Au Rosa Plum

AU Rosa was released by the Alabama Agricultural Experiment Station at Auburn University as part of Joe Norton’s plum breeding program, which began in 1955 and produced multiple cultivars adapted to the humid Southeast. AU Rosa’s parentage is documented in Auburn’s own literature: a cross of Santa Rosa (the benchmark California Japanese plum, also a Luther Burbank introduction) and Starcher No. 1, a selection of Prunus angustifolia, the native Chickasaw plum. The Chickasaw parent contributes the heat and drought tolerance that straight Japanese plums lack in Southern summers, as well as meaningful resistance to the bacterial and fungal diseases that limit plum culture in humid climates. The resulting hybrid retains the firm, sweet flesh and heavy cropping associated with Japanese types while performing reliably in zones where Santa Rosa and comparable pure-salicina cultivars cannot. AU Rosa is among the Auburn series most widely distributed outside Alabama, valued across the Deep South and mid-Atlantic states.

Chill requirements of 700 to 750 hours place Au Rosa comfortably in zones 6 through 8, covering most of the mid-South and lower Mid-Atlantic. In humid climates, soil drainage matters more than in drier regions: standing water around the root crown favors Phytophthora and Pseudomonas infections, so raised beds or sloped planting sites are worth the extra preparation. A soil pH of 5.5 to 6.5 keeps phosphorus and micronutrients available; lime or sulfur adjustments should be made several months before planting based on a soil test. Moderate consistent moisture during fruit set—roughly late April through June in a temperate climate—directly affects fruit sizing and prevents the premature drop that undercuts yield. Avoid overhead irrigation, which wets the canopy and prolongs leaf wetness periods that favor fungal disease. Once established, the tree tolerates brief dry spells but will set smaller fruit and may drop early under prolonged drought. Plant spacing of 12 to 15 feet allows adequate airflow and room for the vase-shaped canopy to develop without crowding.

USDA Hardiness Zone: 5-8
AHS Heat Zone: 5-9
Chill Hours: 750-950
Sun Requirements: Full Sun
Soil pH: 5.5-6.5
Soil Type: Well-drained loam; adapts to sandy loam or clay loam
Soil Drainage: Well-drained
Water Requirements: Medium; consistent moisture during establishment and fruiting
Drought Tolerance: Low to Moderate
Plant Spacing: 12-15 ft apart
How to Prune: Prune in late winter to open vase shape; remove crossing branches; thin annually to maintain 8-10 ft spread

Au Rosa grows with a naturally upright, vase-shaped habit, reaching 12 to 18 feet tall and spreading 12 to 15 feet wide at maturity. The vase form—where scaffold limbs angle outward from a central trunk—is well suited to annual thinning cuts that open the canopy to light and air. Fast growth of one to two feet per year means the tree reaches bearing size in two to four years, but training cuts in the first three to four years are critical to establishing strong branch angles. Leaders with narrow crotch angles are prone to splitting under a heavy crop load; select scaffolds with angles of 45 to 60 degrees during early training. Dark green foliage turns red to yellow in fall. The species lacks thorns, which simplifies harvest and pruning work. Root architecture is moderately shallow and wide-spreading, so competing grass and weeds at the drip line reduce water uptake and slow establishment; a maintained mulch ring extending to the canopy edge pays dividends in the first few years.

Mature Height: 12-18 ft tall
Mature Spread: 12-15 ft wide
Growth Habit: Upright, vase-shaped
Growth Rate: Fast; 1-2 feet per year
Foliage Type: Deciduous
Food Forest Layer: Canopy, Sub-canopy
Leaf Color: Dark green
Fall Foliage Color: Red to yellow
Thorns?: No
Attracts Wildlife: Bees, butterflies, birds
Life Span: 20-40 years

Au Rosa Plum flowers in the mid relative window in the Zone 7 Ozarks planning model. Auburn and Rutgers say self-fruitful; UGA says not self-fruitful. Recommend a compatible overlapping cultivar despite likely partial/self fertility.

Bloom Season: Mid
Bloom Window: Early - Mid Apr
Pollination Requirements: Auburn and Rutgers say self-fruitful; UGA says not self-fruitful. Recommend a compatible overlapping cultivar despite likely partial/self fertility.
Pollination Mechanism: Insect (bee)
Flower Color: White

Diameter reaches 1.5 to 2 inches—medium-sized by Japanese plum standards—with deep red to reddish-purple skin and golden-yellow flesh underneath. The contrast between the dark skin and bright interior makes it visually distinctive at market. Flavor runs sweet and juicy with moderate acidity; the flesh is firm enough to hold up in cooking and canning rather than turning soft. Harvest falls in mid-June through early July in temperate climates, ahead of most Japanese plum cultivars. At maturity, yields reach 50 to 100 pounds per tree—heavy and consistent—with fruit ripening in overlapping flushes over two to three weeks rather than all at once, which spreads the harvest workload. Storage life of two to four weeks refrigerated makes it viable for small commercial sales or home preservation. Culinary applications include fresh eating, preserves, jam, and baking. As with all stone fruits, the pits, leaves, and bark contain cyanogenic glycosides and should not be consumed.

Ripening Season: Early
Harvest Window: Mid Jun - Early Jul
Fruit Size: 1.5-2 inch
Flavor: Sweet, juicy; golden-yellow flesh
Fruit Color: Deep red to reddish-purple skin; golden-yellow flesh
Fruit Texture: Firm and juicy
Bearing Habit: Annual bearer; heavy and consistent yields
Years to Bear: 2-4 years
Yield: 50-100
Storage Life: 2-4 weeks refrigerated
Culinary Uses: Fresh eating, preserves, jam, baking, canning

The AU series breeding program’s primary goal was disease resistance, and Au Rosa delivers across every major plum pathogen tracked in Eastern humid regions. Brown rot (Monilinia fructicola) shows strong inherent resistance in Au Rosa—growers in humid climates report far fewer losses at harvest than with conventional Japanese varieties. Black knot (Dibotryon morbosum) and bacterial spot (Xanthomonas arboricola pv. pruni) are likewise resistant, reducing the pressure for protective spray programs. Plum leaf scald (Xylella fastidiosa), spread by sharpshooter leafhoppers, shows near-immunity in Au Rosa—a commercially significant trait for Gulf Coast and lower mid-Atlantic growers. Bacterial canker (Pseudomonas syringae pv. syringae) resistance further reduces the risk of structural limb damage in cold-wet spring conditions. Pest management requires more active attention. Plum curculio (Conotrachelus nenuphar), Oriental fruit moth (Grapholita molesta), peach tree borer (Synanthedon exitiosa), and spotted wing Drosophila (Drosophila suzukii) all attack with moderate effectiveness. Jar limbs over a tarp at dusk below 60°F to dislodge curculio before egg-laying; kaolin clay from petal fall through early fruit sizing reduces oviposition. Peach tree borer is managed by keeping trunk bark dry and applying beneficial nematodes (Steinernema carpocapsae) around the base in late summer. SWD monitoring with apple cider vinegar traps during late June lets growers time harvests before infestation peaks.

Brown Rot: Resistant
Black Knot: Resistant
Bacterial Spot: Resistant
Plum Leaf Scald: Very Resistant
Bacterial Canker: Resistant
Plum Curculio: Moderately Susceptible
Oriental Fruit Moth: Moderately Susceptible
Peach Tree Borer: Moderately Susceptible
Spotted Wing Drosophila: Moderately Susceptible

• Frost protection at bloom: Au Rosa flowers early in temperate climates — keep overhead frost cloth handy for predicted hard frosts after bloom begins, as a single freeze event can eliminate the season's crop.
• Curculio window management: Plum curculio egg-laying concentrates in the first three to four weeks after petal fall; apply kaolin clay immediately after bloom drops and reapply after rain to maintain protection during this critical window.
• Thin for fruit sizing: Heavy annual bearing means the tree can overbear; hand-thin to one fruit every three to four inches in late May to push remaining fruit to full size and prevent limb breakage.
• Vase pruning discipline: Prune in late winter before bud break to maintain an open vase shape; heading cuts removing 20–25% of last year's growth keep fruit wood close to the scaffold and reduce interior shading.
• SWD harvest timing: Begin checking fruit for spotted wing drosophila infestation as skin color deepens; refrigerate promptly at harvest to slow larval development and extend shelf life.

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