Sweetheart Blueberry

Sweetheart was developed by Mark K. Ehlenfeldt at USDA-ARS’s Chatsworth, New Jersey research station. The cross was made in 1996, combining TH 275 — a University of Georgia southern highbush selection carrying approximately 15 percent Vaccinium darrowii ancestry — with G 567, a northern highbush selection, to produce a cultivar with southern heat tolerance layered onto a cold-hardy northern framework. Ehlenfeldt selected the variety in 1999 and continued evaluating it through 2009 before formally releasing it in June 2010. USDA-ARS released Sweetheart unconditionally — no patent, no royalty, no licensing restriction — making it freely available to all growers. The breeding objective centered on post-harvest flavor retention and firm texture: field trials recorded average yields of 15 pounds per plant versus 12.1 pounds for Duke, with medium to medium-large fruit that maintains aromatic quality for several days under refrigeration. In mild autumns the plant can produce a modest secondary flush on current-season wood.

Sweetheart performs best in full sun with consistently moist, well-drained, highly acidic soil. Maintaining pH in the 4.5-5.0 range is non-negotiable — blueberries grown outside that window show iron chlorosis, stunted growth, and sharply reduced yields. Test soil before planting and amend with elemental sulfur months ahead of establishment; retest annually. A 3-4 inch layer of acidic wood-chip or pine-bark mulch conserves moisture, moderates soil temperature, and feeds the ericoid mycorrhizal community that highbush blueberries depend on. Sweetheart's 700-800 chill hour requirement is well matched to USDA zones 4–8, where it opens its primary crop in late May to early June. Growth rate is slow to moderate; expect 3-4 years before full production. Space plants 3-5 feet apart in rows; prune dead wood and crossing canes in late winter to keep fruiting wood young and productive. Container culture is viable in large pots — 15-25 gallon minimum — with an all-peat or peat-perlite medium kept at correct pH.

USDA Hardiness Zone: 4-8
AHS Heat Zone: 4-7
Chill Hours: 750-950
Sun Requirements: Full Sun
Soil pH: 4.5-5.0
Soil Type: Acidic, sandy loam high in organic matter
Soil Drainage: Well-drained (excellent drainage required; intolerant of waterlogging)
Water Requirements: Medium (consistent, even moisture; shallow-rooted and intolerant of both drought and waterlogging)
Drought Tolerance: Moderate
Plant Spacing: 3-5 ft apart
Container Suitability: Yes (suitable for large containers)

Sweetheart reaches 5-6 feet tall and 3 feet wide at maturity, forming a moderately compact, upright Northern Highbush shrub. The deciduous foliage emerges with a bronze-green flush in spring, transitions to deep green through summer, and often develops orange-red autumn color before leaf drop — providing ornamental value beyond the harvest season. Growth rate is slow to moderate, typical of the highbush group. Salt tolerance is low; avoid sites with road salt runoff or brackish irrigation. Wind tolerance is moderate — exposed hillside plantings may benefit from a windbreak to reduce late-frost injury to blossoms. Wildlife engagement is strong: bees and native pollinators work the bell-shaped white flowers in spring, songbirds and small mammals compete for fruit near season-end. Deer readily browse the tender twigs and shoots, so protective fencing is advisable in high-pressure landscapes. Sweetheart carries no fragrance in fruit or flower, and is listed as Native to North America within its Vaccinium corymbosum lineage.

Mature Height: 5-6 ft tall
Mature Spread: 3 ft wide
Growth Habit: Upright, multi-stemmed deciduous shrub
Growth Rate: Slow to Moderate
Foliage Type: Deciduous
Food Forest Layer: Shrub
Permaculture Role: Edible fruit shrub; pollinator nectar source; wildlife food (berries) and habitat
Leaf Color: Green
Fall Foliage Color: Red-orange
Thorns?: No
Attracts Wildlife: Flowers attract bumblebees, native bees, and honey bees; ripe berries attract songbirds and small mammals
Life Span: 20-50 years

Sweetheart requires cross-pollination for full, consistent crops — self-pollinated sets are light and fruit size suffers. Plant at least one compatible partner variety within 50 feet. Bluecrop Blueberry and Bluegold Blueberry are the strongest on-website pairings: both are Northern Highbush cultivars that flower in the mid-April window overlapping Sweetheart's bloom. Honeybees are effective pollinators, but bumblebees (which buzz-pollinate and improve berry set on blueberry flowers) deliver noticeably better results — avoid broad-spectrum sprays during bloom. Space partner plants no more than 50 feet from Sweetheart in the same pH-managed bed; pollinators will shuttle between rows in that range.

Bloom Season: Early
Bloom Window: Mid Apr - Early May
Pollination Requirements: Partially self-fertile; a second cultivar improves yield
Pollination Mechanism: Insect-pollinated (buzz/sonication pollination by bumblebees and native bees; honey bees also forage)
Flower Color: White (bell-shaped)
Ploidy: Tetraploid (4x)

Sweetheart produces light-blue, very firm berries averaging 0.5 inch in diameter with a sweet, aromatic flavor profile that holds notably well after picking. Where most early-season highbush varieties peak at harvest and soften within a day or two, Sweetheart maintains its flavor and texture under refrigeration for several days — a genuine advantage for growers who sell at farmers markets or to small grocers. Ripe fruit concentrates in late May through early June in temperate climates, making Sweetheart one of the first Northern Highbush varieties to bear. In favorable mild autumns, a secondary light crop may appear on current-year canes. Mature plants yield around 15 pounds annually. The firm texture holds well in muffins, cobblers, and pies without turning to mush during baking, and the aromatic sweetness is compelling eaten fresh out of hand. Fruit is suitable for fresh sales, freezing, and culinary processing.

Ripening Season: Very Early
Harvest Window: Late May - Early Jun | Late Aug - Early Sep
Fruit Size: 0.5 inch
Fruit Weight: 1.6 g average
Flavor: Sweet, aromatic; superior flavor retained in storage
Fruit Color: Light blue
Fruit Texture: Very firm
Bearing Habit: Double-cropping (primary early-season crop on prior-year wood; occasional light secondary crop on current-year growth in mild autumns)
Years to Bear: 2-3 years
Yield: 15 per bush at maturity
Storage Life: 2-3 weeks refrigerated; superior flavor stability in storage
Culinary Uses: Fresh eating, baking, freezing, preserves, jams, smoothies, pies, muffins

Sweetheart carries the standard disease and pest exposure profile of Northern Highbush blueberries grown in humid climates. Mummy berry (Monilinia vaccinii-corymbosi) is the most consequential fungal threat: raking and destroying mummified fruit and leaf litter before bud break breaks the spore cycle without chemical inputs. Botryosphaeria stem blight (Botryosphaeria dothidea) enters through wounds and dead wood — prompt removal of blighted canes well below the margin, with tool sanitation between cuts, limits spread. Anthracnose fruit rot (Colletotrichum acutatum) pressure rises with wet weather at harvest; good air circulation through annual pruning is the primary cultural control. Phytophthora root rot (Phytophthora cinnamomi) is avoided almost entirely by never planting in standing water and maintaining a raised or mounded bed. Septoria leaf spot (Septoria albopunctata) causes cosmetic defoliation but rarely threatens production when plants are well-nourished. On the pest side, Spotted Wing Drosophila (Drosophila suzukii) is the most urgent early-season concern; fine-mesh exclusion netting deployed at fruit color change is the most reliable organic control. Blueberry maggot (Rhagoletis mendax), cranberry fruitworm (Acrobasis vaccinii), and plum curculio (Conotrachelus nenuphar) are managed through sanitation, exclusion, and kaolin clay applications where warranted.

Mummy Berry: Moderately Susceptible
Botryosphaeria Stem Blight: Moderately Susceptible
Anthracnose Fruit Rot: Moderately Resistant
Phytophthora Root Rot: Moderately Susceptible
Septoria Leaf Spot: Moderately Resistant
Spotted Wing Drosophila: Moderately Susceptible
Blueberry Maggot: Moderately Susceptible
Cranberry Fruitworm: Moderately Susceptible
Plum Curculio: Moderately Susceptible

• Test and amend soil pH early: Amend with elemental sulfur 6–12 months ahead of planting and retest each spring — pH drift above 5.0 is the leading cause of production failure.
• Plant pollinators within 50 feet: Pair with Duke or Jersey for bloom overlap and berry-size improvement; keep partners in the same pH-managed bed.
• Deploy SWD netting at first color change: Install exclusion netting when fruit first shows color, not at full ripeness — the window for effective protection closes faster than most growers expect.
• Mulch deeply each year: Apply 3–4 inches of pine bark or wood chips and refresh annually to maintain soil moisture and suppress weeds without cultivation.

Our 365-Day Plant Guarantee: We ensure that our plants are delivered to you alive and healthy. If your plant does not survive its first year, you're eligible for store credit under these conditions:

1. Your location falls within the appropriate USDA hardiness zone for the plant variety (refer to our hardiness zone map).
2. You maintain the roots' moisture and plant within three days of delivery, following the instructions in our Planting Guide.

If you're concerned about your plant's health, please consult our guide, How to Tell if Your Tree is Dead or Dormant. Remember, our plants are shipped in a dormant state and may leaf out at different times based on their species. To check for plant vital