Ministry of Agriculture and Land
Optimum Growing Conditions Prevent Winter Injury
Hannah Mathers, 05/96
As major as the market losses were this spring due to weather, the losses may extend beyond this year and into the next. Any stress during the growing season can predispose a perennial plant to winter damage. Winter damage, however, does not always show up as direct injury. Freezing temperatures, that are not sufficient to kill, can cause a plant to be predisposed to other problems such as bacterial blight, phytopthora root rot, and several other pest problems.
Start to think early on about minimizing stock loses due to winter injury. The best way to prevent winter injury is to ensure maximum acclimation. By optimizing growing conditions during the growing season and minimizing stressful conditions. Supplying adequate moisture and balanced nutrition are essential.
Moisture
Moisture can have a considerable effect on hardiness. If moisture is withheld during the summer, hardiness is increased as a result of growth cessation (Glerum 1976). Prolonged droughts in summer , however, should be avoided by irrigation, as should any kind of stress, since they will interfere with the physiological processes, which in turn interfere with the cold acclimation process (Levitt 1982).
Compared with the shoots, roots have relatively high moisture percentages (Pellet and White 1969). Hardy plants lose water in the fall (Levitt 1980). Water binding substances have been noted to inhibit cellular dehydration during water movement to regions of intracellular ice formation (Levitt 1980). Cells having a higher percentage of bound water due to less actual moisture have greater tolerance to freeze damage. On the basis of shoots having lower moisture percentages than roots, greater hardiness would develop in the shoots. The decrease in shoot moisture is caused by an increase in bound water resulting from an actual increase in water binding substances (Pellet and White 1969; Levitt 1980).
Nutrition
Nitrogen tends to reduce hardiness or prevent the cold acclimation process (Fuchigami and Weiser 1981), while potassium and phosphorus tend to increase hardiness (Pellet 1973). Nutrients stimulate or reduce the rate of growth in woody plants and thus affect cold hardiness indirectly. Nitrogen stimulates growth, and when applied late in the growing season can prevent growth cessation and thus reduce the potential for cold hardiness in a woody plant. Nitrogen can also improve hardening when applied after bud set (Glerum 1976). Conversely, potassium and phosphorus can assist in growth cessation and bud development (Pellet 1973). The amounts of nutrients, their relative proportion to each other, timing of application, and availability of moisture for uptake are all significant (Glerum 1976; Pellet 1973).
Pellet and Carter (1981), after a critical review of the literature, determined three conditions must be met for nutrient levels to be of concern in plant cold hardiness. First, the plant must be growing in a marginal area for it's photoperiod requirements to be met. As a result , the critical photoperiod for triggering acclimation will not be reached until very late in the season. Second, temperature must be maintained at sufficiently high levels to support continual growth and prevention of acclimation until late in the growing season. Third, an early severe freeze must be encountered before acclimation has proceeded sufficiently.
The widely-held belief that fertility may predispose plants to severe winter injury is not universally supported by research data. Most plants fertilized at levels which promote optimum growth will cold acclimate at a similar rate and to the same degree as plants grown under a lower fertility regime, and may even exceed cold hardiness development of plants grown under severe nutrient deficiencies. Extremely high levels of fertility, however, can retard cold acclimation (Pellet and Carter 1981; Pellet 1973; Pellet and White 1969).
Conclusions
Although several other environmental factors besides nutrition and moisture play important roles in cold acclimation, what the nursery grower or landscaper does in these two areas during the growing season will significantly impact the direct and indirect plant losses in the subsequent spring.
Brierly and Landon (1946) reported that a well grown plant in good health, not weakened by insects, disease or excessive production will survive cold stress better than a plant in poor condition and what was true in 1946 is just as true today.
References
Brierly, W.G. and R.H. Landon. 1946. PASHS 47:224-233.
Fuchigami, L.H. and Weiser, C.J. 1981. JASHS 106:140-143.
Glerum, C. 1976. In Tree physiology and yield improvement pp. 403-420.
Levitt, J. 1980. In Vol. 1. Chilling, freezing, and high temperature stresses.
Levitt, J. 1982. pp. 3-10. In Vol. 1. Plant cold hardiness and freezing stress.
Pellett, N.E. 1973. JASHS 98:82-86.
Pellett, H.M. and J.V. Carter. Hort. Rev. 3:144-171.
Pellett, N.E. and D.W. White. 1969. JASHS. 94:453-456.
