I don’t have boxes under the windows of my house, but I did plant two boxes that were on the front porch for the summer. I had two identical metal boxes, and two “vintage style” wire baskets that I thought worked well together. So I put the boxes on top of the turned-upside-down wire baskets. (Since the boxes only had two tiny drainage holes, I drilled four more and then used a wire through those holes to hold the boxes securely on top of the baskets.) Here is how they looked this summer:
I used the following Proven Winners plants on my porch this year: Senorita Blanca Cleome in the center of each box, and Vermillionaire cuphea on either side. In the front I put Mecardonia Gold Dust, Evolvulus Blue My Mind, and a Citrus Blend Lantana in the center. The Evolvulus and the Mecardonia did well but the Lantana was too shaded by the Cleome, which is a total over-achiever. Through September these boxes were beautiful, but I wanted to update them for fall without taking everything out. So I just removed the Cleome in the center. (Note: the coleus that’s in the blue pot on the side with some white New Guinea Impatiens is Sedona, one of my favorites. That pot needed shade-tolerant plants because the rose and honeysuckle on the porch post shield it from the sun.)
I left the Mecardonia and Cuphea. The Cuphea continues to attract hummingbirds as they migrate south, and I know from experience the Gold Dust Mecardonia will survive mild frosts. But I planted three ornamental cabbages in the center, along with a Snow Princess Lobularia. Snow Princess will continue to grow and bloom into December where I live, so it’s a far better fall annual than any chrysanthemum.
Once the Cleome was removed, however, the Cuphea became the tallest plants in the boxes. It’s not the best design to have tall plants on the ends of a long planting, instead of the middle: we want the tops of container plants to create a triangle that peaks somewhere near the middle. So to create that line I cut some bare branches from a shrub, stuck them near the Cupheas, and bent them over into an arch, tying the branches in place with twine.
Then I stuck some of the Cuphea stems into those branches. Now I had a taller center, and the branches framed the cabbages, Snow Princess and the collection of small pumpkins placed in the spaces. Notice in this photo how I used small clay flowerpots to hold some of the pumpkins a bit higher.
The front porch is “fallified!” After hard frost or as we pass Thanksgiving I’ll remove the small pumpkins (if the chipmunks or squirrels don’t do it for me first) and any wilted annuals, and stick some cut evergreen branches of assorted textures and some berried holly into the soil.
Other plants that work well for fall pots and boxes are ornamental kale, Heuchera and grasses. In general I avoid mums because the bloom time is so short.