Window boxes have to be bold and brassy – I’m sorry to tell you this.

Yes, New Englanders are supposed to be refined and elegant, traditional and understated, and that works well with clothing, house decorations, hairstyles and even some large-scale gardens.

But a window box is a small container that you put below a window on the side of your house, designed to attract the attention of people driving by your house who can be as much as 50 feet away.

To get attention you need a 40-miles-an-hour plant – something that is such a striking color, so different from what is normal in that environment that you would notice it driving by, even speedily.

But before we start planting, let’s discuss the box.

It can be made from wood, plastic, metal, coir or just about anything else that will hold potting mix and stand up to sun, wind, rain and accidental jabs from painters and people mowing the lawn. It should have drain holes, so the plants won’t drown if it rains too much. And it should come within a couple of inches of matching the width of the window. Too long or too short looks weird.

Some window boxes are permanently attached to a house. In others, a holder is attached to the house and you remove the container for planting – which I think is easier – and you put the window box back on the house after you’ve worked your magic in planting it.

Use soil-less potting mixture such as Pro-Mix in the box. Potting mixture weighs less than garden soil, which means it will be a lot easier to lift up into position along the side of your home and will cause less stress on the screws, bolts or whatever holds the box in position.

Also the mixture holds onto moisture longer, and garden soil may have diseases or seeds that you don’t want.

You can re-use the potting mixture year after year, although it’s better to store it inside or under cover from December through April in Maine. Just be sure to fertilize every year with a time-release fertilizer.

The first plant decision is whether you will make just one planting a year in the box or switch it out. If you are eager to start the growing season, plant pansies in early April so you have something to look at until you put in the warm-weather plants in late May or June.

Or you might put bulbs in the box in your garage over the winter. Put the box on your house and put in a few pansies and violas with the tulips and daffodils as they come into bloom and your box will look like spring for six weeks.

For the main show, from June through the first frost, you need annuals. Since these plants die at the end of the year, they don’t have to store energy to survive the winter. They put all their energy into flowers or, in some cases, colorful leaves. Some perennials, especially grasses, also work.

This is trite but it works: You need thrillers, fillers and spillers. Thrillers are tall, striking plants. Spillers drape over the sides of the window box. Fillers cover the middle.

Figure out whether your window box is going to be in a sunny or shady location. If the box is on the north side of the home or under trees, you want plants that thrive in shade. For the east, south and west sides, with no trees, sun-loving plants will work.

Starting with sun, some of the best thrillers are grasses. Hakone grass is a great choice, about a foot tall, with yellow- and green-striped blades. Purple fountain grass and papyrus are also good choices. Geraniums can be either thrillers or fillers.

Remember geraniums come in other colors than red, and some geraniums have variegated leaves. Plus there are trailing geraniums that combine thriller and spiller functions. Celosia is a striking, bright annual in orange, pink or red.

For fillers think about color. Some varieties of coleus stand both sun and shade, so check the label. These plants get their color from foliage, not flowers. But many of the standard annuals work, including gazania, gerbera daisy, petunia, salvia, lobelia and zinnia.

Sweet potato vine is one of my favorite spillers, coming in dark purple or bright green/chartreuse foliage as well as other colors. Lysimachia has both attractive foliage and flowers. Lobelia is the classic, with its wonderful blue trailing flowers; there is also a white version. Verbena is another good one.

One spiller my wife Nancy likes is a perennial: lamium, which works in sun or shade. It has variegated leaves and is used in gardens for ground cover. The blooms can be white, pink or lavender. When the gardening season ends, she removes the lamium from the window box and plants it in our gardens.

For shade, the choices are more limited – especially for the taller plants. Some varieties of caladium and coleus get tall, and the foliage in both is multicolored and striking. Fuchsia is a bright flowering plant with unusually shaped blooms.

For shady fillers think about begonias first. We use Non-Stop begonias a lot, but rex begonias will also work. The blooms aren’t much, but the leaf colors are wild, everything from burgundy to many shades of green.

Pass by impatiens with the impatiens downy mildew, but the New Guinea impatiens are even more striking. Euphorbia “Diamond Frost” is a combo spiller/filler with a bushy cloud of white throughout the growing season.

For your spillers, decide what color you want and browse the aisles of the greenhouse. Bidens and calibrachoas grow in almost every color.

The beauty of shopping for annuals is that they will be in bloom when you get to your garden center.

Find some plants that you like, read the label to see if they like sun or shade, and take them home.

And then pat yourself on the back when passing motorists slow down for a long, admiring look.

Tom Atwell has been writing the Maine Gardener column since 2004. He is a freelance writer gardening in Cape Elizabeth and can be contacted at 767-2297 or at tomatwell@me.com.