expect first harvest 45–50 days from transplant once soil warms.

Beans and corn. Bush beans germinate at 60°F and are among the cleanest direct-sow crops for post-Memorial Day planting in Zone 4. Sow 1.5 inches deep, 3 inches apart in rows. Sweet corn needs a block of at least 4 rows for adequate pollination; space seeds 9–12 inches. Both crops complete well within Zone 4’s 90–130 frost-free day window across sub-zones when sown now.

For a side-by-side look at what’s moving across all zones this month, the May planting guide by USDA zone has the full regional breakdown.

What to Wait On: Crops That Need Soil Above 65°F

Several warm-season crops are regularly oversold for early-June planting in Zone 4 because they are warm-season in name but need soil at 65–70°F rather than 60°F to perform.

Eggplant. Soil below 65°F causes purple-leaf stall and suppressed fruit set. Even when air temps cooperate, planting before soil consistently reads 65°F costs 2–3 weeks of effective growth. In Zone 4, that delay can push harvest past the first fall frost. Wait until mid-June, or pre-warm the bed with black plastic mulch for 10 days before transplanting.

Watermelon and cantaloupe. Both want 70°F soil and 90–100 frost-free days. Zone 4a has roughly 100–120 frost-free days in a good year, so watermelon is borderline. If you attempt it, start with transplants rather than direct sow and hold until June 5–10.

Sweet potatoes. These need sustained soil warmth above 65°F and a long season (90–120 days). They are marginal in Zone 4 without black plastic and a heat-amplifying site. Most Zone 4 growers get better return from winter squash planted now.

Okra. Germination fails below 65°F, and okra needs 60 or more days of real heat to produce meaningful yield, making it a poor fit for Zone 4 without a cold frame or season-extending row cover.

June Follow-Up: What to Direct Sow Next

Zone 4’s short season rewards succession planting. If transplants go in this weekend, plan a second round of bush beans on June 10–15 for a staggered harvest through August. Winter squash (butternut, acorn) should go in by June 1–7 at the latest: both need 75–100 days and Zone 4’s first fall frost arrives by late September in most sub-zones.

Basil is the warm-season herb to hold back. It blackens at 45°F nights and sulks at soil below 60°F. Wait until the first week of June, when Zone 4 nights are reliably above 50°F.

To see how Zone 4 timing stacks up against one zone south, the Zone 5 Memorial Day planting guide shows the same crops going in 2–3 weeks earlier, which clarifies exactly which varieties are worth the extra patience in Zone 4.

See the full Zone 4a and Zone 4b planting calendars for frost-date ranges and month-by-month sequencing.

---