Oklahoma Gardens, Indian Summer to First Freeze!

Most of Oklahoma has now experienced their first light freeze and we have slipped into a pleasant round of Indian summer. Many of the more tender plants may have already frozen or they may have just been burned back. As we get colder in future freezes most plant material will call it curtains or make the conversion to compost material as they die from freezing. Some crops freeze at around 32° like sweet potatoes, others freeze at around 25°, and a few plants will survive down into the teens or single digits before shutting down. Annuals will be gone forever after they freeze unless it is a variety that leaves seeds behind that may sprout again next year. Perennials are crops that may freeze to the ground but the roots and crown will over winter and they will sprout out again next spring with new life. You can prolong the life of many of the less tender annuals and cool season plants with an occasional winter watering, especially before frosts or light freezes as a plant that is well watered will not dehydrate and freeze as easily. You can also cover plants for these early cold fronts with sheets, blankets, newspaper, cardboard boxes or commercial crop covers like Reemay fabric.

Oklahoma gardening is not over with a freeze. This is still a great time to plant trees and shrubs, the best time to plant spring flowering bulbs like tulips and daffodils and still a good time to plant pansies, ornamental kale and cabbage. You can also mulch your remaining plants to give them more protection, like a comforter, against the severe cold to come later this winter. The mulch will also hold moisture in the soil reducing the need for winter watering and the risk of plants getting winter leaf burn or dehydrating.

One of my favorite things is the chance to enjoy the natural show of fall colors as the leaves change on our deciduous trees and shrubs. The fall color is not only a spectacular show but it is also fun science to learn how the process works. It is a different show every year as a multitude of conditions are involved to determine how and when the leaves color and “fall” from the tree each autumn. The shorter day length is very consistent from year to year as one of the main triggers. But the day and night temperatures, timing of the first freeze, how hard the first freeze is, and moisture levels in the soil all vary from year to year. Like grapes for wine, fall color varies dramatically by year. The shorter day length turns a natural switch to tell the trees to start preparing for winter. With the shorter days and less intense sunlight the trees and shrubs turn down and then turn off the photosynthesis process that makes food for the plant. As the green chlorophyll used in photosynthesis disappears from the leaves we begin to see the yellow color of xanthophylls, the red and purple colors of anthocyanins or the orange color from carotenoids. These other pigments are allowed to put on their own show after the green chlorophyll is gone from the leaf party. In some of the most colorful trees, glucose is trapped in the leaves which turn the glucose a red color. This magical combination of factors produces a different but similar show of color every fall as our trees convert from making food and growing, to storing food. Make sure to spend some time driving and hiking to enjoy the show or you will have to wait another year to see what the show next autumn looks like.

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