A customer pulls a wagon full of plants up to the cash registers at Skillins Greenhouses in this archive photo. Fall can be an excellent time to plant, in part because nurseries typically put any plants they haven’t sold over the spring or summer on sale. Brianna Soukup/Staff Photographer

It is, as of today, autumn for everyone, both traditionalists like me, who believe the seasons are ruled by the sun, as well as TV weather people who for some reason have decided that autumn starts on Sept. 1.

Many people believe that gardening is for spring and summer, and fall is for the harvest, cleaning up and getting ready for the cold, snowy weather. Actually, you can plant in late September, October and even into November, if the ground isn’t frozen or snow-covered, and there are good reasons to. And I don’t mean bulbs, either – the daffodils, tulips, allium, hyacinths, garlic and similar plants planted in the fall that bring color, aroma, flavor and joy in early spring.

Price is the main reason to buy trees and shrubs now — and by the way, deciduous ones work best. Local nurseries don’t want to store plants all winter. They can’t be left outside in pots because the soil and roots would freeze hard, injuring, if not killing, the plants. But moving the plants into greenhouses would take a lot of labor, and then the nursery would be stuck tending them all winter. Instead, come fall, nurseries dramatically lower their prices, often by a third. Thrifty Mainers like this, but that is just one reason to plant in the fall.

While air temperatures have cooled, the soil still retains much of the summer’s warmth. The plant’s roots like this so they will grow a little, settle in and be poised to burst into life in the spring. They’ll have a jump on trees or shrubs you plant next spring.

Most years, we get a lot of rain at this time of year, which also helps the new plant settle in. (As I am writing this, though, in mid-September, that rain has been largely absent.) Either way, you do have to water generously when you plant. Dig a hole twice the size of the pot or root ball. Fill that hole with water and let it drain. Fill it again and put in the plant. Let it drain again, add soil to fill the hole, and again, water heavily.

Without heavy rain, you will have to water your newly planted trees and shrubs regularly, though, because it’s cooler now, not quite as often as you did after spring planting.

Hardy perennials can also be planted in the fall, and their prices will also have dropped. It probably makes sense not to push the zones on perennials, maybe using one zone hardier than the one where you live. If you are Zone 5, do fall planting with plants that are Zone 4 or hardier. And it’s best to stop planting perennials by mid-October.

Potted perennials that can be planted now include Black-eyed Susan (Rudbeckia), garden phlox, German bearded iris, globe thistle, bee balm, catmint and day lilies. Many potted perennials have been in those pots for months so the plant roots may fill the pot, growing in circles. For future good growth, cut the roots. I usually cut them in four, quarter spots around the root ball and tug the quarters apart as much as I can before planting them.

A few plants, such as Nigella and Calendula, will sprout in the spring from seeds you plant now. Nigella, commonly called “Love in the Mist,” is a hardy annual with blue, white or pink flowers. The blossoms are surrounded by fine-leaved foliage, which give them an interesting look. Calendula, which is actually an herb, also self seeds if not dead-headed.

These Flanders Field poppies in columnist Tom Atwell’s garden self seed. But you could buy the seeds now, and spread them in your garden. Photo by Tom Atwell

Any plants that self-seed in your garden also can be planted from seed in the fall. We’ve had most success with the Flanders Field poppy, which is the one handed out – well, paper replicas are – on Veterans Day. These self-seed in our vegetable garden: The seeds form and drop in summer, hang around in the soil under the snow and sprout in the spring. To introduce these poppies to your garden, buy seeds and spread them this fall.

Morning glories, a vining annual flower, works the same way. We grow them on a trellis in front of our heat pump, where none have self-seeded. But next to our shed, our morning glories regularly drop seeds that sprout and grow in the spring.

All of this serves as a reminder that gardening season isn’t over.

Tom Atwell is a freelance writer gardening in Cape Elizabeth. He can be contacted at: tomatwell@me.com.