Fall and Winter Watering
by J.E. Klett and C. Wilson adapted by John Meshna
• Water trees, shrubs and lawns during prolonged dry fall and winter periods to prevent root damage that affects the health of the entire plant.
• Water only when air and soil temperatures are above 40 degrees F with no snow cover.
• Established large trees have a root spread equal to or greater than the width and sometimesw the height of the tree. Apply water to the most critical part of the root zone within the dripline.
Dry air, low precipitation, little soil moisture, and fluctuating temperatures are characteristics of fall and winter in many areas of the north. There often can be little or no snow cover to provide soil moisture in winter nowadays thank to climate change, particularly from October through February. Trees, shrubs, perennials and lawns can be damaged if they do not receive supplemental water.
The result of long, dry periods during fall and winter is injury or death to parts of plant root systems. Affected plants may appear perfectly normal and resume growth in the spring using stored food energy. Plants may be weakened and all or parts may die in late spring or early summer when temperatures rise. Weakened plants also may be subject to insect and disease problems.
- Plants Are Sensitive to Drought Injury
Woody plants with shallow root systems require supplemental watering during extended dry fall and winter periods. These include European white and paper birches; Norway, Silver, Red and Maples; Lindens, Alder, Hornbeams, Dogwood and Mountain Ash. Evergreen plants that benefit include Spruce, Fir, Arborvitae, Yew, Oregon Grape-holly and Euonymus. Woody plants benefit from mulch to conserve soil moisture.
Herbaceous perennials in exposed sites are more subject to winter freezing and thawing. This opens cracks in soil that expose roots to cold and drying. Winter watering combined with mulching can prevent damage.
Lawns also are prone to winter damage. Newly established lawns, whether seed or sod, are especially susceptible to damage. Susceptibility increases for lawns with south or west exposures.
- Watering Guidelines
Water only when air temperatures are above 40 degrees F. Apply water at mid-day so it will have time to soak in before possible freezing at night. A solid layer (persisting for more than a month) of ice on lawns can cause suffocation or result in matting of the grass.
Plants receiving reflected heat from buildings, walls and fences are more subject to damage. The low angle of winter sun makes this more likely in south or west exposures. Windy sites result in faster drying of sod and plants and require additional water.
Monitor weather conditions and water during extended dry periodsone to two times per month without snow cover.
- Newly Planted vs. Established Plants
Newly planted trees are most susceptible to winter drought injury because they haven't had time to put out and extended root system yet. Woody trees generally take one year to establish for each inch of trunk diameter. For example, a two inch diameter (caliper) tree takes a minimum of two years to establish under normal conditions.
Trees obtain water best when it is allowed to soak into the soil slowly to a depth of 12 inches. Methods of watering trees include: sprinklers, deep-root fork or needle, soaker hose or soft spray wand or just a plain old watering can with the rosette taken off. Apply water to many locations under the dripline and beyond if possible. If you use a deep-root fork or needle, insert no deeper than 8 inches into the soil. As a general survival rule when the soil is extremely dry apply 10 gallons of water for each diameter inch of the tree. For example, a two-inch diameter tree, needs 20 gallons per watering. Use a ruler to measure your tree’s diameter. If the soil already has some moisture in it just water until the ground is soaked but not puddling on the surface.
Newly planted shrubs require more water than established shrubs that have been planted for at least one year. The following recommendations assume shrubs are mulched to retain moisture. In dry winters, all shrubs benefit from winter watering from October through March. Apply 5 gallons two times per month for a newly planted shrub. Small established shrubs (less than 3 feet tall) should receive 5 gallons monthly. Large established shrubs (more than 6 feet) require 18 gallons on a monthly basis. Decrease amounts to account for precipitation. Water within the dripline of the shrub and around the base.
Herbaceous perennial establishment periods vary. Bare root plants require longer to establish than container plants. Plants transplanted late in the summer or fall will not establish as quickly as plants planted in the spring. Winter watering is advisable with late planted perennials, bare root plants, and perennials located in windy or southwest exposures.
If your plants show signs of nutrient deficiency in the fall you can fertilize them but stay away from high nitrogen applications. You're not trying to make them grow at this time of year. You're trying to prepare them for next spring and the cold months ahead, so provide them with low or no nitrogen fertilizers and biologically active products to help them store nutirents for the winter in the roots and be ready for growth in the spring. Organica "Kelp Booster", "Microbial Soil Conditioner", "Biotmatrix", "Plant Growth Activator Plus" , "Alfalfa Meal" and Kelp are recommended.
Light pruning of dead and diseased parts of the plants can be done in early fall but don't prune off large limbs and lots of tissue unless there's some really good reason to do so. Exposed tissue can be damaged by the cold and dry winds of the winter and won't heal over as fast in the fall leaving time for pathogens to get inside of the plants. Pruning times and regiments vary between different types of plants so a little research a head of time will help you figure out what to do.