A few notes that may add to what’s been shared:
Terminology: “Cold stratification” applies to seed; for established plants you’re manipulating endodormancy via accumulated chilling and subsequent heat. S. prunifolia sets flower buds late summer on current-season wood and needs a substantive chill period to release those buds.
Forcing/out‑of‑season bloom (best with containerized stock):
- Allow natural bud initiation (late summer); cease high N by mid‑July to favor spur formation.
- Provide 6-10 weeks at 1-5°C in darkness/moist media, then force at 16-18°C days, 12-14 h light, keeping nights 8-10°C for the first 10-14 days. Mist lightly to limit desiccation. You’ll get usable bloom 3-5 weeks after transfer, but this is unreliable outdoors because insufficient chilling or heat spikes disrupt synchrony.
- Cut‑branch forcing works well: harvest after adequate chill, recut under water, hold at 18°C with high RH; flowers open in 10-18 days.
Pruning for compact, floriferous habit:
- Renewal approach only right after bloom: remove 20-30% of the oldest canes at the crown each year; head remaining flowering laterals back to 2-4 buds. Avoid summer/fall shearing, which strips next year’s flower buds.
- A hard rejuvenation (at ground) on a 3-4 year cycle followed by selective heading produces dense spur wood and heavier bloom in years 2-3.
Substrate and nutrition:
- Target pH 6.0-6.5; above 7.2 flower density commonly drops with interveinal chlorosis. If irrigation water is alkaline, acidify to keep root‑zone pH in range.
- Keep EC moderate; supply 60-90 mg·L⁻¹ N during active shoot growth, taper by mid‑July, and maintain K on the higher side relative to N to favor bud set.
Microclimate:
- Full sun is critical; east or southeast exposures yield denser spurs with less winter desiccation. South/west walls often force premature dehardening and spring bud kill after radiative frosts.
- Wind exposure correlates with reduced distal bud survival; windbreaks or leeward placement improves inflorescence continuity.
- Heat‑island sites can under‑chill; expect uneven bloom there.
Growth regulators (container/nursery use; check labels/local regs):
- Low‑rate paclobutrazol drenches give durable height control and increase spur density; daminozide can tighten internodes; ethephon after soft‑pinch improves basal branching. Trial small cohorts first-rates are cultivar- and media‑dependent.
Simple assessment protocol:
- Randomized blocks (≥10 plants/treatment). Record chill hours, GDD to 10% bloom, buds per 10 cm of previous‑year wood, mean internode length, cane diameter class distribution, and inflorescences per lateral. Score flower coverage on a 1-5 visual scale at peak and again two weeks later to capture persistence.
- Soil/solution pH and EC every 3-4 weeks; leaf tissue N, Fe, Mn mid‑summer if chlorosis appears.
Bottom line: true off‑season landscape bloom is impractical, but container forcing after controlled chilling is feasible. For landscapes, the biggest levers for flower density and compactness are disciplined post‑bloom renewal pruning, correct pH, moderated N, full sun with morning exposure, and avoiding under‑chilled or heat‑reflective sites.
