REFERENCE DATE 

Reference dates recorded are a statewide and varietal-wide average and should be calculated in your area to be more precise. Reference date is considered to be that date when 80 percent of the fruits sliced have hardened pits at the very tip plus 10 days.

Full bloom is considered to be that stage of bloom where a few petals have begun to fall. Some years the bloom is sharp and easy to define whereas in borderline chilling years the bloom can be rather straggly.

EFFECTS OF SOIL CONDITIONS IN FROST PROTECTION 

Soil conditions make a great deal of difference in frost protection. Heat is absorbed by the soil during the day and released to warm the blossoms at night and early in the morning. Maximum exposure of the soil to sunshine is necessary to provide optimum frost protection.

The following is a table of relative temperature differences as influenced by orchard floor conditions: 

Bare, firm, moist ground................................. warmest 
Shredded covercrop, moist ground..................1/2º F colder 
Low-growing covercrop..................................1º - 3º F colder 
Dry, firm ground...............................................2º F colder 
Freshly disked, fluffy ground.............................2º F colder 
High covercrop................................................2º - 4º F colder 
Where covercrop restricts air drainage..............6º - 8º F colder 

The following are temperatures that peaches may endure for 30 minutes or less without commercial damage (sheltered thermometers): 

Peaches . . . . . . . 
 

Buds Close But  
Showing Color 		 Full  
Bloom 		 Small, Green  
Fruits 
25ºF  28ºF 29ºF 
Sizes
Reported Every 5 Days from Reference Date
modesto
kingsburg
yuba city
Provided in pdf format Get viewer here
Last Updated: Monday, February 14, 2000

WINTER CHILLING
  To adequately satisfy the chilling requirement for cling peaches (break the dormancy), approximately 800-1,000 total hours under 45ºF are needed. Chilling quality varies. The highest quality chilling for cling peaches would be in December-January temperatures of 28-34ºF at night and a daytime temperature in the 30s-40s. Warm, sunny days in January or December can cancel out the benefits of optimum low temperature chilling. Such years with intermittent warm weather during the chilling period are indicated in the accompanying table.

YEAR CHILLING HOURS FULL BLOOM REFERENCE DATE FULL BLOOM TO R.D.
1981 1,061 3-9 5-27 79 days
1982 1,320 3-12 6-1 81 days
1983 1,475 3-7 6-2 87 days
1984 1,144 3-7 5-23 77 days
1985 1,322 3-11 5-20 70 days
1986 1,046 2-27** 5-15 77 days
1987 1,091 3-13 5-21 69 days
1988 1,329 3-1 5-11 71 days
1989 1,233 3-13 5-22 70 days
1990 1,544 3-18 5-21 64 days
1991 1,041 3-5 5-31 87 days
1992 974 3-7 5-18 72 days
1993 1,115 3-11 5-21 71 days
1994 1,050 3-10 5-19 70 days
1995 1,108 2-27** 5-24 86 days
1996 703* 3-14 5-19 66 days
1997 1,309 3-8 5-12 65 days
1998 1,586 3-14 5-26 73 days
1999 1,197 3-15 6-1 78 days
2000 769 3-14 5-17 64 days
2001 1,311 3-11 5-18 68 days
2002 801 3-10 5-20 71 days
2003 788 3-9 5-23 75 days
2004 825 3-9 5-11 63 days
2005 988 3-3 5-16 74 days
2006 807 3-14 5-27 74 days
2007 1,084 3-9 5-16 68 days