Removal of leaves, runners and flowers is a key crop management practice for hydroponic strawberry to balance sink/source and vegetative/reproductive growth. Leaf pruning is for controlling leafiness to optimize light interception and is a typical key practice of greenhouse crop production including for tomato and pepper. Removing old leaves that are no longer contributing to the fruit production would help maximize the allocation of photoassimilates to other sinks, including fruit.

Leaf pruning is conducted mainly to remove old leaves that are no longer contributing to the carbohydrate production. When strawberry leaves become old, they lose their glossiness and begin to turn yellow. Leaving dead leaves on the plant is not recommended since it could prevent air circulation within the canopy and be a host for disease. Runners are also removed to prevent allocation of photoassimilates to these unwanted sink organs.  However, under optimum growing conditions, runner production should be minimum.

Flower pruning is usually conducted 1) when vegetative growth is preferred to reproductive growth and 2) when the flower cluster no longer produces large flowers but many small flowers.  When rooted runner plants and dormant runner plants are used, these transplants need to establish a large crown (a minimum of 10 mm in diameter) with five or more leaves before allowing them to set fruit. Therefore flower clusters developed during this stage are topically removed as shown in the figure. Flower size is correlated with fruit size and leaving many small flowers results in wasted photoassimilates (sugars produced by photosynthesis) by producing unmarketable small fruits.  Fruit pruning may be also conducted in order to attempt to increase the fruit size by mitigating competition among sinks. Although fruit size is reportedly negatively correlated with number of fruits developed per plant (Rindom et al., 1995), the efficacy of this technique seems inconclusive, and the practice of fruit pruning is not as widely conducted as with other greenhouse crops such as tomato. 

Crown pruning is a somewhat unique practice. Strawberry plants develop extended shoots (or crowns) from one or more axillary buds. In Japan, crown pruning has been conducted to maintain an ideal crown density in the production rows inside the greenhouse during the winter production. Crown pruning is also anecdotally known as an effective tool to induce flower bud development. However removing young crowns can also set back the plant growth. Therefore crown pruning for flower induction should be conducted only when plants are overly vegetative.

Rindom, A. and P. Hansen. 1995. Effects of fruit numbers and plant status on fruit size in the strawberry. Acta Agric Scand. Sect. B. Soil and Plant Sci. 45:142-147.

Updated (6/14/14)