A tropical plant that originated in Mexico, the poinsettia is very susceptible to chilling temperatures. If you purchase your plant on a cold day, wrap it completely before moving it from the store to your car. Place it in a sleeve stapled at the top to prevent rapid heat loss and to keep cold air from blowing onto the plant. As soon as you start the car, turn on the heat to a comfortable temperature.

At a winter Saturday morning farmers market on Riva Road, a shopper approached me with a Christmas wreath problem. In a week on her door, a wreath she had purchased at a local big-box store was turning gray-green, and its needles felt dry.     I was not surprised.

In June 2007, I wrote a Bay Gardener column about restoring a 1949 John Deere B tractor. A Bay Weekly reader called to offer me an old tractor, which had belonged to his father-in-law.     When I visited, I found a neglected Allis-Chalmers B parked at the edge of a woods. It had not been operated for at least 10 years. It would no doubt be a real challenge to restore to operating condition.

Short-day onions generate their bulbs when daylight hours are less than 12. If you are going to plant onion plants this fall, make certain that you purchase only short-day varieties. Short-day varieties can be successfully transplanted as late as mid-December and still produce a normal crop.     Many of us will be planting almost that late, as Dixon Dale onion farm, one of the nation’s largest producers of onion plants, did not have plants ready to ship until mid-November.

This year, our garden will be providing butternut squash, onions, garlic, broccoli, Brussels sprouts, carrots and red and green peppers for the Thanksgiving table. We might include sauerkraut that was made and canned in 2010. If needed we could also include Siberian kale and collard greens, but I prefer roasted Brussels sprouts.

A number of insects feed unnoticed on houseplants until perplexing changes alert you. Yellowing leaves are often seen as an indication that the plant is hungry and needs a dose of fertilizer. Yellowing leaves can also mean soft-shell scale insects are feeding on your rubber tree, crotons, philodendrons or related foliage plants. In sufficient numbers, these insects can cause leaves to turn yellow and appear deficient in nutrients.     Look for scale insects on stems, veins in leaves and leaf tissues between the veins.

One of the problems of moving houseplants outdoors during the summer months is that they often become infested with insects. You’ll want to control those bugs before bringing your plants back indoors.     A Bay Weekly reader sent me a sample of Christmas cactus that had been outdoors along with her other houseplants. She wrote that the plant had not been growing and, despite her care, continues to decline. On the five-inch-long piece of stem in the envelope, I counted 12 scale insects.

A Bay Weekly reader asked if I had seen an odd-looking pine tree growing on the west side of Rt. 4 about a quarter-mile south of the Patuxent River Bridge.     It’s a witches broom, and I have been admiring it for at least 10 years. The tree is some 20 feet tall and grows on the edge of the woods about 100 feet from the side of the road.

The editor of Bay Weekly recently asked if she could simply add potting soil to raise the level of rooting medium in her houseplants or if she had to repot. I advised her to repot.

I heard a garden advisor on radio tell his listeners to compost their leaves in plastic bags rather than placing them on the curb for pick-up by the municipality. Put the leaves in the plastic bag and dump in a pitcher of warm water with two to three packages of bakers yeast dissolved in the liquid, he advised.     I hope no one listened.     Composting is an aerobic process. The organisms involved are bacteria, fungi and actinomycetes. There are no yeasts in the composting process.