By Fanny Iriarte
Extension Plant Pathology
Iowa State University
Plants that are well maintained during the year (proper pruning, watering and fertilizing) and that are healthy will be better candidates for winter survival. Winter conditions can kill plants in many ways, even some cold hardy plants. Their tops or roots may freeze. Some evergreens that do not have enough water supply in the soil may dry out when subjected to persistent winds.
Sometimes, roots are damaged by alternate freezing and thawing. For many plant species, winter protection is essential. However, protecting too early can interfere with the plant’s natural ability to adjust for winter or “harden off.”
Do not fertilize or prune plants at this time of the year as this will encourage new succulent growth and tender young branches will not be ready to face the cold winter months. In late fall, after the leaves have died, pick off remaining leaves and fruits from the stems and pick up as many dead leaves from the ground as possible. Fungal spores overwinter on dead leaves and mummified fruits in the case of plum, cherry and apple trees.
Do your best to reduce your plant disease problems next spring by using good sanitation practices during the fall and removing infected plant material. Removing fallen infected needles of blue spruce and pine will greatly reduce the amount of fungal inoculum for Rhizosphaera needle cast and Dothiosthroma and Diplodia tip blight diseases. Raking up leaves of maple, oak, peach and apple trees will greatly reduce fungal inoculum of maple leaf blister and anthracnose disease, bur oak blight, peach leaf curl and apple scab diseases.
Water plants as needed in the fall and make sure you give your plants a good watering just before the ground freezes as plants can suffer as much from dehydration as from cold during the winter. Mulching trees and shrubs with organic mulches is a good practice not only to help conserve moisture but also to help keep the soil well aerated and protect roots from extreme cold temperatures. The mulched area around trees should include as much of the root zone as possible.
Last year a large number of boxwood suffered winter kill. It will be wise to protect these plants from winds, snow and ice this winter by covering with some kind of protective material.
There is abundant information online about protecting plants from winter. The University of Illinois Extension site has information on how to protect roses over winter. Another interesting site is the Fine Gardening Magazine website that offers detailed information and ideas about protecting plants for the winter months.
In early spring prune off dead branches and/or cankered branches and provide moisture and balanced fertilization. Remember, less stressed plants better stand attack by insect pests and diseases.