Winterizing Turf

OMAF Turfgrass Series (1997)

Table of Contents

• Low Temperature Injury
• Cultural Practices
• Principles of Late Season Fertilization
• Timing and Rates

Low Temperature Injury

Early fall is the time to think about putting your turf to rest for the winter. In order to best understand what needs to be done to avoid winterkill it is necessary to have a good understanding of what winterkill is.

Winterkill can be caused in three different ways namely:

• direct low temperature stress/crown hydration
• winter desiccation
• injury caused by low temperature fungi

The main cause of winter injury is direct low temperature kill.

What mechanisms do plants have for achieving winter hardiness? The turfgrass plant becomes more winter hardy by storing sugar in its cells and hence lowering the level of water in the plant. A cell with a high sugar content is more resistant to freezing than one with a low sugar content. A good analogy is a bottle of juice will take longer to freeze than a bottle of water. We need to help the turfgrass plant store sugar in its cells.

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Cultural Practices

The key principle is maintaining a low level of water in the crown of the plant. There are several cultural practices which accomplish this.

1. The first step in prevention of low temperature injurycrown hydration is to provide adequate surface drainage. Turfgrass that is surrounded by water in the winter will take up water which makes it more prone to internal freezing.
2. Controlling thatch is also important. Thatch harbours disease causing organisms such as snow molds. Additionally, in turf with excessive thatch the crowns are elevated above the soil and hence subjected to greater extremes in temperature.
3. Raising the mowing height can help increase low temperature hardiness. By raising the mowing height the crown of the plant is less exposed to extreme temperatures. Also the additional plant material serves as insulation for the crowns. What should be avoided is excessively long turf going into the winter. If the grass is too long a perfect environment for low temperature fungi is created.
4. The nutritional status of the turfgrass plant greatly influences low temperature hardiness. Adequate levels of potassium and phosphorus as well as late season nitrogen fertilization are important in ensuring low temperature hardiness.

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Principles of Late Season Fertilization

1. Nitrogen is taken up by the roots even though shoot growth has ceased. This is because roots remain active at cooler temperatures than shoots.
2. Nitrogen enhances fall colour and hence increases chlorophyll content.
3. Increased chlorophyll content means increased photosynthesis.
4. Increased photosynthesis means increased sugars. Since turf is not growing at the time of the fertilizer application the sugars which are produced are not used for growth but stored to enhance winter survival and spring recovery.
5. Late season nitrogen promotes deep rooting during fall. Plants go into spring and summer with deeper, healthier roots.
6. Spring green up is early because the nitrogen stored in the roots is there ready when shoot growth resumes.

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Timing and Rates

The late season fertilizer application should take place when turf is green but no longer growing. Timing is critical. If it is applied too early it will induce succulent lush growth in the fall which will be susceptible to winter injury. If applied too late it will be of no benefit to the turf. The timing for the Guelph area is late October to early November.

Research has shown that a high nitrogen/low potassium fertilizer at 1 to 1.5 kg of N per 100m² gives the best results. Because of the difficulty applying a liquid fertilizer at this time of year ie. freezing tanks, pumps, etc., it is best to apply a granular fertilizer. If a fall fertilization program is utilized spring fertilization can be delayed until late May.

Cultural practices such as insuring adequate surface drainage, thatch control, raising mowing height and application of potassium and a late season application of nitrogen will result in good winter survival, early spring green up, deep roots which will withstand summer stress conditions.

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