What to bring in, what to cover this fall

The average first frost at the Chicago Botanic Garden is Oct. 15, though it is typically later in Chicago. My sense is that first frosts are trending later now, so monitoring the weather is the best approach when making garden maintenance decisions affected by temperature.

Tender plants can be protected from light freezes by covering them with sheets, plastic or boxes. When night temperatures begin dropping below 40 degrees, it is time to bring in any tropical plants that you are keeping outside. A gradual decline in temperatures over a period of time is best, as the plants will acclimate some to the cooling weather. You may want to move tropical plants in for a night if there has been a long spell of warm weather and a sudden dramatic drop in temperature is predicted.

It’s OK to think about holiday lights now

Warm fall days are great for installing holiday lights, though most people do not think about installing lights until after Thanksgiving.

Our Chicago Botanic Garden staff starts installing strings of lights in early July. It is much easier to wrap branches with strings of lights on warm days in mid- to late October rather than on cold days in late November or early December.

Use LED lights to save on power so you will be able to use more strings on a circuit. Buy warm-color white LED lights if you want to match the color of commonly used white incandescent lights. Cool-color LED white lights have a blue cast to them.

Wrap branches of your trees with strings of lights to accent the tree’s form. You may be able to leave lights on your trees for a few years to save time. As the tree grows, the lights will tighten and will need to be reinstalled. Be sure to use power cords that are rated for outdoor use.

How to keep coleus

If you want to save your coleus for next year, this is a good time to take cuttings that are 4 to 6 inches long and root them. Put them in water, removing any lower leaves that will be in the water and pot them up once they form roots. Grow these plants outside until the temperatures begin dropping into the 40s. Keep them in a sunny window for the winter, pinching the plants back as needed. I have had good results holding coleus over winter; the plants do get a bit leggy as the light in my basement’s window is not at an optimum level.

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.