Pollination is the necessary process of transferring pollen from the male part of a flower to the female part, which is required for fertilization and subsequent fruit development. While strawberry flowers are equipped with both male and female structures, they cannot produce fruit without this transfer occurring. Growing strawberries indoors eliminates the natural agents of pollination, such as wind or insects like bees. This means that for a successful harvest of indoor strawberries, you must manually intervene to ensure the pollen reaches the receptive female flower parts.
Recognizing Flowers Ready for Pollination
A strawberry flower is ready for pollination when its white petals have fully opened. The center contains all the reproductive structures, including the numerous yellow, dust-covered anthers, which are the male parts holding the pollen. The large, dome-shaped structure in the center is the receptacle, which will eventually swell to become the fleshy fruit. This receptacle is covered in tiny, hair-like projections called stigmas, which are the receptive female surfaces. The stigma is most receptive to pollen during the first one to two days after the flower has completely opened.
Manual Pollination Techniques
Since the male anthers and female stigmas are separated, you must physically bridge this gap to ensure fertilization. The goal of manual pollination is to gently and evenly distribute the pollen from the anthers across the entire surface of the central receptacle. Incomplete pollen transfer results in small, misshapen fruit, because the berry only swells in areas where the individual ovules have been successfully fertilized.
One accessible and precise method is using a small, soft-bristled paintbrush or a cotton swab. Gently swirl the brush across the yellow anthers to pick up the visible pollen grains. Immediately after collecting the pollen, lightly brush the central, dome-shaped stigma structure, ensuring that you cover the whole surface.
Another method involves mechanical vibration, which mimics the action of wind or a buzzing bee. A soft-bristled electric toothbrush, held against the stem of the flower, can cause the necessary vibration to dislodge the pollen. For best results, repeat the pollination process daily for two to three days on each newly opened flower to ensure that every part of the stigma is covered.
Essential Care After Pollination
Once a flower is pollinated, the plant requires specific environmental conditions to support the development of the fruit, known as fruit set. Adequate light is paramount, and indoor setups should use full-spectrum LED grow lights for 12 to 16 hours daily. For optimal growth and fruit quality, the light intensity should ideally be between 12 and 25 moles per square meter per day.
Temperature control is also important, with daytime temperatures maintained between 68 and 75°F. A drop in temperature at night, into the range of 50 to 54°F, is beneficial for encouraging larger fruit size and better flavor. Maintaining moderate humidity, specifically between 40% and 60%, helps prevent issues like tip burn and fungal diseases.
The first sign of successful pollination is the fading of the white petals, followed by the central receptacle beginning to swell into a small, green berry. If pollination fails, the flower will simply shrivel and die instead of forming a fruit. As the plant shifts energy toward fruit production, its demand for water and nutrients increases, so ensure the soil remains consistently moist and apply a balanced liquid fertilizer every three to four weeks.