We took our annual Thanksgiving Day long walk this year wearing shorts, T-shirts, sandals and mosquito repellent. Very warm weather for the end of November. So warm that many plants were way off schedule. Dead and new hydrangea flowers on the same bush; spring-blooming bulb foliage up already; roses in full bloom with perfect buds and flowers and vigorous new growth; camellias and azaleas flowering in late fall.
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Our coldest temperatures of the year usually occur during the winter holiday season. If we have several nights in succession of below freezing temperatures in the next few weeks we can expect to see severe freeze damage on out-of-season tender new growth and flowers. The freeze damage can also extend into canes and branches.
Forcing flowering and budding plants to enter into winter dormancy and protecting their still-active roots can help them survive freezing temperatures with less damage and reset their bloom timers back to early spring.
One trick that works well for increasing chill hours for lilacs in order to encourage them to set spring flowers is to dump ice on the roots in winter. Pouring ice over early sprouting spring bulb foliage and camellias and azaleas may slow down flower production timing. A very early spring fertilization of leaf tips with bulb food or bone meal when they normally first appear is the usual recommendation, but feeding now would be premature. Wait to fertilize spring-blooming bulbs and other spring flowering plants until spring.
Remove all hydrangea flowers and cut back a third of the older, grayer or broken branches to the ground. Cut back remaining canes by a third to just above a double-leafed node if possible. This pruning technique will guarantee summer flowers since most hydrangea varieties bloom on old wood, although some newer hybrids bloom on old and new wood.
Roses will continue to flower and set new buds during our short, mild winter unless we trick them into dormancy by removing all green growth. Make your last bouquet of the season this week and then cut off all spent flowers, buds and new growth. Pre-prune roses by also cutting off any weak, spindly growth and any canes that cross through the interior. Then strip off all the green leaves. It’s a bit easier and faster to blast most of the leaves off with water from the hose rather than hand stripping.
A light freeze (32 degrees or below) will kill summer-blooming vincas and impatiens and tender herbs including basil and tarragon, but a hard freeze (28 degrees or below) can damage but not kill wax begonias and subtropical plants such as banana, canna lilies and bird of paradise. Leave ugly brown or gooey freeze-damaged leaves on as long as you can stand the sight of them; the dead leaves will provide some further frost protection.
One of the many benefits of mulches is that they act as an insulating blanket over roots, moderating soil temperature fluctuations. To help prevent roots from freezing temperatures, maintain a 3- to 4-inch layer of mulch around all plants, especially those that have bloomed late or early and not yet begun to enter winter dormancy.
Send Elinor Teague plant questions at firstname.lastname@example.org.