Pruning basics

Removal of leaves, runners and flowers is a key crop management practice for soilless culture of strawberry to balance sink/source and vegetative/reproductive growth.

Leaf pruning is for controlling leafiness to optimize light interception and is a typical key common practice of greenhouse fruiting crop production (e.g., tomato). Removing old leaves that are no longer contributing to the fruit production would help maximize the allocation of photoassimilates to other sinks, including fruit.

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.

Runner pruning. Runners are also removed to prevent allocation of photoassimilates to these unwanted sink organs.  However, under optimum growing conditions, runner production should be minimum or none during fruit production. When you see more runners, it means that plants are turning valuable buds to develop runners instead of extended crowns (new shoots) or flower clusters. Nurient solution, lighting, and temperature need to be corrected to reduce runnering.

Strawberry plants extending runners to be removed.

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 typically removed. Small flowers produce small fruits. Leaving too 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. However, according to an expert, “the impact of the current pruning only reflects the next cluster fruit size, rather than the remaining fruits of the same cluster”. It is also one of labor-intensive practices of strawberry production under controlled environment. Number of flowers per truss and therefore the fruit size are a cultivar-specific trait. Therefore cultivars that tend to produce too many small flowers can be avoided.

A typical stage to consider flower pruning, remaining 7-10 flowers per cluster. The number of flowers per cluster is cultivar- and greenhouse-climate specific. This particular grower leaves 7 flowers (one king flower plus two 3-flowered trusses) for ‘Nyoho’ strawberry.

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.

Photos showing crown pruning where an old unwanted crown was snapped off from the base.