The evergreen wisteria (Millettia reticulata) is a vigorous woody vine that provides year-round foliage, unlike its deciduous relatives. Because it retains its leaves, its winter care must account for ongoing water loss, making its needs distinct. Originating from warmer regions, Millettia reticulata is considered semi-evergreen in USDA Hardiness Zones 8 through 10. The goal of winter care is to protect the plant’s root system and above-ground structures from damaging cold and drying winds.
Shielding Against Cold and Frost
The primary concern for evergreen wisteria is damage from sustained temperatures below 15°F, which can cause significant dieback. The root zone requires insulation to buffer the soil against hard freezes. Apply a 4-to-6-inch layer of organic mulch, such as shredded bark or straw, around the base of the plant to regulate soil temperature and retain warmth. This protective ring should extend to the dripline, but never be piled directly against the main stem.
Windburn, or desiccation, poses a major threat because evergreen leaves continue to lose moisture even when the ground is frozen. To mitigate this, erect a temporary screen of burlap or a breathable frost cloth on the windward side during periods of extreme cold. This barrier breaks the wind’s drying effect without blocking necessary sunlight. Container specimens are highly susceptible to root freezing and should be moved to a sheltered location, such as an unheated garage or against a warm, south-facing wall.
Managing Winter Hydration and Nutrients
The vine’s growth slows dramatically in winter, but its evergreen nature means it continues to lose water through transpiration. Watering needs are significantly reduced, but the plant must not be allowed to dry out completely. Before a predicted hard freeze, provide a deep, thorough watering; this helps warm the soil and offers a reserve of moisture for the roots.
During dry winter spells, check the soil moisture by inserting a finger or trowel two to three inches deep near the root zone. If the soil feels dry, a moderate watering prevents desiccation damage to the leaves. Fertilization must cease entirely once the growing season ends in fall. Feeding the vine in winter encourages tender new growth highly susceptible to frost damage.
Late Winter Pruning and Cleanup
Late winter is the ideal time for structural cleanup before spring growth begins. Inspect the entire vine for stems that appear dead, diseased, or damaged from the cold. Removing this winter-killed material improves the plant’s health and prepares it for a vigorous growing season. Make clean cuts just above a healthy bud or where the damaged wood meets live wood.
Major structural shaping or heavy reduction pruning should wait until spring or after the main flowering period. However, light trimming can be done now to establish a strong framework and allow better air circulation through the dense foliage. This timing also allows for a final inspection for any overwintering pests or fungal issues before new foliage emerges.