Begonias are tender perennials typically grown as annuals in cooler climates because they cannot tolerate freezing temperatures. Overwintering protects these plants from frost, ensuring survival and vigorous regrowth the following season. Successful overwintering requires different approaches depending on whether the variety is kept actively growing or forced into dormancy.
Preparing Begonias for Winter Transition
The preparation phase begins well before the first expected frost, typically when nighttime temperatures start dropping consistently below 50 degrees Fahrenheit. This timing minimizes shock and begins reducing the plant’s active growth. About six weeks before the move, gradually reduce the frequency of watering to signal the plant to slow its metabolism.
Before bringing any plant indoors, a thorough inspection and sanitation process is necessary to prevent introducing garden pests. Examine the foliage and soil for common hitchhikers like aphids, spider mites, or fungus gnat larvae. Pruning back the stems by about one-third helps manage the plant size and remove any damaged or diseased foliage.
If pests are discovered, treating the plant with an insecticidal soap or a gentle stream of water is advisable before the move. This initial clean-up is important for varieties grown as houseplants, as the dry indoor air can stress the plants and make them more susceptible to infestation.
Storing Dormant Tuberous Begonias
Tuberous begonias, known for their large, showy flowers, require cold dormancy to rest and recharge for the next growing season. This process begins by allowing the foliage to die back naturally after the first light frost, which signals the plant to transfer its energy into the underground tuber. Once the leaves have yellowed, the stems should be cut back to about one to two inches above the soil line.
The next step involves carefully digging up the tubers, ensuring not to damage the fragile growth points. After lifting them, the tubers must be cured by letting them dry on a screen or newspaper in a frost-free, dry, and well-ventilated area for one to two weeks. This process allows the outer skin to harden and heal minor wounds, significantly reducing the risk of rot.
Once cured, gently brush off any remaining dry soil and remove the last remnants of the stem and roots. The ideal storage medium is a breathable material like peat moss, vermiculite, or dry sawdust, which helps regulate moisture. The tubers should be nestled into a cardboard box or paper bag, ensuring they do not touch, and then covered completely with the medium.
The storage location must be dark, dry, and consistently cool, with temperatures maintained between 40 and 50 degrees Fahrenheit. Temperatures below 40 degrees Fahrenheit risk freezing the tubers, while temperatures above 50 degrees Fahrenheit may cause them to break dormancy too early. Checking the tubers monthly for signs of shriveling (too dry) or mold (too moist) is recommended throughout the winter.
Managing Fibrous and Wax Begonias Indoors
Fibrous and wax begonias (cane-type and bedding varieties) do not form tubers and are overwintered as active houseplants. They must be moved indoors before the first frost, ideally when nighttime temperatures are still above 55 degrees Fahrenheit, to minimize cold shock. They should be placed in a location that receives bright, filtered light, such as a south- or east-facing window, or under supplemental grow lights for 10 to 12 hours a day.
The dry air typical of heated indoor environments can be challenging, so managing humidity is important. Placing the pots on a pebble tray filled with a shallow layer of water (ensuring the pot bottom does not touch the water) helps increase the local humidity as the water evaporates. Consistent temperatures, away from cold drafts or direct heat vents, are necessary for healthy growth.
During the winter months, the plant’s growth rate naturally slows due to shorter daylight hours, so watering frequency must be significantly reduced. The soil should be allowed to dry out slightly between waterings to prevent root rot. Fertilizer application should be stopped entirely or applied at a greatly reduced strength, as the plant is not in its active growth phase.
Transitioning Begonias Back to Spring Growth
The transition back to outdoor life begins indoors several weeks before the last expected spring frost, typically around late February or early March. Tuberous begonias should be removed from storage and planted hollow-side up in shallow trays filled with slightly moistened potting mix or peat moss. Placing these trays in a warm area (65 to 75 degrees Fahrenheit) encourages the tubers to sprout.
Once the initial sprouts are visible, usually within a few weeks, the tubers can be transplanted into individual pots and moved to a bright, indirect light location. Watering should remain light until the stems and leaves are fully developed, ensuring the soil is never soggy. This head start allows the plants to develop a strong root system before moving outside.
For the fibrous and wax begonias kept actively growing indoors, the transition requires hardening off. About two weeks before the planned outdoor move, these plants should be gradually introduced to the outdoor environment, starting with a few hours each day in a shaded, protected location. This gradual exposure to sunlight, wind, and temperature fluctuations prevents leaf scorch and shock.
The final move outdoors should only occur once all danger of frost has passed and nighttime temperatures are consistently above 50 degrees Fahrenheit. Both the sprouted tubers and the hardened-off houseplants will benefit from placement in their final summer location, typically an area with bright, indirect light to avoid burning the new, tender foliage.