Understanding Runner Formation and Management in Strawberries

Wednesday, February 5, 2025

 Berry interesting take aways from the Nova Scotia Horticultural Congress 2025

Insights from Dr. Edward Durner’s Research at Rutgers University

Dr. Edward Durner of Rutgers University has extensively studied strawberry physiology, particularly the environmental and genetic factors influencing runner production. His research sheds light on the mechanisms controlling runner formation and provides practical management strategies to optimize strawberry cultivation.

Strawberries have a unique method of propagation, through runners, also known as stolons. These slender, above-ground stems extend from the mother plant, generating genetically identical daughter plants. While runners are essential for strawberry propagation, their formation can sometimes be excessive, diverting energy from fruit production. Understanding how to manage runners effectively can lead to better yields and healthier plants.

Runner formation originates in specific plant structures called axillary meristems, which are clusters of actively dividing cells located at the base of each leaf. These meristems have three potential developmental pathways:

Dormancy – The meristem remains inactive.

Runner Formation – The meristem develops into an elongated stolon that produces daughter plants.

Branch Crown Formation – Instead of producing a runner, the meristem develops into a branch crown, which can generate additional flower buds.

Understanding this process is crucial because strawberries must balance vegetative growth (runners and leaves) with reproductive growth (flower and fruit production).  This balance is influenced by environmental signals and genetic predisposition.

Several factors determine whether a strawberry plant will produce runners, flowers, or branch crowns:

Photoperiod (Day Length)

-Short-day cultivars (June-bearing varieties like Wendy, Lila.....etc. ) form flower buds when exposed to short daylight hours (less than 12 hours per day). However, under long days, they produce runners instead of flowers.

-Long-day cultivars (often called day-neutral strawberries, such as Albion and Seascape) require longer daylight periods (more than 12 hours per day) to initiate flowering. Under short-day conditions, they tend to produce more runners.

-This distinction is important for growers selecting cultivars based on their climate and production goals.

Temperature

-Optimal temperatures for runner formation typically range between 60°F and 80°F (15°C–27°C).

-When temperatures are too high, plants may enter a semi-dormant state, reducing runner formation.

-Cool temperatures (below 50°F/10°C) can suppress runner growth and encourage flowering in short-day cultivars.

Nitrogen Fertilization

-Excess nitrogen promotes vegetative growth, leading to excessive runner formation at the expense of fruit yield.

-Delaying nitrogen application until after flower buds have formed encourages fruit production rather than excessive vegetative growth.

-A trial with Chandler strawberries demonstrated a 27% yield increase when nitrogen was applied a week after detecting flower buds rather than at planting.  Detecting flower bud formation uses a technique called flower mapping.

There are several management strategies for optimal runner control.   These include:

Manual Runner Removal

-In Plasticulture systems, where strawberries are grown on raised beds covered with plastic mulch, runners should be removed as soon as they appear.

-Leaving runners attached can drain the mother plant’s resources, reducing overall fruit production.

-Regular runner removal every 2–3 weeks during the growing season is recommended.

Selecting Cultivars with Moderate Runner Production

-Some cultivars naturally produce more runners than others. If runner management is a challenge, selecting a variety with lower runner production may reduce labor costs and improve fruit yield.

-Nursery catalogs often list the runnering tendencies of different cultivars, helping growers make informed choices.

Photoperiod Manipulation

-In controlled environments (such as greenhouses or high tunnels), altering the day length using artificial lighting or shading can help control runner formation.

-For short-day varieties, extending daylight exposure can suppress flower bud formation and encourage runners.

-For long-day varieties, ensuring adequate long-day conditions during the early growth stages can improve flowering.

Adjusting Nitrogen Applications

-Reduce nitrogen application before flower bud initiation to prevent excessive runner formation.

-Apply nitrogen one week after the first flower buds appear to encourage more fruiting potential.

Using Mechanized Runner Removal

-While manual runner removal is labor-intensive, researchers and engineers are developing automated solutions to mechanize this process.

-Some trials with runner-cutting robots show promise, though widespread commercial adoption remains a challenge due to cost.

I would really like to thank Dr. Edward Durner for taking time out of his schedule to join us on Zoom for the 2025 Nova Scotia Horticultural Congress.  It takes a really good presenter to give such an in-depth presentation while in the throughs of Covid.  We wish him a speedy recovery.