Container gardening offers flexibility for decorating small or temporary spaces. Success depends on understanding that a container is fundamentally different from a garden bed. Plants in a confined space require specialized materials and planning to ensure root health and sustained vigor. A self-contained system needs components that specifically address drainage, nutrition, and structural support.
Selecting the Proper Growing Medium
The substrate that holds the plant roots is the most important component in any planter. Standard garden soil should be avoided entirely. Its fine particle structure is designed for open ground, not for a limited pot. When confined and repeatedly watered, garden soil compresses rapidly, reducing the air pockets necessary for roots to respire. This compaction leads to poor drainage, causing roots to suffocate and rot.
For healthy containers, a specialized potting mix, often called a soilless mix, is required to maintain a porous structure. These mixes are engineered to balance water retention with excellent aeration, typically containing lightweight and coarse ingredients. Organic materials like sphagnum peat moss or coconut coir (coir) act as sponges, holding moisture and nutrients.
Inorganic amendments like perlite or vermiculite are incorporated to ensure proper drainage. These materials create permanent, non-compacting air spaces within the mix, allowing gases to exchange freely around the roots. A lightweight potting mix provides the foundation for a thriving container garden.
Managing Drainage and Weight in Large Containers
Ensuring excess water can escape the container is a requirement for root health, meaning every planter must have unobstructed drainage holes. Placing a layer of rocks, broken pottery shards, or gravel at the bottom of the pot to improve drainage is a common but incorrect practice. This is counterproductive because it creates a phenomenon known as the “perched water table.”
The perched water table is a saturated zone that forms just above the layer of coarse material where the finer potting mix meets the gravel. Water will not drain into the coarser layer until the finer mix above it is completely saturated, raising the standing water level closer to the plant’s roots. This saturated zone deprives the roots of oxygen, promoting decay. To prevent this, the potting mix should be placed directly over the drainage holes, perhaps with a piece of mesh to prevent the mix from washing out.
For very large planters, the volume of potting mix can create a heavy container that is difficult to move. Instead of filling the entire volume with potting mix, lightweight filler materials can be used in the bottom half of the pot. Clean, inverted plastic nursery pots, empty water bottles, or specialized foam packing peanuts can take up space without adding significant weight. This method reduces the amount of potting mix needed while ensuring the container remains manageable for repositioning.
Plant Selection for Visual Design
After preparing the container, plant selection is guided by aesthetic and environmental considerations. A popular framework for container design is the “Thriller, Filler, Spiller” technique, which uses three distinct plant types to create a balanced, three-dimensional arrangement. This formula ensures the finished planter has visual interest.
The “Thriller” plant is the focal point, providing a strong vertical element and height in the center or back of the container. This plant should be the tallest component and is selected first to anchor the arrangement. Examples include ornamental grasses, upright fuchsias, or tall canna lilies, which draw the eye upward.
The “Filler” plants are mounding, rounded varieties that surround the thriller, adding mass, texture, and color to the middle layer. These plants occupy the space between the thriller and the container edge, giving the composition a full, lush appearance. Petunias, coleus, or begonias are commonly used as fillers.
Finally, the “Spiller” plants are those with a trailing habit, positioned near the edge of the container to cascade downward over the rim. Spillers soften the rigid lines of the pot and create a sense of movement. Sweet potato vine, creeping jenny, or calibrachoa are excellent choices for spilling over the sides.
Beyond the design framework, all plants selected for a single container must share similar cultural requirements. All components must thrive under the same sun exposure and tolerate the same watering schedule. Selecting plants that mature to an appropriate size is also important, as overcrowding can lead to poor air circulation and disease.
Ongoing Container Care and Feeding
Once planted, containers require more intensive maintenance than in-ground gardens, primarily concerning nutrition and moisture management. Because the potting mix is repeatedly watered, nutrients are continually leached out of the drainage holes. This loss necessitates a consistent schedule of fertilization, which should begin a few weeks after planting.
Gardeners can choose between two main feeding methods. The first is using a slow-release granular fertilizer mixed into the potting medium at planting. The second is applying a water-soluble liquid fertilizer every one to two weeks. Slow-release products release nutrients gradually over the season. Liquid feeding provides immediate nutrition but requires more frequent application.
Container plants dry out much faster than those in the ground, especially in smaller pots or during hot weather. Check the soil moisture by inserting a finger a couple of inches deep. Water should be applied thoroughly until it drains freely from the bottom. This deep saturation ensures the entire root ball is moistened and helps prevent the buildup of mineral salts.