Winter injury to ornamental plants can vary yearly, by location, and by plant species. The severity of the damage depends on factors such as the type of plants, their planting locations, the region's climate, the mildness or severity of the season, and the preventive measures taken in the fall.
Plant injuries can result from a single factor or several factors. For example:
- Sunlight and drying winds can desiccate foliage, leading to discoloration and leaf drop.
- Extremely low temperatures may injure or kill plants. Sudden warm temperatures on a tree trunk's south or southwest side, followed by extremely cold temperatures, can result in bark splitting.
- Alternating freezing and thawing periods can cause perennials and newly planted shrubs to heave from the ground.
- Ice and snowstorms can break branches.
- During winter, ornamental plants are often at risk from rabbits and mice, particularly during heavy snow cover.
To protect nearly all ornamentals, several precautions should be taken:
1. **Soil Conditions:** Plant in well-drained sites to avoid excessive moisture that could damage roots. Before the soil freezes in autumn, thoroughly water the plants, especially if the summer or fall has been dry. Research indicates that fertilizing in October or November is beneficial, and this should be supplemented with spring fertilization for optimal growth. * Only use a starter fertilizer on newly planted plants planted in the ground for less than a year.
2. **Specific Precautions for Individual Plants:** In late autumn or early winter, take measures such as wrapping, spraying, mulching, or tying plants to reduce winter injury.
- **Protect Trees by Wrapping:** Newly planted or tender trees, especially those located near sun-reflecting walls, should be shielded during their first winter or two to prevent sunscald. The tender bark on a southern surface can warm substantially, and sudden freezing temperatures can cause it to split. Wrap tree trunks with commercially available tree wrap to guard against this.
- **Protect Evergreens with Sprays or Wrappings:** Narrow-leaved and broad-leaved evergreens can lose moisture through their leaves even in winter. Since soil moisture is often frozen, the plants cannot replenish lost moisture, leading to browning and leaf drop in sensitive species like hollies, rhododendrons, and azaleas. To minimize desiccation injury, spray the plants in early December and again in early February with an anti-desiccant like Wilt Stop, which forms a protective film on the foliage to reduce drying from wind and sun. Furthermore, protect evergreens near driveways or highways from moisture-containing de-icing materials by shielding them with burlap or canvas, ensuring that some light can still reach the plants.
- **Protect Shrubs and Perennials with Mulch:** Apply mulch after the ground freezes to maintain a cold soil temperature. This reduces the risk of heaving caused by freezing and thawing cycles. Mulch also helps retain soil moisture. Avoid using materials like maple leaves, which can compact and become moldy; instead, opt for alternatives like oak leaves, peat moss, or bark mulches. Pine boughs or Christmas tree greens can protect evergreens from wind and sun while serving as mulch.
- **Protect Evergreens by Tying:** Plants with multiple leaders, such as upright junipers or arborvitae, can suffer from damage caused by snow or ice. To prevent breakage, secure the trunk with heavy twine, starting at the base and winding it spirally to the top and then back down in reverse.
- **Protect Trees and Shrubs from Rodents:** Certain plants, such as flowering crabapples, mountain ashes, hawthorns, viburnums, and winged euonymus, are familiar food sources for rabbits and mice. Injuries can create access points for borers and diseases, potentially leading to the plant's death. Protect the trunk or main stem with a 1/2-inch mesh wire cloth collar or plastic arbor guards extending from the soil line up to 2 to 3 feet in height. Additionally, trunks can be sprayed or painted with a rodent repellent when temperatures rise above 40 degrees Fahrenheit.
By following these guidelines, you can help ensure the health and longevity of your ornamental plants throughout the winter season.