First cool weather of the season

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Recent cool weather and the temperatures especially at night are beginning to trigger changes in our home landscape and vegetable gardens.

There has been a little bit of fall color beginning on some shade trees, mostly red maple cultivars and some on burning bush. It will be our cool nights and warm daytime temperatures that really kick in the strong colors as pigment content in the leaves start to change from the greens to the reds, oranges and yellows. Sometimes early fall color can signal a problem with plants too. It won't be from being too dry this summer that is for sure. Trees and shrubs that have been planted this season can show that early color, but because they have been transplanted and not because there is a problem. Those limited and not yet established root systems are the typical cause of that color. Gardeners need to remember that it will take one year of recovery for every inch of tree trunk diameter before we consider the tree over transplant shock. The same rule of thumb applies to evergreens too! As our fall weather triggers the storage of food reserves in the roots, it is a great time to plant trees and shrubs.

Not wanting to leave out our needled and broad leaved evergreens here, they too are changing, just harder to see. First they will remain green throughout the winter, using up available soil moisture and moisture within the needles and leaves. You should not expect to see any major color change on needled evergreens besides the annual needle loss of some interior needles. Broad leaved shrubs may change color for the winter and some interior leaves may decline with a yellow color first, and later brown. Needle and broad leaved evergreens will greatly benefit from a late and even later watering. Before you roll up the hose for the winter in November, water them one more time.

In the vegetable garden our warm season crops like tomatoes and peppers will be impacted much more so than our cool season vegetables like those in the cabbage family. The ripening process with warm season vegetables will slow down, so tomatoes will still ripen, but just take a bit longer. Cabbage, Broccoli, Swiss Chard, Fall and winter radishes will really enjoy the cooler nighttime temperatures and not be bothered by the lower daytime temperatures either. There is even time left to sow more of the leaf lettuces and harvest them as baby or micro greens.

Perennial flower beds will be changing as well. Where those pollinated flower heads have been left, seeds are filing out to be eaten by birds. Examples are sunflowers and coneflowers. Those seeds that escape being eaten will likely show up as volunteers next year, perhaps where you want them, but often times that is not the case. The good strong foliage color will be fading a bit as perennials will also be moving food reserves down into the root system just like the other plants in the landscape. Cleanup of those beds should wait until they have naturally died down if you can.

About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.