In the next couple of weeks temperatures should drop, signifying the beginning of our very short winter. The average first frost date in the Fresno/Clovis area is (or once was) Nov. 15. Our winters during these last drought years have been even shorter and warmer, with only a brief spell or two of freezing temperatures around the time of the winter holidays.
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The first frost (32 degrees) can act as a trigger for plants to enter winter dormancy after a growth spurt during several weeks of our mild early fall temperatures. It doesn’t usually cause significant damage to plant tissue on most plant species, but may knock down the foliage on subtropical plants including bougainvillea, bananas and cannas.
The root systems on subtropical plants will remain viable. Protecting the root systems on subtropicals from freezing temperatures will help them recover more quickly next spring. Fallen leaves and dead foliage can provide some insulation from the cold, but laying down some sort of cloth tarp, old blankets or towels over the root systems on nights when frost is predicted will maintain higher soil temperatures. Remove the tarps during the day and let them air dry.
Move frost-tender potted plants to a spot near a south- or west-facing wall that will retain and reflect heat from the sun onto the plants on frosty nights. Covered patios, arbors, overhanging eaves and large tree canopies will offer some protection for container plants from light frosts.
Citrus trees are also subtropical plants and will suffer branch and twig dieback and leaf loss after a hard freeze (at or below 28 degrees for a minimum of four hours), but mature citrus with a full canopy of leaves can tolerate light frosts fairly well.
Hard freezes are most common in the last weeks of December and early January, but just in case of an early hard freeze, keep cloth tarps or blankets handy to cover the tree. Cover young citrus with tarps whenever temperatures drop below 32 degrees. Outdoor UL-approved lights hung in the interior branches will create a warmer microclimate. Keep a few strings of lights handy as well.
If you’re hoping to extend the harvest season of tomato and pepper plants with fruit still ripening, try using row covers, water walls or cloches to create and maintain warmer temperatures. Cool-season crops including broccoli, kale and peas, as well as root vegetables like radishes and beets, will stop growing when nighttime temps drop to near freezing. A really hard freeze will damage winter crops. Use row covers to protect them on mid-winter nights when skies are clear and the stars are shining brightly.
Wet soil stays warmer than dry soil, so deep irrigate citrus and planting beds during the day before freezing nights. Container plants will need weekly watering (abide by your municipal rules) to keep the soil moist and create that important warmer microclimate. But remember to cut back on irrigation times for lawns and planting beds and to turn off irrigation systems when it’s raining.
Deciduous mature landscape trees will be entering dormancy this month. Continue to deep irrigate them monthly this fall until the winter rains arrive. Most of our rain falls in late winter and early spring. If amounts are once again well below average (11.6 inches), continue to deep irrigate large trees monthly all year long.