Table 1.

Predicted number of heat units required to reach a given budbreak percentage on the terminal 30 cm (12 in.) of stems of selected red maple cultivars, 1999-2000.

CultivarHours chilledInitial budbreak10% budbreak25% budbreak
Predicted number of heat unitsz
‘Autumn Fantasy’2001,716y2,0852,487
4001,2451,6152,017
6008431,2121,614
8005098781,280
1,0002436121,015
1,20046415817
r2 = 0.63
October Glory®200178418501948
4001,3481,4141,513
6009701,0351,134
800648713812
1,00038244847
1,200174240338
r2 = 0.50
‘Franksred’ (Red Sunset®)2001,7282,0522,419
4001,2071,5311,899
6007821,1061,474
8004537771,144
1,000219543910
1,20080404771
r2 = 0.66
  • z Calculated with PROC REG, using the SAS stepwise procedure to determine the best model.

  • y One heat unit equals one hour in greenhouse at a temperature of at least 22°C (72°F).