How to Plant a Flower Container Step by Step

An empty pot, a bag of potting mix and a tray of young plants: that is everything you need to plant a flower container that looks full and balanced within a few weeks.

What makes the difference is the order you do things in and a simple way of choosing plants so that the pot has height, body and something tumbling over the edge. The steps below take you from the bare pot to the first watering.

The Recipe: Thriller, Filler, Spiller

A well-known design aid divides container plants into three jobs:

• Thriller: one tall focal plant that gives the pot height, such as an upright grass, a spiky flower or a tall geranium.
• Fillers: mounding plants that surround the thriller and cover the mix, such as petunias, marigolds, begonias or coleus.
• Spillers: trailing plants set at the rim to soften the edge, such as verbena, sweet alyssum, lobelia or sweet potato vine.

It is a guide, not a law. The one rule that does matter is that every plant in the container shares the same light and water needs, because they will all get the same of both. For plants sorted by light, see the sun and shade choices for containers, and for choosing colors that sit well together, see the guide to flower garden color schemes.

Choose the Pot and Gather Supplies

Pick a container with at least one drainage hole and enough volume for the roots of several plants. A pot roughly 14 to 18 in (35 to 45 cm) across comfortably holds a thriller, three or four fillers and two or three spillers, though the right number depends on how large each plant grows. If you are still deciding on size and material, the beginner guide to growing flowers in containers compares the options.

You will also need fresh potting mix (not garden soil), a trowel or scoop, water, and a small piece of mesh or a curved pot shard. Water the plants in their nursery pots an hour or so beforehand; moist root balls slide out cleanly and settle in faster.

Plant the Container Step by Step

1. Put the pot where it will live. A large container full of wet mix is heavy.
2. Cover the hole, but skip the gravel. Lay the mesh or shard over the drainage hole only to keep mix from washing out. A layer of gravel at the bottom is not needed; it does not help drainage and it takes room from the roots.
3. Moisten the mix. Dry potting mix sheds water at first. Tip some into a tub, add water and stir until it feels like a wrung-out sponge.
4. Fill the pot. Add mix to a few inches below the rim, leaving room for the root balls. Do not pack it down.
5. Test the layout. Stand the plants, still in their nursery pots, on the surface. Shift them until the arrangement looks balanced from where you will usually see it.
6. Plant the tallest first. Set the thriller in the center if the pot will be seen from all sides, or toward the back if it stands against a wall.
7. Add the fillers. Slide each plant out, gently loosen any roots circling the root ball, and set them around the thriller.
8. Finish with the spillers. Place them at the rim and tilt them slightly outward so the stems head over the edge from the start.
9. Level and firm. The top of every root ball should sit level with the others and about an inch (2.5 cm) below the rim. Fill the gaps with mix and press lightly with your fingers so there are no hollow pockets. Do not bury the crown of any plant.
10. Water until it drains. Water slowly over the whole surface until it runs from the hole. If the mix settles and exposes roots, top it up.

Why the Gap Below the Rim Matters

That inch of space is your watering reservoir. If the mix reaches the top of the pot, water runs off the sides before it can soak in, and the center of the root ball stays dry. If the mix sits much lower than that, the plants are shaded by the rim and the pot holds less than it could.

How Close to Plant

Containers are planted more closely than beds. In the ground, spacing allows for the size a plant reaches over a whole season or several years. A seasonal container is meant to look full quickly and is emptied when the season ends, so the plants can nearly touch at planting time.

There is still a limit. Leave a little mix between root balls so each has somewhere to root into, and resist squeezing in one more plant. An overstuffed pot dries out very fast and air moves poorly through the leaves.

Care After Planting

A few small habits keep the new container going:

• Check the mix before watering. Feel about an inch down. Water thoroughly when it is dry at that depth and wait when it is still moist. Need rises as plants grow and the weather warms.
• Feed according to the label. Potting mix runs low on nutrients as the season goes on. Use a fertilizer made for flowering container plants and follow its directions.
• Deadhead. Remove faded flowers from plants that benefit from it, such as geraniums, marigolds and many petunias.
• Trim the trailers. When spillers grow long and bare near the top, cut them back by a third or so to prompt fresh growth.

Refreshing the Pot as Seasons Change

A container does not have to be finished the day you plant it. When one plant tires, lift it out with a trowel, add a handful of fresh mix and tuck in a replacement with the same light needs.

The same idea works across the year. Cool-season flowers that fade as summer heat arrives can make way for heat lovers, and those can be swapped for cool-season plants again when temperatures drop. In mild-winter climates, that cool-season planting may be the longest display of the year; in cold-winter regions, the first fall frost usually ends the show for tender plants.