How to Plant Flowers in Large Planters: Think Big With These 7 Tips

Mariel Loveland
Written by Mariel Loveland
Updated February 9, 2022
Couple planting flowers in a big planter
Photo: Sarah Mason / DigitalVision / Getty Images

If you want a super lush container garden, go big or go home

Anyone with a houseplant on their windowsill is already familiar with container gardening—but the bigger the planter, the more things to consider. Large planters are a blank canvas with a lot of space to fill. While it’s not the same as repotting your nearly indestructible six-inch pothos or another hard-to-kill houseplant. It's not exactly hard to create an impressive arrangement as long as you know the basics. Here’s how to plant flowers in large planters.

1. Pick a Planter With a Drainage Hole

Unlike the dirt outside, garden pots are easily waterlogged. If you’re using a non-porous planter like plastic or glazed ceramic, it can take weeks for excess water to evaporate. Too much water is a recipe for fungus and root rot. For this reason, you need a planter with a drainage hole.

If your favorite large planter doesn’t already have a hole, you can pick up a new one at your local nursery or drill your own. For a plastic planter, use a regular drill bit. For a ceramic planter, use a carbide-tipped drill bit.

2. Lighten Your Planter’s Load With a Pot Filler

The problem with large planters is that they’re heavy. If you fill them up completely with soil, it might be hard to store your flowerpot for the winter. For this reason, you should add a lightweight filler at the bottom of your planter. Raid your recycling bin and opt for lightweight plastics that won’t get waterlogged or break down. This could include:

  • Plastic products like milk jugs or soda bottles

  • Styrofoam blocks

  • Plastic flower pots turned upside down

  • Packing peanuts (as long as they’re not the kind that dissolves when wet)

  • Crumpled plastic bags from the grocery store

Out of all of these options, rigid plastics tend to perform the best. They provide air pockets that promote healthy root growth and stave off root rot.

3. Choose the Best Growing Medium

Closeup of a woman holding soil in her hands
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If you want to grow healthy garden plants inside a large planter, you shouldn’t use pure garden soil (which compacts too easily) or topsoil (which often lacks the nutrients needed for potted plants). Instead, reach for potting soil or potting mix. People often use these terms interchangeably, but they’re slightly different.

Whichever you choose, the ingredients matter. Since the growing medium varies by brand, look for additives like pearlite, vermiculite, peat moss, ground pine bark, and coconut coir. These help retain moisture and nutrients, aerate the soil, and anchor your plant.

4. Don’t Be Afraid to Think Beyond All-Purpose Potting Soil

The ideal potting soil or mix for a large planter is light, fluffy, and moist without being waterlogged—but there are so many different types. Use the wrong one in your window box or flower pot? Your plant will probably survive, but it won’t thrive. So, how do you choose?

All-purpose potting soil is a great place to start, but it’s not always the best choice. Depending on what’s going in your planter, you may also want to consider:

  • Indoor potting mix: a soilless mixture that’s sterile and has better aeration for indoor container gardening

  • Cactus and succulent mix: a good option for desert plants that need extra sand and increased drainage

  • African violet mix: a good option for tropical plants that need aeration and high moisture

  • Orchid mix: a must-have mix for orchids that mimics their natural habitat (since they’re epiphytes, they grow on other plants)

  • Seed starting mix: if you’re growing your flowers from seeds, start with a seed mix

Once you choose your soil, fill your planter two-thirds of the way.

5. Finesse Your Mix With Fertilizer

Want really lush flowers? It’s time to finesse your soil with some extras. If your mix doesn’t already come with starter fertilizer, choose a slow-release fertilizer. These come in stick or pellet form and generally release over 60 to 120 days. You can supplement this type of fertilizer with a water-soluble (or liquid) fertilizer as your flowers begin to grow. Look for a liquid fertilizer with equal parts nitrogen, phosphorus, and potassium.

6. Choose a Thriller, Filler, and Spiller

large wooden planter with different kinds of flowers
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Once you’ve prepped your soil, it’s time to plant your flowers. The best options depend on your USDA Zone. If you’re not sure, hire a local gardener to help you plan your space. Regardless, you should layer three different types of plants for a high-impact arrangement.

Thriller Plants

Plant a thriller in the center of your pot. This serves as the focal point of your planter. It should have big colorful blooms or large decorative vegetation (think: Tuscan Sun perennial sunflowers, Endless Summer hydrangeas, or Tropicanna Cannas).

Filler Plants

Use this type of plant to fill in the space around your thriller. Reach for plants with delicate leaves or flowers with smaller blooms (like Zinnias or Perennial Salvias). Always keep your color palette in mind. Fillers should compliment thrillers.

Spiller Plants

Choose a spiller plant that hangs over the edge of your large planter and makes your arrangement look extra lush. This is especially important if you have a tall or raised planter. Reach for trailing plants like verbena, sweet potato vine, trailing snapdragon, and ivy geranium.

7. Keep the Tags

Once you've planted your flowers, give them a healthy dose of water and save the tags. The tags that come inside your nursery pots will help you identify your flowers as they grow. They’ll also give you crucial care advice, like light and watering requirements and other information that can help you prepare your flowers for winter down the line.