Planting in an oversized container, generally considered anything 15 gallons or larger, poses unique challenges compared to standard pots. The sheer volume of material required makes excessive weight, drainage capacity, and the cost of soil significant factors. Successful growth depends on specific preparation techniques that maximize aeration and manage moisture within the large environment. These methods ensure the root system develops properly and the plant can thrive long-term.
Preparing the Container and Managing Weight
The initial placement of a large container is a permanent decision, as a fully planted pot can easily weigh hundreds of pounds and become impossible to move. Before adding any material, determine the final location and ensure the container has adequate drainage holes. Large pots require proportional drainage; a few small holes may not be enough to allow water to exit quickly, and additional holes may need to be drilled to prevent waterlogging.
To reduce the cost of potting mix and the overall weight, lightweight fillers are often used to occupy the bottom third of the container volume. Materials like empty plastic bottles, non-dissolving packing peanuts, or upside-down smaller plastic nursery pots work well. This strategy provides volume while maintaining a manageable weight. However, for containers in high-wind areas, heavy fillers like bricks or gravel can be placed at the bottom to serve as ballast, anchoring the pot.
Selecting and Layering the Planting Medium
The growing medium used in large containers must be light and porous, which is why standard garden soil is unsuitable. Garden soil is too dense; it compacts easily and retains too much water, which can suffocate roots. Instead, use a high-quality, specialized potting mix formulated with ingredients like peat moss, coir, or composted bark that promote aeration.
Mixing in materials such as perlite or pumice can further enhance the medium’s structure, creating air pockets that allow oxygen to reach the root zone. When using lightweight fillers, place a breathable barrier, like landscape fabric, directly over the filler material. This barrier prevents the potting mix from migrating down and compacting the filler, which would compromise drainage. Avoid the old practice of adding a layer of rocks or broken pottery to the base of a pot, as this raises the perched water table and hinders drainage.
The Final Planting and Settling Process
Once the container is prepped, remove the specimen from its nursery pot and examine the root ball. If the roots are tightly coiled or circling, lightly score or loosen them to encourage spreading into the new potting mix. Position the plant so the top of the root ball sits a few inches below the rim of the pot, creating a basin for watering.
Backfill the sides of the root ball with the prepared potting mix, gently firming the medium around the roots to eliminate large air pockets. Do not pack the soil down tightly, as this leads to compaction and poor water penetration. The final step is a thorough initial watering until water flows freely from the drainage holes. This settling process ensures the new medium is fully hydrated and eliminates remaining air pockets.
Watering and Maintenance Considerations
Due to the large soil volume, a big container takes longer to dry out than a small pot, requiring less frequent but deeper watering. When watering, apply enough to soak the entire root zone, encouraging deep root growth. Although large volumes hold moisture well, the sheer mass of the plant will demand a consistent supply of water, especially during peak growing seasons.
Since watering gradually leaches nutrients out of the medium, a consistent feeding regimen is necessary. Incorporate a slow-release granular fertilizer into the potting mix at planting to provide a base feed. This should be supplemented throughout the growing season with a diluted liquid fertilizer application. Finally, a layer of mulch, such as wood chips or shredded bark, on the soil surface will help retain moisture and stabilize the soil temperature.