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April 11, 2016

April's cooler temps help protect fruit trees

ST. PAUL, Minn. (04/6/2016)— The good news about the recent weather’s cooler trend is that it is holding back the flowering buds of our fruit trees. Apple tree buds are presently in a stage that could withstand temperatures into the mid-teens; however, a dip into low teen or single digit temperatures would be problematic.

The extended April forecast looks good with the lowest overnight lows in the low 20s. Average low temperatures through April are also good, with lows in the high 20s to mid-30s. Continued cooler weather will hold buds back; the longer they are held back, the better the chances of avoiding a damaging late frost.
Man inspects fruit tree blossoms

Freeze damage depends on bud stage
Damage experienced from late spring frosts is a function of the temperature sensitivity of a bud, which in turn depends on its type and its stage of growth. For example: A tight strawberry bud can tolerate temperatures down to 22 degrees. As it opens, that critical temperature rises to 26 degrees. The fruit’s critical temperature is 28 degrees; the flower itself is the most sensitive, with a critical temperature of 30 degrees.

Deciduous fruit trees follow a similar pattern although the temperatures will not be exactly the same. The extent of frost damage depends on the low temperature reached and the time it spends at that temperature.

This chart from Michigan State University Extension shows critical temperatures for tree fruit bud development.

Know your microclimate
To some extent, frost protection is a phenomenon and depends on a plant's microclimate—its exact location and characteristics. This is determined by your exact location and topographical characteristics. Buildings may offer the plant some protection. Large bodies of water moderate air temperatures and urban areas with buildings and pavement act as heat syncs that can radiate heat back at night.


  • Topography: South-facing slopes with early spring warmth can encourage fruit trees to flower earlier and be more vulnerable to late spring frosts.
  • Air drainage: Fruit trees planted in an area where cold air collects can experience colder temperatures than plants on the upper part of slopes.

For more, visit the wide range of information on growing fruit from the University of Minnesota Extension.
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Source: Karl Foord, University of Minnesota Extension Educator, foord001@umn.edu, 651-480-7788

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