Coco liners are natural inserts, typically made from the fibrous husk of coconuts, used to hold soil in wire-framed planters and hanging baskets. These porous mats provide a rustic aesthetic and serve as the primary barrier between the potting mix and the open-air frame. The question of whether to line these natural containers with plastic arises from the conflict between the coir’s inherent properties and the gardener’s need to manage moisture. Adding a synthetic layer fundamentally alters the environment the coir is designed to create. Understanding how this modification influences plant health and mitigating potential risks is necessary before introducing plastic.
The Primary Role of Coco Liners
The inherent design of coco liners promotes a healthy root environment through balanced water management. The loose, fibrous structure of the coconut coir provides excellent aeration, allowing oxygen to reach the roots efficiently. This breathability prevents the anaerobic conditions that lead to common plant diseases. The porous nature of the material also allows excess water to drain freely, defending against waterlogging.
Coco liners possess a moderate ability to retain moisture within the coir fibers despite their free-draining properties. This dual function of drainage and moisture retention makes them a popular choice for container gardening. The material keeps the root zone consistently moist but not saturated, establishing a stable environment for plant growth. Additionally, the coir has a near-neutral pH, which supports a wide variety of plants without altering the soil chemistry.
Why Gardeners Consider Adding Plastic Lining
The main reason gardeners consider adding a plastic lining is to combat the rapid drying rate of hanging baskets, especially in high-heat or windy locations. Water loss occurs through evaporation from the soil surface and lateral seepage through the porous coir walls. This quick drying means some baskets require watering multiple times a day during peak summer heat.
The plastic layer acts as a containment barrier, significantly slowing down both evaporation and lateral seepage. By keeping moisture trapped inside the liner, the gardener reduces the frequency of watering needed to maintain adequate soil saturation. This intervention is often viewed as a practical time-saver for plants sensitive to drying out. The plastic converts the highly permeable coco liner into a more water-retentive container.
The Importance of Drainage Holes
Introducing an impermeable plastic layer eliminates the natural, all-around drainage provided by the coir, creating a significant risk. If the plastic is not perforated, the container essentially becomes a bucket, and the potting mix will remain saturated after watering or rain. This condition leads to root suffocation, as the water displaces air pockets in the soil, causing the roots to rot from lack of oxygen.
Without proper drainage, the plastic liner also traps mineral salts left behind as water evaporates, leading to a toxic buildup that inhibits plant health. If plastic is used, it must be properly perforated to ensure vertical drainage is restored. For a standard 12-inch basket, punching three to four holes (1/4 to 1/2 inch in diameter) in the bottom of the plastic liner is sufficient. These perforations allow gravity to pull surplus water out of the root zone, preventing a stagnant, waterlogged environment.
Practical Alternatives and Final Verdict
Gardeners seeking to improve moisture retention without introducing plastic have several alternatives that maintain the coir’s natural breathability.
Thicker Liners
One approach is to use a thicker coir liner, as the increased mass of fiber naturally holds more water and slows evaporation.
Soil Amendments
Mixing water-retaining polymer crystals or vermiculite into the potting soil can boost the mix’s capacity to hold moisture. These amendments absorb water and release it slowly, benefiting the roots without obstructing drainage.
Natural Barriers
Other natural materials, such as burlap or old wool mats, can be used as a less-obstructive inner layer than plastic. They are more breathable while still slowing water movement.
The use of plastic lining is only advisable if the gardener is meticulous about adding adequate drainage holes to prevent root rot. For most home gardeners, utilizing a water-retentive potting mix and selecting a non-plastic alternative is a simpler, safer approach to moisture management.