Delaware Planting Guide: What to Grow and When

Delaware may be the second-smallest state in the country, but its position on the Delmarva Peninsula creates a climate warmer and more moderate than its latitude suggests. The Chesapeake Bay to the west and the Atlantic Ocean to the east both temper temperature extremes, stretching Delaware’s frost-free season well beyond what inland mid-Atlantic states at the same latitude experience. A gardener near Rehoboth Beach can reasonably count on more than 230 frost-free days — a figure that puts southern Delaware closer to Virginia than Pennsylvania in practical growing terms. This Delaware planting guide covers frost dates by county region, a month-by-month planting calendar, the crops that consistently perform across the state, and the summer heat and humidity challenges that require active management every season.

What makes Delaware particularly useful for gardeners is its manageable scale. Unlike sprawling states where regional adaptation is genuinely complex, most Delaware gardeners need to understand just three zones — the northern piedmont, the central coastal plain, and the warmer southern shore — to build an accurate planting calendar. The University of Delaware Cooperative Extension [1] has documented these regional patterns through decades of trial work, and the frost date and soil differences are consistent enough to plan around reliably across the state’s roughly 100-mile length.

Understanding Delaware’s USDA Hardiness Zones

Delaware spans USDA Hardiness Zones 6a through 7b, covering approximately 15°F of variation in average annual minimum temperature from the northern piedmont to the southern Atlantic shore. This range is smaller than mountain states, but it has real consequences for perennial winter survival, spring planting timing, and how long the fall season extends before killing frosts arrive.

Northern Delaware (New Castle County): Wilmington, Newark, and New Castle fall in Zones 6a–6b. Positioned at the edge of the Appalachian piedmont, this region sits slightly farther from the ocean’s moderating influence and experiences colder winters than the rest of the state. Last spring frosts typically arrive April 10–15; first fall frosts come around October 28–November 2. Northern Delaware gardeners average 196–205 frost-free days — generous by mid-Atlantic standards, but measurably shorter than zones further south.

Central Delaware (Kent County): Dover, Milford, and the surrounding coastal plain fall in Zone 7a. Flat topography reduces cold-air pooling, and Atlantic moisture systems move freely through this region. Last spring frosts average April 5–10, with first fall frosts arriving November 1–5. Central Delaware gardeners can rely on 205–214 frost-free days in a typical year.

Southern Delaware (Sussex County): Georgetown, Lewes, Rehoboth Beach, and the lower Delmarva Peninsula reach Zones 7a–7b. Atlantic Ocean proximity significantly moderates temperatures — coastal stations rarely drop below 15°F even in hard winters. Last frosts average March 28–April 5; first fall frosts typically don’t appear until November 8–12. Sussex County’s 218–232 frost-free days approach upper-South growing seasons, enabling crops like sweet potatoes, okra, and figs in sheltered spots.

Delaware is among the mid-Atlantic states seeing measurable shifts in frost timing. Recent decades have pushed last spring frosts earlier and first fall frosts later across much of the region. Our guide on climate zone migration covers how these shifting USDA hardiness zones are changing what mid-Atlantic gardeners can now grow and when.

Delaware Frost Dates by Region

Frost dates are the foundation of any Delaware planting guide. The figures below draw on historical climate data compiled through the University of Delaware Cooperative Extension [1]; these represent 50% probability dates, meaning half of all years see frost before or after these averages. For heat-sensitive crops like tomatoes and peppers, using 10% probability dates — which run approximately two weeks later in spring and two weeks earlier in fall — provides a meaningful safety margin before committing transplants to the open ground.

The practical implication of these regional differences is most visible in spring startup timing. A Lewes gardener can direct-sow peas in early March and has a realistic shot at broccoli transplants going out in late February under row cover. A Wilmington gardener doing the same thing is gambling — a late-March frost would kill uncovered transplants. The roughly 18-day difference in last spring frost dates between northern and southern Delaware sounds modest, but it represents real risk at the transplant stage and real opportunity at the harvest end of the season.

One local nuance worth knowing: Delaware’s flat terrain means cold-air drainage — the tendency for cold air to pool in low spots — is less pronounced than in hilly regions. However, low-lying areas near wetlands or tidal creeks, and gardens in field bottomlands, can still experience localized frosts a week or two earlier in fall than surrounding higher ground. If your garden sits near standing water or a drainage ditch, add a buffer week to your expected first fall frost date.

Delaware Planting Calendar: Month by Month

The calendar below covers Delaware’s three primary growing environments: northern Delaware (Wilmington/Newark area, Zone 6b), central Delaware (Dover area, Zone 7a), and southern/coastal Delaware (Georgetown/Lewes area, Zone 7b). Adjust based on your specific frost dates from the table above.

Delaware’s calendar has one structural feature that distinguishes it from states with harder winters: the spring-to-summer transition happens quickly once it arrives. After last frost, nighttime temperatures in Delaware climb rapidly, and warm-season crops like tomatoes and peppers take off without the slow warm-up that limits gardens in cooler northern states. The flip side is that the cool-season window — when lettuce, spinach, peas, and broccoli are at their best — closes quickly as June heat and humidity build. Timing cool-season crops to finish before mid-June in northern Delaware and before late June in the south is the key to quality harvests rather than bolted, bitter greens.

The fall window reverses this dynamic and is often Delaware’s most productive season. From late August through October, falling temperatures improve flavor in brassicas and root vegetables, pest pressure drops dramatically, and the workload lightens. Gardeners who invest in a fall succession — starting brassica transplants in late June or early July, direct-sowing spinach in August — typically harvest some of their best produce of the year. The seasonal planting guide covers spring and fall successions in detail, including timing frameworks applicable across mid-Atlantic conditions like Delaware’s.

Best Crops for Delaware Gardens

Delaware’s combination of long frost-free seasons, ample summer heat, and moderate humidity creates strong conditions for most common vegetables. The crops below represent the best performers based on University of Delaware Extension research [2] and consistent home garden results across the state’s growing regions.

Cool-Season Crops: Delaware’s Productive Spring and Fall Windows

Delaware’s dual cool-season windows — spring (February/March through May) and fall (August through November) — are among the most productive aspects of gardening in the state. Unlike states with harsh winters or brutally short cool seasons, Delaware provides enough moderate-temperature weeks to run full successions of lettuce, peas, brassicas, root vegetables, and leafy greens twice annually, with quality that rivals anything grown in more northerly regions.

The underlying reason these windows work so well is temperature. Lettuce produces its most tender, mildest leaves between 45°F and 65°F; spinach sweetens noticeably as temperatures approach freezing; peas set their most abundant crops when daytime highs stay in the 55°F–70°F range. Delaware’s spring delivers 6–10 weeks of these ideal conditions before June heat and humidity arrive. The fall window — often the season’s more productive of the two — stretches from late August through October or even into November in southern zones, with the additional benefit of dropping pest pressure compared to summer.

Peas: Delaware’s first direct-sow candidate of the season. In Sussex County, peas can go in as early as late February; in New Castle County, mid-March is a practical target. Peas tolerate light frost well — established plants handle temperatures in the upper 20s°F without significant damage — which makes them ideal for getting something growing before the last frost date arrives. Sow a second succession 3–4 weeks after the first for extended harvests before heat ends the season.

Spinach and lettuce: Both can be started under minimal protection (row cover or a cold frame) weeks before last frost. In northern Delaware, expect to sow spinach outdoors from mid-March; in the south, February cold-frame plantings are productive. The key to fall success with lettuce and spinach is counting backward from your expected first fall frost: sow spinach 45–60 days before that date to ensure harvest before hard freezes arrive.

Brassicas (broccoli, cauliflower, cabbage, kale): Spring brassicas need transplanting 4–6 weeks before last frost, which means starting indoors in late January (south) through mid-February (north). Fall is often better for broccoli and cauliflower in Delaware because decreasing temperatures through September and October trigger superior head development — dense, compact florets with less tendency to button or blow open prematurely. Start fall brassicas indoors in late June or early July for a late August transplant.

Root vegetables: Carrots, beets, and radishes go into the ground 3–5 weeks before last frost in Delaware. The coastal plain’s sandy loam soils across central and southern Delaware are particularly suited to carrots — the loose, well-drained texture allows roots to develop straight and long without forking or stunting that occurs in compacted or clay-heavy soils. Annual compost additions improve moisture retention in these sandy soils and reduce the watering burden during dry spells.

Extending the fall window: Lightweight row cover (1–1.5 oz/sq yd) adds 4–6°F of frost protection and meaningfully extends the fall harvest in all Delaware zones. A bed of kale or spinach under row cover in northern Delaware routinely produces through mid-November. In Sussex County, row-covered greens often persist into December. Cold frames push the window further still; in Lewes and Rehoboth Beach, cold-frame spinach can be harvested through January in mild winters.

Warm-Season Crops: Managing Delaware’s Hot, Humid Summers

Delaware summers are warm to hot, humid, and long — excellent growing conditions for tomatoes, peppers, cucumbers, squash, sweet corn, and sweet potatoes, provided gardeners actively manage the humidity-related challenges that come with the territory. Typical Delaware summers bring daytime highs in the 85°F–90°F range with relative humidity frequently above 70%, which is excellent for plant growth but also creates prime conditions for fungal diseases and pest pressure that require attention through July and August.

Tomatoes: Delaware’s long warm season supports both determinate and indeterminate varieties. The main challenge is blossom drop during peak summer heat: tomatoes fail to set fruit reliably when daytime temperatures exceed 90°F or nighttime temperatures stay above 75°F. This is a regular July and August issue across Delaware. Choosing heat-tolerant varieties (Heatmaster, Celebrity, Solar Fire) and ensuring consistent moisture through mulching and drip irrigation reduces the impact. A 2–3 inch layer of straw or wood chip mulch around tomato plants keeps soil temperatures moderated and dramatically reduces water stress during peak summer heat — the single most effective low-effort step Delaware tomato growers can take.

Peppers: Delaware’s hot summers suit peppers particularly well, especially in central and southern zones. Peppers prefer heat that tomatoes occasionally find excessive; they set fruit reliably through Delaware’s summer if moisture is consistent. Start peppers indoors 8–10 weeks before last frost — they need extra indoor time compared to tomatoes to reach transplant size — and choose disease-resistant varieties to reduce summer Phytophthora and bacterial spot problems.

Sweet corn: A traditional Delaware agricultural crop and well-suited to home gardens across the state. Full-season varieties (85–90 days) are viable in all Delaware zones given the long frost-free period; short-season varieties (75–80 days) allow double-succession planting in southern Delaware, where the first planting matures in late July and a second sowing produces in September. Block-plant corn in at least four rows for reliable pollination — single-row plantings produce poorly filled ears regardless of variety.

Disease and pest management: Delaware’s combination of heat and humidity creates conditions for several recurring problems. Powdery mildew appears on squash, cucumbers, and pumpkins by midsummer in most years; choose resistant varieties when available and maintain good air circulation through plant spacing and timely pruning of crowded growth. Early blight on tomatoes is nearly universal by August; applying copper-based fungicide preventively before first symptoms appear, and removing lower leaves as they yellow and age, manages rather than eliminates the problem. Japanese beetles peak in July and can rapidly defoliate beans, roses, and grape vines; hand-picking in early morning when beetles are sluggish is effective for small-scale plantings.

Thoughtful companion planting reduces pest pressure and improves pollination across warm-season crops. The companion planting guide covers which vegetables and flowers actively support each other — including pairings that attract beneficial insects and natural pest predators particularly relevant for managing Delaware’s summer garden challenges.

Flowers and Perennials for Delaware Landscapes

Delaware’s climate supports a genuinely diverse perennial palette. Most classic American garden perennials are reliably hardy across all Delaware zones, and the warmer southern region opens up marginally tender plants that struggle in harder-winter states to the north. The practical guiding principle for Delaware perennial selection is less about cold hardiness — Zones 6b–7b handle the vast majority of commonly grown perennials — and more about humidity tolerance and drought resilience during hot summers.

Reliably hardy perennials across all Delaware zones:

• Black-eyed Susan (Rudbeckia): Zones 3–9; thrives in Delaware’s summer heat; naturalizes readily in naturalistic plantings; outstanding fall color and winter seed heads for birds. Native to the mid-Atlantic region.
• Coneflowers (Echinacea): Zones 3–9; drought-tolerant once established; excellent pollinator plant; tolerates Delaware’s humid summers without significant disease problems.
• Daylilies (Hemerocallis): Zones 3–9; unfazed by Delaware winters and humid summers alike; extended-bloom and reblooming varieties stretch the flowering season from June through September.
• Peonies: Zones 3–8; thrive in Delaware’s cold-enough winters, which provide the chilling hours needed for reliable spring flowering; spectacular bloom; essentially permanent once established.
• Bee balm (Monarda): Zones 4–9; hummingbird and pollinator magnet; mildew resistance varies by variety — choose resistant types (Jacob Cline, Raspberry Wine) for Delaware’s humid summers.
• Ornamental grasses: Karl Foerster feather reed grass and Little Bluestem (a mid-Atlantic native) both perform exceptionally in Delaware, providing four-season interest with minimal maintenance in the state’s well-drained sandy soils.

Plants that push their limits in southern Delaware (Zone 7b): Gardeners in Sussex County and the coastal zone can trial plants that struggle in northern Delaware winters. Crape myrtle reliably reaches shrub-to-small-tree size in Zone 7b; in Zone 6b it dies back to roots in hard winters but resprouts. Rosemary survives in protected south-facing positions near the coast. Figs produce fruit as small trees in Zone 7b and survive as root-hardy shrubs in Zone 6b when planted against a south-facing masonry wall.

Native plants for Delaware landscapes: Delaware’s Coastal Plain and piedmont support a distinctive native plant palette that provides excellent wildlife value with minimal maintenance. Native azalea (Rhododendron viscosum), swamp rose (Rosa palustris), beautyberry (Callicarpa americana), and inkberry holly (Ilex glabra) are all native to Delaware and outperform non-native alternatives in supporting local pollinators, birds, and native bees. The Delaware Native Plant Society [2] maintains regional planting recommendations for home gardeners looking to expand native plantings.

Delaware Soil: Coastal Plain and Piedmont Conditions

Delaware’s soils divide roughly between the northern piedmont and the coastal plain that dominates the rest of the state. The two soil types have meaningfully different characteristics that affect drainage, spring warm-up timing, water retention, and how you amend for best results.

Northern piedmont soils (New Castle County uplands): The northern quarter of Delaware sits on the piedmont physiographic province. Soils here are heavier — typically silt loams and clay loams derived from metamorphic and igneous bedrock. They tend toward moderate drainage, higher native fertility, and slightly more organic matter than coastal plain soils. The trade-off is that they compact more easily under wet conditions and can be slow to dry and warm in spring, sometimes delaying planting by a week or more compared to sandier soils to the south.

Coastal plain soils (central and southern Delaware): The vast majority of Delaware sits on the Atlantic Coastal Plain, where soils are primarily sandy loam to loamy sand — the Downer, Sassafras, and Woodstown soil series dominate much of central and Sussex County. These soils drain quickly, warm up fast in spring, and rarely stay too wet to work. Their main limitation is low water-holding capacity and relatively low organic matter in their natural state. Annual compost additions of 2–3 inches worked into the top 8–10 inches consistently improve moisture retention and nutrient supply — the single most important amendment practice for coastal plain vegetable gardens.

Lowland and wetland-influenced soils: Delaware’s flat topography includes significant low-lying areas, particularly in Sussex County near tidal creeks and wetlands. These soils can be poorly drained and occasionally flooded in spring. Gardens in these positions benefit from raised beds, which solve the drainage issue while also warming faster in spring and providing better root zone conditions through the season.

pH and testing: Delaware’s coastal plain soils tend toward slightly acidic pH (5.5–6.5), which is appropriate for most vegetables and flowers. Sandy soils leach nutrients faster than piedmont soils and generally benefit from split-application fertilization rather than a single large dose early in the season. University of Delaware Cooperative Extension [1] offers soil testing services and provides Delaware-specific amendment recommendations — a soil test before your first season in a new garden is one of the highest-return investments available to any Delaware gardener.

Frequently Asked Questions

What USDA zone is Delaware?
Delaware spans USDA Hardiness Zones 6a through 7b. Wilmington and northern Delaware fall in Zone 6a–6b; Dover and central Delaware in Zone 7a; and coastal and southern Sussex County in Zone 7a–7b. The warmer zones in southern Delaware reflect Atlantic Ocean moderation of winter temperatures.

When should I plant tomatoes in Delaware?
In northern Delaware (Wilmington area), transplant tomatoes after May 1–10, when nighttime temperatures are reliably above 50°F. In Dover and central Delaware, May 1–5 is a reasonable target. In southern and coastal Delaware, April 15–20 is workable for hardened transplants. Start seeds indoors 6–8 weeks before your planting date — late February in the south, early March in the north.

Can I grow sweet potatoes in Delaware?
Yes — Delaware’s long warm season makes sweet potatoes a reliable crop, especially in central and southern zones. Plant slips after the last frost date when soil temperatures reach 65°F; sweet potatoes need 100–120 days to mature, which fits comfortably within Delaware’s 200–232 frost-free days. Northern Delaware growers can succeed with an early start (May 15–20) and black plastic mulch to warm the soil.

What are the biggest gardening challenges in Delaware?
Summer heat and humidity are Delaware’s primary challenges. Fungal diseases (powdery mildew, early blight, downy mildew) are common mid-season problems; choosing resistant varieties and maintaining good air circulation reduces their impact. Japanese beetles peak in July and can be severe on beans, roses, and fruiting plants. Drought stress is also common on the coastal plain’s sandy soils in July and August — consistent mulching and drip irrigation address both heat stress and drought simultaneously.

When does gardening start in Delaware?
For cold-hardy crops, Delaware gardening effectively starts in late February (southern zones) to mid-March (northern zones). Peas, spinach, radishes, and cold-hardy greens can go directly into the ground at those times. Warm-season crops — tomatoes, peppers, cucumbers — wait until after last frost, typically April 1–15 in the south and May 1–10 in the north. The first seed-starting activity for warm-season crops happens indoors from late January onward.

Is Delaware good for fruit trees?
Delaware has good conditions for most common temperate fruit trees. Apples, pears, and peaches all perform well, though the humid climate requires active disease management — fire blight on apples and pears and brown rot on peaches are recurring issues. Blueberries thrive if soil is adequately acidified (pH 4.5–5.5); Delaware’s coastal plain soils often need sulfur amendments to reach this range but respond well to treatment. Figs grow as small trees in Zone 7b southern Delaware and survive as root-hardy shrubs in Zone 6b northern Delaware.

What’s the best vegetable to grow in Delaware for beginners?
Green beans, zucchini, and tomatoes are all beginner-friendly crops that perform reliably across Delaware’s climate. Green beans are the easiest: direct-sow after last frost, water regularly, and harvest in 55–65 days. Zucchini is nearly foolproof but prolific — two plants are usually sufficient for a household. Tomatoes require more attention (staking, pruning, disease monitoring) but reward that effort with one of Delaware’s most productive summer crops.

Sources

[1] University of Delaware Cooperative Extension — gardening resources, soil testing, and regional planting guides

[2] University of Delaware Extension — Plant and Soil Sciences Home Horticulture Program