Tree Fruit Newsletter — April 26, 2024

Highmoor Farm Bud Stages

McIntosh apple trees are at half-inch green as of April 25, and Honeycrisp is at green tip. Pears are at half-inch green, and peaches are at the red calyx stage.  The cold temperatures have us all worried about freeze damage, so I am resending the hardiness numbers for each bud stage.   The current cold spell will also slow down bud development and delay the date of full bloom.

Table 1. Estimated range of temperatures (°F) to cause 10% or 90% flower loss.

1/2 inch Green Tight Cluster Early Pink Pink King Bloom Full Bloom
10% 23 27 24 28 25 25
90% 15 21 28 25 28 28
For Red Delicious, measured in Washington.


Table 2 may be more accurate for conditions in Maine since we have not had much warm weather lately.

Table 2. Estimated range of temperatures (°F) to cause apple 50% flower loss.

Early Pink Late Pink King Bloom Full Bloom
Lower limit 21.7 22.5 23.7 24.4
Upper Limit 25.0 25.9 26.6 27.7
From Szalay et al. 2019, based on six years of research in several varieties grown in Hungary. The lethal temperature varied from year to year and among ten varieties.

Table 3. Estimated range of temperatures (°F) to cause peach 50% flower loss.

Red calyx Pink First Bloom Full Bloom
10% 27 27 27 28
90% 17 20 22 27
Colorado State Univ.


Renae Moran
University of Maine Cooperative Extension
PO Box 179
Monmouth, ME 04259
(207) 933-2100

In complying with the letter and spirit of applicable laws and pursuing its own goals of diversity, the University of Maine System does not discriminate on the grounds of race, color, religion, sex, sexual orientation, transgender status, gender, gender identity or expression, ethnicity, national origin, citizenship status, familial status, ancestry, age, disability physical or mental, genetic information, or veterans or military status in employment, education, and all other programs and activities. The University provides reasonable accommodations to qualified individuals with disabilities upon request. The following person has been designated to handle inquiries regarding non-discrimination policies: Director of Equal Opportunity, 5713 Chadbourne Hall, Room 412, University of Maine, Orono, ME 04469-5713, 207.581.1226, TTY 711 (Maine Relay System).