Begonias are a diverse genus, comprising over 2,000 species and countless hybrids originating from tropical and subtropical regions. Because of this genetic diversity, when a begonia flowers depends entirely on the specific variety and its environment. Whether grown as a summer annual outdoors or maintained as a perennial houseplant indoors dictates its individual flowering calendar. Begonias are typically categorized into groups based on their root structure to understand the blooming cycle.
Seasonal Flowering Patterns by Begonia Group
Tuberous Begonias
Tuberous begonias are prized for their large, spectacular flowers and operate on a strict seasonal schedule. These varieties bloom prolifically throughout the summer, typically starting in June and continuing until the first autumn frost. The plant focuses energy on producing flowers and storing nutrients in its underground tuber during this season. To achieve earlier blooms, gardeners often start the tubers indoors in late winter before moving them outside after the last frost.
Fibrous/Wax Begonias (Semperflorens)
Fibrous or wax begonias (Begonia semperflorens) are known for their near-continuous flowering habit. The Latin name translates to “always flowering,” accurately describing their nature. When grown outdoors as annuals, they produce flowers reliably from late spring through the first hard frost. If kept indoors in a warm, brightly lit environment, this group can maintain blooming year-round, as they do not require a dormancy period.
Rhizomatous Begonias
Rhizomatous begonias, including the popular Rex types, are generally cultivated more for their striking, ornamental foliage than their flowers. They produce blooms on tall stalks held above the leaves, typically appearing during the late winter or early spring months. Their blooming schedule is distinct from summer-flowering types, offering color when many other garden plants are dormant.
Environmental Factors that Initiate Blooming
For many begonias, the length of the day, known as the photoperiod, is a primary cue. Tuberous begonias are considered long-day plants, requiring extended periods of light to encourage active growth and flowering. Conversely, some winter-blooming types, like Rieger begonias, are short-day plants, initiating flower bud formation when daylight hours begin to decrease.
Temperature
Temperature also plays a significant role in flower production. Begonias thrive and produce the most abundant blooms within a comfortable temperature range, typically between 60 and 75°F. Temperatures consistently exceeding 80°F or dropping below 55°F can cause flowers to abort, a phenomenon known as bud blast. Maintaining a stable, moderate temperature is linked to sustained flower development.
Dormancy
A period of dormancy is a physiological trigger for the next season’s bloom cycle in tuberous begonias. As temperatures cool and daylight shorten in the fall, the plant directs its energy into the tuber, signaling a rest period. This cool, dry rest allows the plant to reset its system and is necessary for it to produce viable, vigorous flowers the following summer. Without this required break, the subsequent bloom cycle may be severely diminished.
Practical Steps for Sustained Flowering
Deadheading
Deadheading, the removal of spent or faded flowers, is an effective maintenance practice to maximize and prolong the flowering period. By removing blooms before they have a chance to set seed, the plant’s energy is redirected from reproduction into producing new flower buds. This simple practice ensures the plant continues its bloom production cycle.
Fertilization
Proper fertilization is necessary to fuel the heavy energy demands of continuous blooming. During the flowering period, use a fertilizer formulation higher in phosphorus (P) and potassium (K) than nitrogen (N). Ratios like 5-10-5 or 10-10-10 encourage flower production and root health, while excessive nitrogen promotes foliage growth at the expense of blooms. Apply a diluted, water-soluble fertilizer every two to four weeks during the active growing season.
Water and Humidity Management
Consistent water and humidity management are important for preventing flower loss. Begonias require a steady supply of moisture but are susceptible to root rot if overwatered. The soil should be kept evenly moist, but allowed to dry slightly at the surface between waterings. For many varieties, particularly those grown indoors, maintaining moderate humidity levels, ideally above 40%, helps prevent delicate buds and flowers from dropping prematurely.