For cranberries, the timing of growth stage progressions through the season is dependent on both the variety and environmental cues such as day length, or temperature. The Cranberry growing degree day model uses heat units and time as a method to estimate plant phenological stages through the growing season. Researchers at University of Wisconsin -Madison and the USDA have developed a model which can be used to relate the amount of growing degree day unit accumulation to rough percentages of plants at different crop growth stages. This can be helpful as a crop management tool, or to predict harvest timing.

Calculating Growing Degree Days

For this model, a lower temperature threshold of 41F and an upper threshold of 85F is used to calculate growing degree day accumulation beginning on March 1st, or the start of the growing season. Growing degree days can be calculated from daily high and low temperatures, using a sine model, or via the Pest Prophet app, which uses hourly temperature data for a given field. These growing degree day calculations can be used to give an estimate of crop growth stage.

Estimating Crop Growth (Phenological) Plant Stage

Using the ‘Stevens’ cranberry variety, the following curves were derived for each crop growth (phenological) plant stage based on growing degree days:

For an in-depth description of different cranberry crop growth stages with photos, refer to this guide from University of Wisconsin-Madison.

As a general guideline, buds will begin to swell around 250 GDD (F) with about 50% of plants reaching the “cabbagehead” stage, when bud scales being opening and start to lose their red color, at 500 GDD (F).

Tthe “roughneck” stage, where the buds begin to elongate, occurs between 500 and 1,300 GDD (F) with the majorirty of plants reaching this stage between 700 and 800 GDD (F).

The “hook” stage, when flower pedicels lengthen and begin to droop, occurs between 750 and 1,700 GDD (F) peaking around 1,200 GDD (F).

After this, the majority of plants will have flowers open and bloom between 900 and 1,950 GDD (F), peaking around 1,500 GDD (F).

Finally, fruit-set will first begin at 1450 GDD (F), with the majority of plants reaching this stage at 1,700 GDD (F) and 100% by 2,000 GDD(F)

These estimates can be used a rough guideline for predicting cranberry crop growth in a given field.

Sources:

Chasen, Elissa and Steffan, Shawn. “Linking Growing Degree Days and Cranberry Plant Phenology”. Cranberry Crop Management Journal. University of Wisconsin- Extension. Volume XXX. Issue III. May 22, 2017.

https://counties.uwex.edu/wood/files/2012/09/05.22.2017_CCMJ.pdf