1. Consider Container Size
No matter the size of your planter, the goal is to avoid overcrowding your plants to the point where they all don't grow well. But you also don't want a sparse-looking container garden. Here are some general guidelines, based on the diameter of your pot:
- 10-12 inch pot: Stick to 2-3 small plants or 1 medium plant.
- 14-16 inch pot: Ideal for 3-5 small to medium-sized plants.
- 18 inches and up: Larger pots can support 1 or 2 space-hungry vegetables, or mixed arrangements of smaller ornamental plants.
Avoid using a pot smaller than 10-12 inches outdoors, even to grow just one little plant. The soil in the pot will likely dry out so quickly it will be a challenge to keep up with watering enough.
2. Keep Your Plant’s Full Size in Mind
When starting out with small, young plants in your container, a common mistake is to pack in too many to fill the available space without thinking about how big they'll end up getting. For example, a little tomato seedling will quickly grow in all directions, smothering the basil plants you may have tucked in around it in your pot.
Instead, make sure to leave enough room to accommodate the mature size of your tomato variety, and any other type of plant you want to grow in the container. That may mean your container garden looks a little sparse at first, but it won't take long for your plants to start growing and looking lush. Always check plant tags, read seed packets, or do a little online research to find the full height and width of each type of plant you want to grow in a container so you can avoid overcrowding.
3. Layer Plants in Mixed Containers
When creating a decorative container of mixed plants, one strategy to maximize both the available space and the visual impact is to include “thrillers, fillers, and spillers.” These terms refer to the different types of growth habits that create layers of texture and color in your container garden.
- Thrillers: Taller, upright plants that are typically placed in the center or back of the container where it can fill vertical space. Some popular choices include ornamental grasses, salvias, angelonias, and coleus. Usually you just need one thriller per container.
- Fillers: Medium-sized, mounding plants that will add volume to the arrangement but won't get taller than the thriller plant. Marigolds, begonias, impatiens, and lobelia tend to work well. Aim for at least 3 fillers planted around or in front of your thriller (add more if your container allows room).
- Spillers: Trailing plants that form another layer to your arrangement as they grow over the sides of the pot. Examples include calibrachoa, sweet potato vine, bacopa, and licorice plant. Tuck them around the edge of your container, off-set between your fillers.
4. Go for Balance
Whether you're growing a mixed planter or a pot of herbs, the best number of plants for your container is a bit of a balancing act. When you get it right, all the practical needs of your plants are sufficiently met (sunlight, water, and nutrients), while the look of your container garden is neither overcrowded or sparse.
Because there is so much variability in the size, shape, and growing requirements of different plants, it often takes some experimentation to figure out what works best for the containers you have. Sometimes even if you follow all the planting "rules," you might not end up with a perfect balance. But then you'll know what tweaks to make for more success next time.
5. Make Adjustments as Needed
If your containers never quite fill in as much as you had envisioned, you can always tuck in another plant or two. And if you have the opposite problem of too much of a good thing, do some pruning to keep everything in bounds, or even remove entire plants so the rest of your plants have enough room to look their best.
