Things a gardener should know to prepare for those holiday after-dinner discussions

I’ve been stuffing little notes into my pockets the past several weeks.

They’re filled with facts of the winter season – things a gardener should know to be fully prepared for those holiday after-dinner discussions.

Check ‘em out and see how you score.

• All poinsettia flowers are yellow. That’s true. The bright reds, pinks and whites come from floral bracts – modified leaves. If you look at them closely you’ll see that the first leaves to show color look much like the green leaves. Gradually their shapes change as new leaves are produced, and then, as the heads reach their full color, the pea-sized true flowers (always bright yellow) emerge in the centers of each head. Poinsettias are true euphorbias, and those flowers are characteristic of the entire genus.

And while we’re in the world of poinsettias, they are not poisonous. That’s an old tale that’s been told and retold, but research conducted at Ohio State University in 1974 showed that they aren’t poisonous to humans. Irritating to the eyes and maybe the skin, yes, but definitely not poisonous. However, mistletoe berries, holly berries, tulip and daffodil bulbs and azaleas are toxic, so don’t include those in your holiday dining.

• Killing frosts can occur at temperatures above 32F. Frost can form on surfaces like windshields, blades of grass and flowers and leaves of tender annuals and tropicals at temperatures several degrees above actual freezing (32F). But it has to be clear and calm, not cloudy or windy. If you have tender plants, and if temperatures are going to fall to 35F, 36F or even 38F, you might see frost patterns and damage the following morning. Be forewarned and be prepared to take action to move plants into protection or cover them with frost cloth when needed.

Just because a plant is listed as “hardy” to your locale doesn’t always mean it will survive a winter cold snap. We saw that last February. There is a big difference between “hardy” and “hardened.” The United States Department of Agriculture has, for 90 years, kept detailed records of the lowest temperature reached in each city or county in America each winter. Those temperatures have been averaged and the USDA Plant Hardiness Zone Map was created in 5- and 10-degree increments. You can find that map online and in many gardening reference books.

All species of landscape plants are then plotted against that map to determine where they can reasonably be expected to survive average winters. Plants are listed as “hardy” to those “Hardiness Zones.” Following 15 years of warm winters early this century, DFW got reclassified into Zone 8 in the latest (2012) map, but many of us still consider us to be in the colder Zone 7.

However, a plant must be properly “hardened” to cold to survive normal low temperatures in its Zone. If it has become acclimated to warmer weather and then faces a strong cold front, severe damage or even plant loss can occur. That’s what happened last February, and that’s why we lost so many plants that normally would have survived here. Compounding the problem was the depth of the low temperature and the length of time that it stayed cold in February.

• Spring-flowering shrubs and vines must not be pruned in the winter. This is the time during which they are setting flower buds so they can bloom as soon as the weather turns warm. Pruning them now (during the winter) would trim off most, if not all, of those buds. Those plants must be pruned immediately after they finish blooming in spring.

The exception would be peaches and plums, since we do drastic pruning to keep the trees growing horizontally and to limit the number of fruit their limbs have to carry. Those trees do get pruned in the winter. Blackberry canes are pruned after they bear fruit in late May or June. Old canes are cut to the ground, and the current year’s canes are left to bear fruit the following spring.

• Mulches don’t “keep plants from freezing.” They moderate the rates of freezing and thawing. Your goal in pulling mulches up around perennials and annuals isn’t usually to keep the plants from freezing, but more to keep them from freezing and thawing rapidly and repeatedly. In human terms, it’s similar to our bodies suffering from frostbite. Doctors want us to run cool water over frozen flesh so it doesn’t warm up too quickly.

Of course, mulches bring other benefits with them. They cut back on evaporation due to soil’s exposure to air. They make it much harder for weed seeds to germinate, and they slow or prevent erosion by letting water soak deeply into the ground.

You can hear Neil Sperry on KLIF 570AM on Saturday afternoons 1-3 pm and on WBAP 820AM Sunday mornings 8-10 am. Join him at www.neilsperry.com and follow him on Facebook.

This story was originally published December 3, 2021 at 5:45 AM.