Make Spring Happen in Your Window Box

A picture of annuals in a container planting.

No matter what the weather brings, we can get a little spring fix with our own windowbox and porch pot displays. Spring annuals are charming, frivolous, fragrant and colorful, and really worth it.

By Steffie Littlefield

This article was first published in The Gateway Gardener March 2018 issue.]

No matter what the weather brings, we can get a little spring fix with our own windowbox and porch pot displays. Spring annuals are charming, frivolous, fragrant and colorful, and really worth it. The design of a good window box planting is critical to its success and longevity, but is not hard, it just takes planning. Plants that grow to the proper portions, require similar conditions of sun and moisture, adequate numbers of plants to start with, the best planting soil, a water source and slow-release fertilizers must all be taken into consideration. Like any good recipe, don’t skimp on the ingredients or your soufflé may fall flat…

A few notes about the structure of your window box. Make sure it can withstand being wet for extended lengths of time, does not rot or rust too easily and is secure enough to the windowsill or wall to hold quite a bit of weight from wet soil and growing plants. Now please use fresh potting soil each year and include a slow-release fertilizer that will continue to feed your plants when you are on vacation in the summer. Also arrange for adequate water supply from a drip irrigation system or from a scheduled routine including you and your neighbor while you are out of town. Please water your box as soon as you finish planting and every day while it is getting established!

My favorite part is the plants and their arrangement. I love the old-fashioned spring annuals that shout “Spring is Here”. These include snapdragons, alyssum, dianthus, linaria, lobelia, stock, nemesia, ranunculus and the queen of spring, pansies. The list can go for pages since I seem to love all flowering plants, but the point here is to find a combination of florific plants that have colors that blend and contrast well and are bright enough to stand out from a distance or even from 8-10’ below. I like to start with a neat row of upright flowering plants like snapdragons or stock in a scrumptious color and then pair that with some trailing plants with flowers or colorful foliage to highlight the taller plants color. Here is where you use the new trailing alyssum ‘snow princess’ or trailing pansies, lobelia, nemesia, or even add variegated ivy or golden creeping jenny. Good design dictates that you start with an odd number and fill in the spaces with an even number, but if you have a large planter or are running window boxes in a continuous row then just space your upright plants about 6-8 inches apart and fill in your box properly. Then select a bushier type plant to fill in around the other plants. Some of my favorites include elegant ranunculus, darling linaria, and sweet dianthus. For even added drama include some cut pussy willow or forsythia branches in the back or middle of the box. The height that is gained with these really sets your design off from a distance. Now you have to get brave and pack in the plants, because for a window box to really be memorable it must be filled to overflowing, to the point of being lavishly opulent. Yes, stuff those plants in if you want your neighbors to be jealous and the mail carrier to take a second look.

As your plants grow large and lush it is expected that you will trim them and shape them to encourage strong new growth as the season wears on. Deadheading flowers and trimming leggy vines just improves their vigor and stimulates new shoots to revive tired looking plants, keep the clippers handy. When the weather turns really warm thin out the waning flowers and slip in some heat tolerant zinnias, begonias, petunias and vinca to refresh your display.

Steffie Littlefield is a horticulturist and garden designer and part-owner of Edg-Clif Farms & Vineyard. She has degrees from St. Louis Community College Meramec and Southeast Missouri State, and is a member of Gateway Professional Horticultural Association and past president of the Horticulture Co-op of Metropolitan St. Louis.