Answer: When you plant in a window box, there needs to be some balance between the space for the roots and the top size of the plant. If your box is narrow and shallow, you may not be able to grow something too awfully tall or large due to lack of soil volume. However some colorful fairly large growing plants that will grow well in large containers include sun coleus, Perilla Magilla, tropical hibiscus, lantana, mandevilla and thunbergia. The last two are vines and can be trained on a trellis to add height. All of these need full sun to grow well. Your local professionally trained nursery staff may have additional suggestions based on a more detailed understanding of the growing conditions in the window box you want to fill.
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