Ulster Sweet Cherry
Pollination & Compatibility Guide
Ulster cherry pollination guide: S-genotype (S3S4, Group III), compatible partners (Rainier, Van, Lapins), bloom overlap, and orchard management.
Ulster is Self-Incompatible (Needs 1 Partner)
Incompatible with Bing, Lambert, Napoleon/Royal Ann, Emperor Francis and Kristin. It is compatible with Rainier (Group IX). Ulster needs at least one compatible pollinizer from bloom group 2–4 to set a reliable crop.
- S-Genotype / Genetics
- S3S4 (Group III)
- Required Companions
- 1 Compatible Partner
- Bloom Group
- Group 3 (Mid-Spring)
- Harvest Timing
- Mid Season
Flowering Period & Overlap Window
Sweet and sour cherry flowering periods are classified into numbered bloom groups (1 through 5). Cross-pollination requires overlapping bloom timing between genetically compatible cultivars.
Any compatible cherry cultivar flowering within Group 2 to 4 provides matching blossom overlap.
Compatible Pollination Partners (17)
| Cultivar | Bloom Group | Overlap Type | Harvest | Primary Uses | Interactive Test |
|---|---|---|---|---|---|
| Group 3 | Adjacent Overlap | Mid | Fresh Eating | Test Cross | |
| Group 3 | Adjacent Overlap | Mid | Fresh Eating, Dessert | Test Cross | |
| Group 3 | Adjacent Overlap | Mid | Fresh Eating | Test Cross | |
SelahGuideUniversal Donor | Group 3 | Full Overlap | Mid | Fresh Eating | Test Cross |
StellaGuideUniversal Donor | Group 3 | Full Overlap | Mid | Fresh Eating, All-Purpose | Test Cross |
SunburstGuideUniversal Donor | Group 3 | Full Overlap | Mid | Fresh Eating | Test Cross |
| Group 3 | Adjacent Overlap | Mid | Fresh Eating, Canning | Test Cross | |
Attika | Group 4 | Adjacent Overlap | Late | Fresh Eating | Test Cross |
| Group 2 | Adjacent Overlap | Early | Fresh Eating | Test Cross | |
| Group 2 | Full Overlap | Early | Fresh Eating | Test Cross | |
| Group 2 | Adjacent Overlap | Early | Fresh Eating | Test Cross | |
| Group 2 | Full Overlap | Early-Mid | Fresh Eating | Test Cross | |
| Group 4 | Adjacent Overlap | Mid | Fresh Eating | Test Cross | |
LapinsGuideUniversal Donor | Group 4 | Full Overlap | Late | Fresh Eating, Canning | Test Cross |
SkeenaGuideUniversal Donor | Group 4 | Full Overlap | Late | Fresh Eating | Test Cross |
Incompatible Varieties & Exclusions (6)
These cherry varieties overlap in flowering time with Ulster but cannot fertilise it due to shared S-allele genetic incompatibility groups.
Bing shares both S-alleles with Ulster — they are mutually sterile, whatever their bloom overlap suggests.
Emperor Francis shares both S-alleles with Ulster — they are mutually sterile, whatever their bloom overlap suggests.
Kristin shares both S-alleles with Ulster — they are mutually sterile, whatever their bloom overlap suggests.
Utah Giant's S-genotype is not recorded. For this crop compatibility is computed from S-alleles, so it cannot be offered as a partner without one.
Vibrant's S-genotype is not recorded. For this crop compatibility is computed from S-alleles, so it cannot be offered as a partner without one.
Vindskörsbär (Victor)'s S-genotype is not recorded. For this crop compatibility is computed from S-alleles, so it cannot be offered as a partner without one.
Ulster Sweet Cherry Pollination & Orchard Management
Ulster is a high-quality dark sweet cherry developed at Cornell University's New York State Agricultural Experiment Station in Geneva. Bred from a cross between Schmidt and Lambert, Ulster produces exceptionally large, firm, dark mahogany fruit with rich dessert sweetness and balanced acidity, making it a standout selection for direct retail farm markets and commercial orchard blocks across the northeast.
Genotypically, Ulster belongs to Incompatibility Group III (S3S4). It is gametophytically self-incompatible and mutually sterile with Bing, Emperor Francis, and Kristin. Crucially, Ulster is completely compatible with Rainier (Group IX, S1S4), Schmidt (Group XIII, S2S4), and Van (Group II, S1S3), which provide dependable, high-viability pollen sources across overlapping blossom windows.
Ulster flowers reliably in mid-spring (Bloom Group 3). Planting Ulster with early-to-mid season pollinizers and self-fertile universal donors like Lapins (S1S4′), Skeena (S1S4′), or Sweetheart (S3S4′) ensures heavy commercial fruit set while providing valuable reciprocal cross-pollination for companion rows across the entire block.
Key Orchard Considerations for Ulster
Ulster was selected specifically for enhanced resistance to skin split and cracking compared to Bing, making it well suited to eastern North American growing conditions.
The tree forms abundant fruiting spurs along two-year-old wood. Prune to maintain sunlight penetration into the inner canopy to preserve spur viability and uniform fruit colouring.
Dark, firm fruit is highly attractive to Spotted Wing Drosophila (SWD) and cherry fruit fly as it colours; maintain tight monitoring traps starting at initial straw-yellow stage.
Take Ulster from Planning to Planting
Use Kropigo's free browser tools to model your block density, tree counts, and pollinizer rows, then maintain permanent orchard records row by row.
Pollination Checker
Check Ulster against supported cultivars with compatible flowering and pollination data.
Commercial Block Planner
Calculate high-density tree spacing, row geometry, and establishment costs.
Block Record Keeping
Track pruning, chemical thinning, and harvest tallies block by block from the orchard.