While a single plant in a single container is a natural, and often dramatic, way to go, consider mixing plants. A tall specimen surrounded by smaller plantings, whether a carpet of the same plant or a mix of coordinating plants, can give a container a more polished appearance. Or think of starting with a tall accent plant, adding filler plants around it, and then planting spillers (plants that grow downward) around the edges. Play with plant and color combinations at the nursery or garden center to see what appeals to you.

Choose a container that is the right size for your plantings. You want one large enough to allow the roots to spread and the plant or plants to grow, but not so large that greenery is swallowed up by it. Keep in mind the eventual plant size, especially if it’s a permanent planting such as a large shrub or tree. In that case, it’s fine to have the plant look a little small at first rather than have it outgrow its container.

Before planting, add a small square of window screening over each drain opening to keep the soil in place while allowing the water to drain. Traditionally, potshards—pieces of broken pots—have been used by container gardeners, but these can actually hinder drainage.

If you want to add polymers, which are crystals that help retain moisture, prepare them according to the package directions and combine them thoroughly with your potting mix. Whether you add polymers or not, add water until the soil is slightly damp, enough to hold together but not soaking wet.

Add the potting mix to the container, filling it to a height where the top of the rootball of the largest plant will sit 2 inches below the rim of the pot. Firm it in place. Loosen the roots of the largest plant and set it in the container. If the plant has long roots, you may need to create a trench to allow the roots to grow down into the soil. Use additional potting mix to hold the plant in place.

Add any additional plants; the top of each rootball should be 2 inches below the rim of the pot. You may need to add soil beneath smaller plants. Once the plant or plants are in place, fill in with potting soil, firming it as you go. Water gently but thoroughly.