Large planters, typically defined as containers exceeding 20 gallons or 18 inches in diameter, offer a significant visual impact to any space. These sizable vessels allow for the creation of miniature gardens that can house larger plants or complex mixed arrangements. Successfully planting and maintaining them requires specific techniques, as the increased volume and weight mean the process differs substantially from managing smaller potted plants.
Setting Up the Container and Location
Before introducing any material, select the container’s permanent placement. Once filled with soil and water, a large planter can weigh hundreds of pounds, making relocation nearly impossible. Consider the sun exposure, wind patterns, and aesthetic context of the surrounding area before committing to a spot.
The container requires careful inspection of the drainage system, as adequate drainage is necessary to prevent waterlogging and root rot. Ensure multiple drainage holes are present at the bottom of the vessel. To facilitate drainage, the container should be slightly elevated using risers or specialized pot feet, ensuring the holes are not blocked by the surface underneath.
Strategic Filling and Soil Selection
Filling a large container entirely with commercial potting mix is challenging due to cost and weight. A technique specific to large-scale planting involves using lightweight, non-decomposing materials to occupy the bottom third of the vessel. This strategic displacement reduces the volume of costly soil needed and significantly lowers the container’s total mass.
Suitable filler materials include inverted empty plastic nursery pots, clean plastic bottles, or specialized drainage packing peanuts. It is important that this filler material does not decompose over time, as settling would create an air pocket and compromise the root structure. Avoid organic materials like bark chips or gravel because they break down, compact the soil, and impede drainage.
Above the filler layer, only high-quality, sterile commercial potting mix should be used for the root zone. Garden soil is inappropriate for container gardening because its fine texture lacks the necessary porosity and aeration, causing it to compact densely when watered. Potting mixes are engineered with components like peat moss, perlite, and vermiculite to maintain an ideal balance of moisture retention and air pockets for healthy root respiration.
Arranging and Planting the Vegetation
Arranging the plants focuses on maximizing visual appeal and growth potential. A common design method for mixed arrangements uses three types of plants:
- A tall, focal “thriller” plant placed centrally or toward the back.
- Mounding “filler” plants that provide mass and color in the middle ground.
- Trailing “spiller” plants positioned near the edges to cascade over the rim.
Before placing plants, gently remove them from their nursery containers and examine the root ball. If the roots are tightly coiled or circling, they should be gently teased apart or sliced vertically to encourage outward growth into the new soil.
Install each plant so the top of its root ball, known as the crown, sits level with the potting mix surface. Planting too deep can lead to stem rot, while planting too shallow exposes the roots. After placement, gently firm the potting mix around the base of each transplant to eliminate air pockets.
The final step is a thorough, heavy initial watering until water pours freely from the drainage holes. This action settles the soil firmly around the roots and ensures the entire soil column is uniformly moistened, initiating healthy establishment.
Long-Term Care for Large Planters
The large volume of soil retains moisture longer than small pots, but when a large planter finally begins to dry out, the entire column of soil can become desiccated rapidly. Monitoring moisture levels by inserting a finger several inches into the soil is a more reliable method than simply observing the surface.
The larger plants housed in these vessels quickly deplete nutrient reserves. Unlike in-ground plantings, container plants rely entirely on supplied nutrients, making a regular fertilization program necessary to sustain vigorous growth throughout the season.
This feeding can be achieved through the incorporation of a slow-release granular fertilizer mixed into the top layer of soil at the beginning of the season. Supplementing this with a diluted liquid feed applied every two to four weeks ensures a continuous supply of macronutrients like nitrogen, phosphorus, and potassium, which is important for lush foliage growth.
Seasonal care requires attention, particularly in regions with freezing temperatures. Tender perennials or shrubs may need protection, often involving moving the entire container to a sheltered, unheated space like a garage or shed before the first hard frost. Even hardy plants should be monitored, as roots in an above-ground container are more exposed to cold damage than those insulated by the ground.