Hydrangeas & Freezing

Growing Zones

• The United States Department of Agriculture separates the United States into eleven zones that reflect the hardiness of plant life in varying conditions. Zone maps provide a way for gardeners to compare the places where a plant thrives versus the gardener's location. Hydrangeas grow in zones 1 through 9. The plant performs poorly in zones 1 through 3 due to extreme temperatures and frequent frost. Frost will damage the plant, including the cold hardy varieties, if it is not protected.

Damage

• Hydrangea damage from freezing temperatures varies with frost amounts, the species and the location in the landscape. Minor damage includes the stunting of flower growth. A hard frost in the late spring damages emerging growth, resulting in poor structure and few, if any, blooms. The extent of frost damage depends on how many buds are affected. A damaged bud can cause an entire branch to die off.

Garden Hydrangeas

• A garden hydrangea needs close monitoring during spring and fall months, when unexpected frost occurs. The plants require protection from early or late freezing temperatures. Cover the plants with an old bed sheet or plastic when temperatures may reach freezing. The extent of damage that frost causes depends on the species of hydrangea. Hydrangea paniculata features cold hardiness characteristics, making it a popular option for growers in regions with harsh winters. Hydrangea macrophylla, by contrast, does not tolerate cold temperatures. If a hydrangea falls victim to frost in the spring, prune off any obviously damaged buds or stems. Prune down one-third of the plant's growth in late fall or early winter for strong spring growth.

Potted Hydrangeas

• Potted hydrangeas require the same protection from freezing temperatures as garden varieties. The potted plant kept indoors or outdoors on a porch or patio requires overwintering. According to Cornell University, give the plant six weeks of below 65 F temperatures before the stems lose leaves. After the leaves drop off, allow the plant to sit in temperatures of 35 to 45 F at night for six weeks. Bring the plant inside and place it in a cool area like a basement for the remainder of the winter season.