Come winter, yard care in the Islands should take on a subtle — but significant — change of pace.

December, January and February bring cooler night temperatures and shorter days, which affect the growth rate of our warm-season turf grasses as well as many tropical trees and shrubs. Winter's weather changes are magnified at higher elevations but can be noticeable even at sea level. Knowing what to expect and how best to deal with the seasonal fluctuations can be a big help in maintaining a nice-looking yard.

As evening temperatures fall to the high 60s, many turf-grass species, particularly Bermuda grass and seashore paspalum, grow more slowly due to a reduced rate of photosynthesis. Lower carbohydrate reserves eventually lead to a shallower root system, which stresses the turf even more. The result: a weaker lawn that's more susceptible to weed invasion and damage from foot traffic.

When temperatures drop to the mid- to low-60s, a Bermuda-grass lawn may go into temporary dormancy — it stops growing and may even turn brown. If this happens, resist the temptation to pile on the fertilizer and water. Just wait until the temperatures improve. The grass will survive.

Basically, winter stresses your lawn out. Here are a few maintenance tips.

Mowing always puts a temporary stress on the grass. Since the lawn is growing more slowly, you can mow less often. Don't remove more than one-third of the leaf growth at each mowing. This is also a good time to raise the height of cut a notch or two. This will allow more photosynthetic activity for the leaves and provide the roots with more carbohydrate reserves. A higher cut will also help to keep out invading weeds.

Most warm-season turfs do well with no fertilizer in the winter. However, Bermuda grass may benefit from one application of a slow-release nitrogen formulation in mid- to late-December. Apply at a rate of one pound of nitrogen per 1,000 square feet of lawn area and water in well. Be sure to uniformly distribute the fertilizer using a rotary spreader. If you do choose to feed the lawn at this time, a fertilizer high in iron (at least 2 percent) will help to green it up without adding to extra leaf growth.

Our winters are usually fairly rainy. But it is still important to make sure that the grass gets enough water. Irrigating twice weekly should be sufficient during winter dry periods. Early morning is the best time. Leave the sprinklers on long enough to apply about 600 gallons per 1,000 square feet of lawn with each watering.

Winter is when weeds become unruly. One application of a pre-emergent herbicide in December will help to prevent any new weeds growing from seed. Keep the grass cut higher on a regular basis to help control existing weeds. Use post-emergent herbicides, such as Weed B Gone, sparingly to control existing weeds.

Finally, this isn't the time to start a new lawn or renovate an old one. Wait until April and May. Don't scalp down the lawn now — wait for spring.

Jay Deputy is an education specialist in landscape horticulture and turf at the University of Hawai'i-Manoa, Department of Tropical Plant and Soil Sciences, and state administrator for the Certified Landscape Technician Program sponsored by the Landscape Industry Council of Hawaii. Got a lawncare or turf question? Write to deputy@hawaii.edu.